Stopping an invasion of Raccoons, Skunks, Opossums, Rodents, Feral Cats, and a Fox, at a home in Northwest Austin… 1

This article by Jerry Cates, first published on 25 January 2015, was last revised on 25 September 2016. © Bugsinthenews Vol. 16:01(01):



Fig. 1. Void under porch, where — via a hole dug in the ground under the concrete skirt (fig. 2) — skunks, raccoons, opossums, feral cats, foxes, and rodents were getting under the house.

Summary: The following chronicles the invasion of a northwest Austin home’s crawl space by raccoons, opossums, skunks, feral cats, a fox, and one or more rodents. It asks and answers why a well-known, reputable pest control company had previously failed to bring the invasion to a halt. It then describes how the author, using advanced, humane wildlife management techniques, removed and permanently excluded these animals from the home’s crawl space. Finally, it explores and solves one final question: Why did these animals invade this home’s seemingly secure crawl space in the first place? If you appreciate a good puzzle, explore this one with the author as he examines the twists and turns of wild animal behavior, and offers a glimpse into the ways that wild animals interact. The insight he sheds on steps homeowners may take to prevent animal invasions at their homes is invaluable.


For help with your pests — including wildlife invasions in attics, walls, or crawl spaces, and such pests as bedbugs, mites, springtails, invasive ants, scorpions, snakes, etc. — call EntomoBiotics Inc. at our Pest Hot Line: (512) 331-1111We’re available, 24/7/365, to answer questions about, or to provide help with all your pest management issues. 


EntomoBiotics Inc. has been engaged in the field of pest management and wildlife control, all over Texas, since 1980. It is safe to say that, in the past 34 years, we’ve had to deal with nearly every wild animal Texas has to offer.

In early March 2013, a call was received from a homeowner, in northwest Austin, whose home was being invaded by wild animals. Earlier, the homeowner had called in another pest control company to deal with the invasion. Yet, despite strenuous control efforts by their supervisory and technical personnel, the daily incursions of wild animals, which that company was being paid to resolve, had continued unabated.

The animals were nesting and loitering in the crawl space beneath the home’s flooring. From time to time over the past year or so, the homeowners had noticed chirps, squeals, and other animal noises coming from under the hardwood floor. Later, the pungent odor of skunk musk permeated the living space after what sounded like a growling, spitting fight had taken place under their feet. At that point they’d had enough and sought professional help.

This home, in an older, established northwest Austin neighborhood near a heavily forested area, was built on a pier-and-beam foundation, with an extensive crawl space. The  foundation surface was intact all along its perimeter, making it impervious to wild animals. Its footing had been sunken into the soil some 6-10 inches to make it even more secure. Still, at some point in the past several years an enterprising wild animal of moderate size had excavated a hole approximately six inches in diameter in a corner of the home’s perimeter, under an overhanging porch. The hole extended down, under the skirting, then turned upward and emerged on the other side, inside the home’s spacious crawl space. Several species of wild animals were now using that hole to enter, exit, and nest within the void the crawl space afforded.

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Fig. 2. A closeup of the hole, in the soil next to the foundation, where wild animals of moderate size were entering and exiting the crawl space of this home. No other holes that would accommodate animals larger than a burrowing rat could be found around the perimeter of the home. A much smaller hole (Fig. 12) was found 8 ft. away from this one, also next to the foundation, but, again, it was the only small hole that was found around the perimeter of the home.

Days before calling in the first pest control company, and several weeks before consulting with EntomoBiotics Inc., the animal fight that prompted these homeowners to seek professional assistance took place. Now, as one of the homeowners described over the phone how their first pest control company had attempted to quell the animal invasion, I was reminded of a multitude of other wildlife control failures I’ve been called to in the past.

A common, seemingly logical approach that doesn’t work…

That first pest control company’s supervisors had instructed the company’s technicians to bring a number of Havahart® wild animal traps to the home. These they’d baited with food before placing them under the house, within the crawl space. No steps were taken to seal or otherwise modify the ingress/egress port being used by the wild animals. Within days each of the traps had caught at least one wild animal of several species, though we were not provided a record of how many of each species were caught.

The pest control technicians returned every few days to remove the trapped animals, transport them some distance away, and release them into the wild. How far the animals were transported was not specified, but the homeowners were assured it was far enough to prevent the animals from returning to this home.

Though that company did not promise an immediate solution, their representative explained that the process was self-limiting and would not take “all that long” to complete. “The important thing to realize,” the representative said, was that “only a finite number of animals were nesting in the crawl space, and every animal that was trapped, relocated, and released would reduce that number incrementally.” Thus, “Before long, the very last animal would be caught and transported away, out of their lives for good…


Fig. 3. One way door (OWD) installed at this site, over the hole used by wild animals to gain access to the crawl space of this home.

Intuitively, the idea of trapping and relocating all the wild animals invading their crawl space made excellent sense. Banking on that, the homeowners had watched and waited, trying all the while to be patient. But the number of trapped animals that were picked up on subsequent service visits seemed about the same as at the beginning. As days ticked by, and that pattern continued, their patience dimmed. Still, they were assured that they had no choice but to allow the project to run its course.

Then, it happened… again. A few days before they called EntomoBiotics Inc., another growling, spitting fight took place under the house. As before, the living space of the home was engulfed in the foul odor of skunk musk. Soon thereafter, this time following an Internet search that found an article I’d written on wild animal exclusions, they’d decided it was time to explore a new approach.

A counterintuitive approach that works every time…

I just read on the Internet…” the homeowner began after I answered the phone, “… about how you solved an invasion of raccoons at a commercial structure in Denton. You were called in after another pest control company spent months trying to resolve that problem. If we read that article right, you were able to fix things in a matter of days, permanently. We have a similar predicament here in northwest Austin. Our pest control company is doing exactly what that company in Denton, that you replaced up there, tried to do, and it isn’t working for us, either. Do you think you can fix things down here the same way you fixed the raccoon invasion in Denton?”

I told this homeowner it was no surprise that trapping, relocating, and releasing the offending animals wasn’t working. That method almost never works, even when the trapped animals are euthanized. It isn’t because the relocated animals return. They probably are being taken far enough away that they can’t, or won’t go to all the effort necessary to get back. But, besides the fact that the now-relocated animals will become somebody else’s problem, the endemic wild animals that populate the area around this home are so numerous that, for every animal that is trapped and relocated, a new one quickly comes in and takes its place. Most Texas homeowners — and for that matter, most Texas pest control companies — have no idea how many wild animals pass through the typical residential yard every night. In most places, even in the hearts of large Texas cities, that number, if known, would be a source of utter amazement.

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Fig. 4. The ingress/egress hole, inside the OWD, that mates to the wild animal hole in the soil next to the home’s foundation. This hole allows wild animals, inside the crawl space, to leave the crawl space and enter the OWD. Once inside the OWD they inspect the OWD interior, and soon discover the easily manipulated door that lets them exit from the OWD to the yard. At that point, however, they are unable to reenter the OWD to get back into the crawl space. Note the sprinkler head in the left half of the image. The OWD had to be built around this sprinkler head in order to get the OWD installed quickly; the sprinkler head was later removed and relocated away from the OWD.

As for the last question, yes, I expected that the final solution to their situation would follow a path similar to the one that had been successful in Denton. But first it would be necessary to inspect the premises and determine the exact nature and scope of the invasion.

The setting…

We made arrangements for me to come out right away. What I found was a neat and tidy home, and a yard teeming with botanicals that included lush ground covers, shrubs, vines, and trees.

A thorough inspection of the home’s exterior found one large ingress/egress hole that was being used by a variety of moderately sized wild animals, and a smaller hole, some 8 feet from the larger one, that appeared to be used by a burrowing rodent. No other routes of ingress to the home’s crawl space were noted, but these two, and particularly the larger one, were sufficient to permit regular traffic of a wide variety of wild animals.

At the completion of the inspection, I told the homeowners that solving the wild animal invasion at their home would be relatively straight-forward. I would make sure all the wild animals were out from under their house within a few days. Furthermore — with some help from them — I’d make sure they were kept out permanently. And the fee I’d charge wouldn’t break their budget.


Fig. 5. The author, inspecting and photographing the interior of the OWD, two days after it was installed, at which time it was believed that all the wild animals had successfully exited the crawl space of the home. The OWD remained “unlocked” (its one-way-door functionality was kept fully operational) for several more days to ensure no stragglers remained behind, inside the crawl space. At that point it was “locked” (its one-way-door functionality was removed) to prevent further use of the OWD. The apparatus had to remain in place until, through the use of a wildlife camera installed under the porch, it could be determined that endemic wildlife was no longer making serious attempts to reenter the home’s crawl space.

Mechanical exclusion, done right, always works.

There exists one quick, humane, and effective way to deal with wild animals that are invading and nesting in the voids of a home. Regardless of whether animals are invading the walls, the attic, or the home’s crawl space, the correct installation of one or more properly designed, specialized exclusionary devices, is the single best way to get them out.

To keep them out permanently, however, the conditions that led to the invasion in the first place have to be identified and corrected. If that isn’t done, another invasion will almost certainly take place. But, once those conditions are addressed and permanently nullified, wild animals should never invade this home again.

Trap, relocate, and release methods almost never bring wild animal invasions to a halt.

It bears repeating that trapping, relocating, and releasing the offending animals almost never produces a satisfactory outcome. The process is also fraught with legal and ethical issues, one of which was mildly alluded to earlier.

Suffice it to say that, in order to bring wild animal invasions to a quick and permanent end, mechanical exclusion is the preferred approach, for reasons discussed briefly below.

The dynamics of wild animal dispersals in rural, suburban, and urban settings…

Wild animals are spaced, within our landscapes, in accord with  localized, overlapping spatial territories. Those territories are established and defended by dominant adults of each of the wild animal species represented in that area. The dominant adults emerge, as needed, from a pool comprised of an almost infinite number of subordinates. Reproduction rates, mediated by population densities and food supplies, are particularly high in urban and suburban settings due to the abundance of nourishment. The rates are so high, in fact, that experienced wildlife specialists accept as a given that most species of wild animals within such settings will replenish their missing members — i.e., those that either die or that have been relocated — in short order, with little or no perceptible delay.

Most of the wild animals nesting within a particular defended territory utilize a string of scattered, temporary nests that — except for females suckling young — are visited in a relatively random pattern. Foraging routes change from day to day, but as the night sky brightens in the east all nocturnal foragers begin to seek out and take shelter at nearby nesting spots, choosing those that are most convenient at the moment. There they settle down, out of sight, to rest and sleep while awaiting the coming nightfall. One wildlife biologist, in an explanation of raccoon nesting selection, described the process in these words:

Though they may use some spots more frequently than others, raccoons repeatedly change their sleeping sites, even on a daily basis. In Kansas (for example), their average occupancy period for resting dens was only 1.5 days. (Leveloff. 2002. Raccoons, A Natural History. Smithsonian Institution Press, pg. 96.)

Many if not most other species of carnivorous wild animals also utilize scattered, temporary nests. Most of the time, such animals don’t build nests from scratch, but take advantage of opportunistic nesting spots that are formed naturally or that were created by others. Thus they have little or no direct investment in the nests they occupy. This is especially true for nests within the voids of a crawl space or attic often found at typical residential or commercial structures. It is rare for the nests in such places to be established at fixed, permanent locations. The latrines used by some species of nesting animals tend to be localized, giving the uninitiated the impression their nests are nearby and just as localized, but such is rarely the case. The abundance of suitable, cryptic nesting spots present in such voids makes it practically impossible to find them all in a single inspection.

This nesting dynamic explains why one can trap, relocate, and release scores of wild animals that are nesting at any given site without making a noticeable dent in the total number of animals that nest there. As long as newly arriving animals have unrestricted access to the site’s nesting voids, a regular invasion of wild animals there will continue without respite.

Then, why not just seal up the hole and be done with it?

That, in fact, is what most do-it-yourself homeowners do. The consequences, however, are always bad. Sometimes they are devastating.


Fig. 6. A cat, presumably feral, inspects the OWD apparatus on 26 March, 14 days after the apparatus was installed. This was the first wild animal imaged, after all animals had been excluded from the crawl space, by the wildlife camera the author installed under the porch to monitor wildlife activity. A succession of wild animals followed over the next two months, including several cats. Feral cats commonly use holes dug by other wild animals to access, forage within, and nest in voids in the walls, attics, and crawl spaces of homes.

Many wild animals are either crepuscular or nocturnal, though some, like the gray fox, may forage throughout the day. The general foraging pattern, as described earlier, is random. Some wild animals remain in their nests for one or two days without leaving. For that reason, experienced wildlife specialists know better than to assume that all the nests in a home’s voids are totally vacant at any time of the day or night.

Sealing up an ingress/egress hole to a home’s void is, by itself, a tricky business. How should the seal be constructed? How can it be done so that it does not encourage wild animals to defeat its purpose? Most such seals are made to return the sealed surface to its original appearance, and often the result is a surface and substrate that is easily penetrated, both from inside and outside the void.

Merely filling ingress/egress holes in the soil with rock, sand, or soil encourages excluded and imprisoned animals to re-excavate the original hole. Savvy specialists know from hard-earned experience how ineffective such methods are. Reentry efforts by excluded animals become all the more determined if they hear cries made by an animal imprisoned in the void.

Even if the seal is competent enough to prevent animals from defeating it, oftentimes at least one wild animal will become imprisoned inside the void. The imprisoned animal, in a panic, goes to work trying to fashion a new exit. In the process it damages the home’s structure. Often the animal succeeds in making a new exit hole in a weak point in the foundation, through which the old invasion resumes.

Ok… so why not just seal up the hole, then trap, relocate, and release the animals imprisoned in the void?

Intuitively this seems to make sense, so one might reason that, if it is carried out, any animals imprisoned in the sealed up void will easily be caught in baited Havahart® traps. They can then be relocated and released. The original pest control company called in to deal with this animal invasion did not make the mistake of sealing the ingress/egress hole, and that was a good thing, even if the remainder of their efforts were off the mark.

Most inexperienced pest managers often choose this approach — sealing the ingress/egress hole, then trapping the animals imprisoned inside the void in baited Havahart® traps — as a “quick and dirty” way to solve the problem. Unfortunately, though, a number of unacceptable risks accompany that process. As mentioned earlier, imprisoning a wild animal changes the way it behaves, often markedly so. Most imprisoned animals panic when cornered, and imprisonment is akin to being cornered.  It is common for an imprisoned animal to lose its appetite, and refuse to enter baited traps. Such animals focus instead on mounting an aggressive attempt to find or make a way out. The emotional stress on the imprisoned animal is severe.

Obstinate animals imprisoned in a home’s void often starve to death without entering a trap to access the food contains. Since entering a void occupied by an imprisoned, uncaged animal risks an attack by the animal, human entry into the void before the imprisoned animals therein have died is unwise. Even if one or more animals enter the baited Havahart® traps, it is impossible to be certain that another animal isn’t still on the loose. The safest approach, then, for the human, is the most cruel way to deal with the animal, because maximizing human safety requires all the imprisoned animals to succumb to starvation before the void is entered.

A long list of additional negative issues, all associated with the “seal, trap, relocate, and release method,” could be appended to this discussion. The issues already mentioned, though, offer sufficient proof to the wise that it just isn’t a good way to go…


Fig. 7. The properly reinstalled OWD apparatus, after the lawn sprinkler head was removed by a handyman service company technician. The technician that removed the lawn sprinkler head was not wildlife-savvy, and initially reinstalled the OWD apparatus in such a way (by leaving the OWD projecting aboveground, with a wide gap between the OWD and the foundation wall) that any wild animal that was determined to defeat its purpose would likely have succeeded in doing so. A raccoon visited the site that evening. Though conducting a thorough inspection of the OWD it did not notice how easily it could have pushed the OWD away from the original ingress/egress port to reenter the crawlspace. The author returned the next day and returned the OWD apparatus to its initial, tamper-resistant state.

What to do?

Then what should be done? If trapping and relocating doesn’t work, and sealing up the ingress/egress hole often leads to new damages without solving the problem, what’s left to do?

Installing an OWD — the best way to effect mechanical exclusion…

Fortunately, there is a simple answer to this question. One needs only to craft and install a specially designed, properly constructed one-way-door (OWD) apparatus that covers the hole where the animals are entering and exiting the home’s void. The OWD is left in place until all the wild animals have safely and permanently removed themselves from the nesting void. It is then sealed shut, and kept in place until those wild animals cease to include the home’s voids in their inventory of desirable nesting spots.

An OWD that is properly constructed will allow all ambulatory animals inside the crawlspace to get out, yet won’t let any of them come back through. Still, designing and building an OWD apparatus that works — like almost everything else associated with wildlife management — is not a trivial matter.

The cryptic art of OWD design and construction…

Building OWD devices to exclude wild animals is a cryptic, almost mystic art. No worthwhile “how-to” manuals for OWD design exist, although generalized versions of one-way-door excluders can be purchased through some wildlife control suppliers. Where they can be used, such generalized excluders are convenient, but in most instances neither the architecture of the ingress/egress port being used by the animals, nor that of the structure in which the port exists, is amenable to their use. Thus I, and my colleagues who toil within this arcane field, are almost always forced to make specialized OWD devices tailored to the hole and the setting with which we are working at the moment.


Fig. 8. A striped skunk (Mephitis mephitis) visits the OWD on 29 March at 3:37 AM. This animal remained under the porch for several minutes, inspecting the OWD and the rodent bait station before leaving.

To permanently solve an existing wild animal invasion the OWD must perform to perfection, not only against the wild animals one is focusing on at the time, but against all of the wild animals perusing the general area. This is true because, if the OWD fails to work with any of the wild animals there, the ones that do get through usually manage to introduce defects that enable others, including those being targeted, to defeat the OWD as well.

So, like Edison in his classical search for a workable light bulb, at the beginning I had no choice but to keep trying new OWD designs, and tweaking imperfect ones until, with luck, intuition, and a string of bad experiences, I happened upon a near-perfect design that worked everywhere, and against every wild animal that I knew I’d find where the OWD was to be deployed.

Expertise must be constantly re-tested and reaffirmed…

My knowledge of OWD design is tested anew with each wild animal the devices are pitted against. Every site is different, so the lessons learned with other sites and other animals almost never mate cleanly with the next site and the animals that are encountered there.


Fig. 9. A raccoon (Procyon lotor) visited the space under the porch, 14 minutes after midnight on 30 March 2013. The raccoon inspected the OWD carefully, then loitered here much like the skunk of the previous morning, and left.

Most of the time, as in the case at this home, the OWD must be specially constructed, from scratch, tailored exactly to the setting.

The secrets of OWD design and construction…

Except for a few notes that follow on the subject of wild animal behavior, little can be provided here — in mere words — regarding the technical details surrounding OWD construction. It would be fruitless, in fact, to try to write a brief, easy-to-read piece about such a methodology.

Why? Because the secrets to the design of competent OWDs for wildlife control are not amenable to facile descriptions. The best way to discover those secrets is to learn them from the animals, by developing, and nurturing, a deep understanding of the ways in which they go about their daily lives.

Learning from the animals themselves…

As a curious adolescent in the early 1950’s, I began to learn how to let wild animals teach me their secrets. The logical foundation for that didactic was not a product of my native intellect. In fact, it arrived unwanted, and had to be forcibly imprinted upon my consciousness. I doubt it would ever have commenced for me, had I not first been severely rebuked by a grizzled old hermit. My hoary mentor, whose name was Bob Bolan, lived in a shack on a tract of forested land my father owned in the Missouri Ozarks.


Fig. 10. An opossum (Didelphis virginiana) passes through the area on 6 April, apparently at a rapid pace. It may have been spooked by something, as other opossums that visited here took their time inspecting and just nosing about.

Of all the people I knew, Mr. Bolan seemed to have the best grip on the ways wild animals think and behave. Realizing that, I’d hoped to get him to share his knowledge with me. So I asked, but at first he ignored my question. Then I begged, and he finally answered, but his answer was not what I wanted to hear.

“Lad,” he gently scolded, his harsh words laced with tender compassion for the youthful source of his exasperation, “I cannot possibly teach you what is only learned by listening to, watching, and communing with, the wild animals themselves.” 

His disappointing words dashed my childish hopes. At the time it seemed impossible for me to learn what I wanted to know from the animals directly. Much later, though, I realized that Bob Bolan was right.

… the mysteries of nature.

Chroniclers of nature, since time immemorial, have sought to become privy to the wisdom Bob Bolan shared with me. In every case their successes have only come after they’d paid the heavy price of long, careful observation, followed by much study and reflection. James Fenimore Cooper, in his 1826 book The Last of the Mohicans, exclaimed similar if not identical truths that he’d learned as a child on his father’s land, grounds the Iroquois of the Six Nations had long occupied. Longfellow conveyed that same sense in scattered lines within his epic 1855 poem, The Song of Hiawatha, and nearly 50 years later, Jack London — in his 1903 book The Call of the Wild — did much the same. While we rightfully celebrate their teachings, we must also admit that they were all latecomers to the art. It is no secret today, nor — as witnessed by these and a host of other examples — has it ever been in history, that the ways of the wild animals are not easily reckoned.


Fig. 11. A gray fox (Urocyon cinereoargenteus) visite the area under the porch on 8 April. Gray foxes are easily distinguished from red foxes, which are also common in this part of Texas, by the darkened distal tip of the gray fox’s tail. They den in underground burrows, hollow logs, and in voids of homes. Though omnivorous, they are particularly fond of small mammals such as cotton rats, pocket gophers, and pocket mice. It is likely this fox was a frequent visitor to this home’s crawlspace to prey on its wild inhabitants. It may have denned there as well.

The arduous work of uncovering the legitimate ethos, pathos, and logos behind nature’s mysteries — truths that Cooper, Longfellow, London and a multitude of other writers only dimly capture in words — was what my hermit friend, Bob Bolan, sought to point me toward. Distilled to its essence, it proclaims that there are no shortcuts to that peculiar species of wisdom.

I’ve since tried to accept and practice that momentous lesson. It is only as a result of this resolve that I have become successful at wildlife control. Yet, though I’ve conquered my personal naiveté, passing what I’ve learned on to others is always a challenge.

Back to the invasion…

The proven method I proposed to this homeowner is, as mentioned earlier, counterintuitive. It defies conventional wisdom. Unconventional methods, of course, not only elicit a degree of skepticism, but invite lots of questions. I do my best to answer those questions carefully and thoroughly. For example, when I try to explain the necessity and benefits of using an OWD apparatus to resolve wild animal invasions, the first question my listener usually asks is this:

“Why won’t the animal excluded by the one-way-door dig another hole? Or, like an animal imprisoned inside the crawl space, why won’t the excluded animal make a new way back in, perhaps at another spot along the old perimeter?”

The answer to that question can’t be supplied in one or two sentences. As that grizzled old hermit explained, in his rebuke to me over 60 years ago, such answers come only by delving into the vagaries of the wild animal’s mind, and that takes some explaining.

Here I will try to share a small portion of what I know, in hopes of providing at least tentative answers to those questions. To do that, we must first explore the subtle distinctions between excluded animals and imprisoned ones. Moreover, in the case of excluded animals, we must also distinguish how excluded animals with empty nests must be handled differently from those whose nests contain non-ambulatory young. The behavior exhibited by members of these two distinct groups is markedly different.

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Fig. 12. A rat burrow, next to the foundation about 8 feet from the larger animal burrow that had already been interdicted with an OWD apparatus. On finding this diminutive burrow on 12 March, the author stuffed it with smooth river rocks to determine if it was presently in use. The next day the rocks had been pushed out of the hole, confirming it was an active burrow. The burrow was then excavated, and found to extend laterally, beneath the concrete skirting of the home’s perimeter, and emerging on the other side, inside the crawl space. At that point the hole was filled with angular landscaping rocks that would be difficult for a rodent to excavate, then covered with soil, and capped with a heavy flat stone. Afterward no further activity was noted. The rat that had been using this burrow was believed to have exited the crawl space via the OWD apparatus 8 feet away.

The excluded animal…

Wild animals are not, in general, aggressively resourceful. This is not to say they are unintelligent or lazy, as they are neither.

As pointed out earlier, wild animals that are excluded from a void to which they have become habituated tend, at first, to make strenuous attempts to reenter that void. However, erecting an OWD has a strangely distracting effect. Installing a properly designed OWD over an invasion portal frustrates the excluded animals, and inhibits their efforts to circumvent the OWD by creating a new entry portal nearby.

As long as the excluded animals remain able to see the old entry portal, but are unable to pass through the OWD to get back to their nest, they focus on defeating the OWD directly. On failing to do so, they soon depart, returning hours or days later to try again. After several more unsuccessful attempts, they revert to shorter, unproductive visits that focus on merely determining whether or not the OWD is still in place. On finding that it is, the animal loiters in the area briefly before departing for an alternate nesting spot.

By virtue of a serendipitous event, the distracting effect of the OWD installed at this site was tested a few days after it was installed. It was necessary to install the OWD as quickly as possible, which gave no time to remove a lawn sprinkler head that was located near the hole that wild animals were using to access the home’s crawlspace. So, the OWD was initially placed over the sprinkler head.

A few days later a handyman, who had been called in by the homeowner, dropped by to relocate the sprinkler head. In the process, the OWD had to be pulled up by the handyman technician. After removing the sprinkler head the technician made a feeble attempt to return the OWD to the state in which he’d found it. The result was that any wild animal could easily have bypassed the OWD and re-entered the home’s crawlspace.

That night, as recorded by a wildlife camera I’d previously installed, a raccoon visited the site, and though the animal inspected the OWD, it made no attempt to circumvent it. Instead — as in previous inspections — the raccoon was distracted by the fact that the OWD was still in place, though loosely, over the original access hole. The next day I happened by, noticed the problem, and reinstalled the OWD in a proper state of functionality (Fig. 7). Later that day I downloaded the images from the wildlife camera, and reviewed the images of the handyman removing and replacing the OWD, as well as those that recorded how the raccoon, only hours after the handyman had gone, had inspected the OWD before departing.

From this, combined with evidence collected during other wild animal exclusion projects, it appears that wild animals tend not to be overly obsessed with past nesting spots. The reason why appears simple enough: they don’t have to search hard, within their defended territories, to find a wealth of acceptable places to rest and sleep. The moment one is lost to an OWD or some other impediment, another is — albeit with some reluctance — selected to take its place.

… and an important exception.

An exception occurs when non-ambulatory young are still in the old nest. Maternal instincts give female adults added incentives to find a way back. That incentive often translates into aggressive reentry efforts even when a properly designed OWD obstructs the old entry port. Experienced wildlife specialists take that into account by, whenever possible, scheduling wildlife exclusions when nests are empty.

If that cannot be done, the specialist must reenter the void, immediately after all wild animal adults have been excluded, to search for young that may not have been able to reach and exit through the OWD. If such are found, they must be dealt with humanely, in accord with local, state, and federal law.

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Fig. 13. Lush ground cover, in this photo mostly African violets, but elsewhere in this yard composed of a number of other forms of thick, short-height ground covers that provide excellent harborage for a teeming, though largely invisible, rodent population. Such harborage — if not interdicted — usually leads to at least eight predictable consequences. Those consequences are described in the narrative of this paper, below.

At this home, though, the probability of nest-bound, non-ambulatory young was unlikely…

The timing of this exclusion was such that the presence of non-ambulatory young in the nests under his home was unlikely.

As long as a good, competent OWD apparatus could be installed at the large ingress/egress hole, all the wild animals nesting or resting in this home’s crawl space should have been able to pass through it within the first two or three days after it was installed.

Since none of them would be able to return to that void, the invasion would immediately be brought to a halt, without risking the imprisonment of any wild animals inside the crawl space.

Imprisoned animals…

That last point is important. An imprisoned animal has no choice but to take every step available to find a way out of its prison. That quest is a matter of life or death and, given a choice, the wild animal prisoner goes to whatever lengths are available to gain its freedom and preserve its life. Often, as mentioned earlier, the effort is successful, and results in a fresh, two-way access port to the old nest.

When such efforts are unsuccessful, however, the imprisoned animal is subjected to considerable pain and suffering, and ultimately dies from lack of food and water. This is not a trivial matter, whether from a moral, ethical, or legal standpoint. Knowingly subjecting wild animals to such cruel and inhumane treatment constitutes, in most jurisdictions, a serious criminal offense.

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Fig. 14. Another expanse of lush ground cover in the back yard of this residence. The structure at right is a corner of the porch that overhangs the section of foundation where wild animals were entering the home’s crawl space.

Experienced, responsible wildlife specialists take positive, effective steps to treat the animals they deal with in a humane manner. They are fully aware of, and act in strict obedience to, all the laws pertaining to wildlife and animal husbandry within the jurisdictions wherein they are employed.

The management of wild animals must be carried out, not only in consonance with man’s laws, but with the laws of nature that are not codified. In the process, the conduct of the responsible wildlife specialist is such that it never violates either the spirit or the letter of either. When guided by that credo, the work the specialist performs is rewarded with successes that benefit the clients whom the specialist serves.

Skepticism, borne out of a seeming contradiction…

I told these homeowners that once the animals presently invading the crawl space at this home could be properly excluded, it would thereafter be possible to keep them out permanently. I could see in their eyes, though, that they were doubtful.

Wasn’t it true, I was asked, that at some point in the recent past wild animals had gone to great lengths to dig a hole under the skirt of our home’s foundation?

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Fig. 15. An expanse of thick vines along the righthand perimeter of this residential yard.

Yes, I replied, that most definitely happened.

Then, why doesn’t that contradict your assertion that these wild animals can be managed to the point that they won’t go to similar lengths in the future, digging another hole under our home’s foundation, and invading its  crawl space again?

This perceived but imaginary contradiction stemmed from a belief that these wild animals had dug the larger hole — the one that was to be covered by the OWD — for the express purpose of gaining entry to their home’s crawl space. That belief assumes that the animals knew, in advance, that a crawl space was there, and consciously sought to exploit it as a place in which to rest and nest.

Though wild animals are amazing creatures, no wild animal is capable of such judgements. In fact, humans aren’t much better. The skirting on this home’s foundation has the identical outward appearance of the foundation skirting on homes built on monolithic slabs, which do not have crawl spaces; it is not generally possible, even for a human, to distinguish between the two using external visual evidence alone.

This leads us to only one legitimate conclusion. The wild animals that initially dug the hole into this home’s crawl space were not motivated by knowledge that the hole they were digging led to a void in which they could nest. The original purpose of the hole the wild animals dug, then, must have had nothing to do with gaining entry to a crawl space. Something else had to motivate them to excavate that hole. It is crucial that we identify the actual cause, because, once it was identified it could be dealt with, hopefully in a way that prevents any future wild animal from attempting to excavate a portal into this home’s crawl space.

The nature of that cause — which we identified in the course of this project — is fully explained in what follows, below. But first, the results: how well, how quickly, and how painlessly did the OWD crafted for this home work after it was installed? And how much did this project cost the homeowners?

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Fig. 16. A thick expanse of English ivy along the front of the home. This ivy was immediately removed, the brickwork was taken up, and pavers were expertly installed, by the homeowners, in their stead.

Finally, bringing this wild animal invasion to a halt…

The OWD apparatus, assembled in the EntomoBiotics Inc. lab specifically for this site, was installed a few days after the homeowners called. Within the following two days all animal activity under the home ceased. The site was later monitored, night and day, using a wildlife camera equipped with infrared illumination. Because the wild animals could not detect the presence of the camera, they behaved normally, even as the camera noiselessly documented their comings and goings. Use of that camera continued for two months afterward. From the images the camera collected it was possible to confirm and document the successful resolution of the wild animal invasion. No invasive animal activity at this site has been noted since. The entire process was quick, effective, and essentially painless.

The fee charged for this work was reasonable by any standard. When the full amount that was to be charged was explained, up front, the homeowners were visibly relieved. That told me our proposal was probably for a lesser amount than they had already paid the pest control company that preceded us. I and they knew that previous work had accomplished nothing, had extended the animal invasion for weeks, and had enabled — on that company’s watch — a second wild animal fight that had once more filled this home’s living space with the foul odor of skunk musk. It was immensely satisfying to all that this frustrating and nightmarish experience would, in short order, be brought to a successful conclusion.

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Fig. 17. More thick English ivy vines along the front of the residence. This expanse of ground cover was also taken up by the homeowners and replaced with expertly placed pavers.

What about the permanence of the project? Did the homeowners’ initial satisfaction continue unchanged, or, as they had feared, did more wild animals find a new way into their home’s crawlspace, to start a new invasion? It is always important to get back in touch with our clients, months and years afterward, to make sure our work for them has continued to brighten their lives. If the results of that work are not as permanent as intended, then we study the aftermath, determine the reasons why a failure occurred, and make things right.

So, did it last?

The latest follow-up visit to the site, to again inspect for evidence of fresh efforts by wild animals to gain access to the home’s crawlspace, was conducted on 26 January 2015, nearly two years after the project described in this paper was completed. That inspection found no overt evidence of wild animals of any kind.

Furthermore, the homeowners have not seen or heard anything suggesting wild animals have ever invaded any part of their home over the intervening period. Many wild animals are, to be sure, still inspecting the yard and landscape on a nightly basis. That’s what wild animals do. But they aren’t nesting and living there.

But, now, how did those wild animals get into this home’s crawlspace in the first place?

That question poses an interesting riddle. It is also one that is worth the trouble to explore and solve. So we shall now delve into the genesis of the invasion that took place at this home, months or years before the homeowners even realized it was happening…

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Fig. 18. A closeup view of the English ivy covering large portions of the yard at this residence. Note the density of the ivy, and the decaying undergrowth. At this location the undergrowth was 6-8 inches thick, and provided excellent harborage for a variety of terrestrial and burrowing rodents.

Recall that, besides the moderately large hole next to the foundation, another, much smaller hole (see Fig. 12, above) was found, some eight feet away. It seemed evident at the time that this smaller hole had been dug by a burrowing rodent. Texas is home to over 68 species of rodents, and 24 of those are known to be found in Central Texas. Some of those rodents are expert burrowers. A number of them dig burrows into the soil that lead, at some depth below the surface, to a subterranean redoubt where they nest and raise their young.

Now take note of the fact that every nocturnally active wild animal that was later found, under the porch near the OWD-covered access hole into the home’s crawlspace, was an omnivore, which means that they will consume fresh and stored fruit and vegetable matter when such is in abundance, and animal flesh when the opportunity arises. Such animals are, preferentially, carnivores, and are especially fond of the young non-ambulatory nestlings of other animals. That makes them, by nature, a predator of rodents, as rodents are among the most prolific of our wild animals, in terms of their regular production of young. Some of them, including the fox, raccoon, and domestic cat, are also active diggers.

Our Invasion Genesis Hypothesis…

The burrow dug by the typical commensal rodent is too narrow for most of their predators to enter. As long as those predators don’t go to the trouble to dig their burrows up, they and their young are safe in their subterranean redoubts. It would be foolish, however, for any burrowing rodent to behave as though its subterranean nest was forever beyond the reach of their predators. In the process of living, eating, urinating, and defecating, burrowing rodents produce strong odors that enable their predators to sniff them out. If sufficiently hungry, and food is scarce, such predators eagerly dig up the burrows their noses discover, in hopes of reaching the rodent’s progeny.

Today’s adult burrowing rodents are almost never seriously endangered by the predators that dig up their nests. Over the millions of years during which they’ve evolved (rodent fossils date to the the Paleocene epoch, between 56-66 million years ago), rodents have assembled a number of defensive behaviors that aid their escape from would-be predators. Alas, but the same cannot be said for their young, and in fact most burrowing rodents take advantage of the fact that the young in their subterranean nests provide an excellent means of protecting the adults from harm. Soon after the typical burrowing rodent first digs its primary burrow and establishes its subterranean redoubt, it takes the added step of preparing an escape burrow to be used when predators begin to dig up the primary one. That auxiliary burrow exits some distance away, usually in a place that is more difficult for predators to access.

On discovering the primary rodent burrow (Fig. 12) at this home, a diligent search was conducted to find the escape burrow associated with it. That search was not successful. Was this particular rodent too lazy to build one? That’s unlikely. Its life depended on it, so it was almost certainly present. But where? The only place we could not search was inside the crawl space, so it can be safely inferred that the auxiliary burrow emerged from the soil there. But why inside the crawl space? Did the rodent know the crawl space was there? Surely not, for reasons previously discussed. Why, then, would the burrowing rodent choose to have its escape burrow emerge somewhere beyond what, according to all available evidence, was a solid concrete foundation?

Why under a home’s foundation?

Millions of years ago, when rodents first began building burrows in soil that had recently been trod by dinosaurs and would, in a few more million years, host saber-toothed cats, there were no man-made concrete foundations next to which they might nest. But there was an abundance of boulders, which to today’s rodent’s eyes are analogous to a home’s concrete foundation. Would ancient rodents have benefited by building their primary burrows next to such boulders, then have their escape burrows emerge underneath them? To answer that we must first imagine what the rodent might find when the escape burrow reached the underside of such a boulder.

At the very least they’d find a sturdy, impenetrable roof, one that predators would not be able to access. If by chance, the soil mated perfectly with the boulder, the rodent could compact it somewhat to form a room or to build more burrows directly under the rock. More often than not, however, they would find small pockets of enclosed, open space, where the soil had not mated perfectly to the underside of the boulder. There, within the confines of such confined pockets, they could — without needing to expend additional energy to enlarge the space — relax in comparative safety until the predator was gone.

That predator, on reaching the rodent’s subterranean nest, would consume the nesting young, then go on its way, sniffing out some of the other primary burrows that might be found nearby. It would not be able to reach the rodent’s escape burrow under the boulder without investing more energy than the rodent was worth, so the rodent was safe, at least for the moment.

Today, the monolithic slab foundations under most modern homes have identical pockets of open space, where — almost immediately after the home is constructed — the soil has contracted, pulling away from the underside of the slab. Homes on pier and beam foundations provide crawlspaces that, to the rodent, serve similar if not even more attractive purposes. So, placing a primary burrow next to a large rock, or a home’s concrete foundation, and then building an escape burrow that emerges under the rock or foundation, is a good recipe for the burrowing rodent’s survival. And that, I postulate, is most likely what this rodent did.

So, now the adult rodents have escaped their predator, sacrificing to its appetite the non-ambulatory young in their nest. Afterward, though, the relatively large hole the predator excavated remained open to inspection by other predators, and the rodent’s old redoubt has been violated. What might you suppose would happen next?

What happens next…

At the bottom of that excavated hole are found nesting materials, tainted by a cacophony of strong odors from the urine and fecal pellets left behind by the rodents that built the nest. Those odors are later replenished, as the rodents continue to use the auxiliary burrow as a means to come and go from the crawl space, or from the cavity under a monolithic slab. Therein, nesting is safer, more spacious, and provides a host of places to hide and nest in, so additional burrowing is unnecessary. The rodent surveys the open space afforded underneath the rock, the foundation, or in the crawl space, then selects the safest place there to build a new birthing nest, and life goes on as before.

As more predators visit the site, they are attracted to the excavated hole. Over time they proceed to enlarge and lengthen it, in hopes of reaching another nest of young. Eventually these predators extend the excavation upward along the path taken by the auxiliary burrow. Finally — weeks, months, or even years after the primary burrow was excavated by the initial predator — the exit port to the surface, at the terminus of the escape burrow, is breached. Then, voila! They, too, become beneficiaries of whatever spacious, safe, and darkened environ the area beyond that terminus provides.

How to stop new wild animal invasions from starting…

The caption to Figure 13, above, alludes to eight steps that often lead to wild animal incursions into the crawlspace voids of residential and commercial structures. These steps are listed below:

  1. Abundant harborage, suitable for rodents to hide, nest, and thrive in, exists in the landscape;
  2. The abundant rodent harborage in a site’s landscape permits large numbers of rodents to live and forage there;
  3. The resulting endemic rodent population attracts predators such as feral cats, skunks, raccoons, foxes, predatory rodents, and opportunistic omnivores such as opossums;
  4. The presence of large populations of rodent predators reduces populations of terrestrial rodents, and increases populations of rodents that are active burrowers;
  5. High populations of actively burrowing rodents increases the probability that one or more of them will burrow into the soil next to the foundation of a structure on that site;
  6. Rodent burrows adjacent to a foundation encourage incursions by predators that are active diggers, such as foxes, that are likely, at some time in the future, to mount a concerted effort to excavate the rodent burrows they find in order to reach the young within their subterranean nests;
  7. Threatened rodents will escape through auxiliary burrows that generally are built to emerge under the structure’s foundation, allowing entry therefrom into the structure’s crawlspace; and
  8. The excavating predator and those that follow it will, over time, continue to excavate the rodent’s burrow, all along its length, eventually creating a moderately large pathway into the structure’s crawlspace that can then be exploited by a variety of other wild animals.

Read over these eight steps carefully. Then mentally eliminate the precursory step from which the sequence proceeds. In other words, remove those conditions that allow for large numbers of rodents to become endemic in the home’s landscaping. Once that is done, the rest of the sequence is moot. Absent that first step — i.e., the active presence of abundant rodent harborage — the likelihood that the remaining steps will occur in sequence diminishes to near zero.

So, the simplest way to prevent wild animals from nesting under our homes is to stop rodents from nesting there. And the simplest way to stop rodents from thriving in our yards and gardens is to eliminate all rodent harborage, i.e., the places where they are able to construct cryptic nests. At this site, that meant removing, or at least substantially reducing, the landscape’s ground cover and vines.

The front yard…

This was discussed with the homeowners and they immediately began to make significant modifications to the landscape architecture of the front yard. Over the next several months impressive changes were made, including taking up all the vines and botanical ground covers that impinged on the structure, installing pavers in those same areas to inhibit future plant growth, and clearing the dense undergrowth from beneath shrubbery. It was a lot of work, but they enjoyed the exercise and other health benefits of being outside and, on a warm to hot summer day in Texas, breaking a good sweat.

Besides keeping the rat and mouse populations down, the modifications they made also benefited the home’s masonry exterior. Vines do significant damage to masonry walls, not only by inserting root-like tendrils into masonry cracks and crevices, but by providing a microenvironment that fosters the development of fungi, mold, and mildew. That damage was brought to a halt by removing the vines and their tendrils.

The backyard landscape at this home, on the other hand, had been designed and developed over a long period of time, and was now exactly as the homeowners wanted it. Modifying that was out of the question, but they were open to alternative solutions.

What to do when removing harborage is out of the question...

It was made clear to these homeowners that the most promising alternate means of preventing rodents from colonizing the back yard involved the installation of rodent bait stations.

Though rodent bait stations provide an excellent way to keep rodent populations in check, they are — nevertheless — short of ideal for a host of reasons. They must first be properly placed, then inspected, maintained, and re-provisioned with bait on a regular basis. That isn’t as simple as it seems, and few — even within the pest management industry — realize the full extent of what those tasks entail.

The negative side of rodent bait stations…

Rodent bait becomes easily contaminated with excessive moisture, rendering it unpalatable. Snails and slugs are attracted to rodent bait and deposit trails of gastropod slime over bait surfaces that render them unsavory. Most rodent baits intended for professional use are weatherized, with paraffin, to extend their life in unfriendly environments; excessive heat, however, will melt paraffin bait blocks, making them less tasty. Exposure to air for more than three months, even in temperature-controlled environments, causes the volatile attractants in the blocks to evaporate, rendering them stale; many rodents will pass stale blocks by in favor of the seeds and vegetable matter than make up most of their natural diet. Thus, for all the forgoing reasons, it is common for bait stations that appear to be fully provisioned to have lost much, if not most, of their functionality.

To ensure that all the bait stations installed at a given site are fully functional, they should each be cleaned of existing bait and contaminants, and re-provisioned with fresh bait, every three months or less. If this is not done, the bait stations will not prevent a fresh, endemic rodent population from arising. That nascent rodent population will then attract, to the site, all the wild animals that prey on them. Incursions of the newly endemic rodents, into all the accessible voids within the structures at the site, will eventually take place. And, of course, all the conditions that led, earlier, to the invasion of this home’s crawlspace by wild animals, will soon come into play once more, placing the voids of this residence at risk of invasion by the wild animals that prey on rodents.

Most rodent bait station placements are not as functional as they may appear…

The proper installation, maintenance, and provisioning of rodent bait stations, even in a relatively small residential yard, is not a trivial exercise. Doing it right is a nasty, cumbersome, and time consuming job. Few pest management personnel are willing to take the time needed to conduct the step-by-step procedures required. Those who are willing to do so soon discover that most of their clients are unwilling to compensate them in a manner commensurate with the tedium, nastiness, time, and effort required to do the job right. That, more than anything else, discourages good maintenance practices.

From the perspective of the client, it is hard to understand why they should pay a premium to have their rodent bait stations specially maintained. After all, most pest management firms promise to place and maintain bait stations in residential yards, as a part of their normal pest management contract, often at little or no extra cost. Of course, since they are not being paid much to maintain the bait stations, they have little incentive to do so and… well… you know the rest.

So, a charade takes place that continues for as long as it takes before a major calamity (like rats inside the home, or wild animals invading an attic or a crawlspace) occurs. It may take months or even years before the homeowner is even aware that their home is under invasion, but during that time, from all outward appearances, the inspection, maintenance, and re-provisioning of the installed bait stations at their site has taken place on every treatment visit. The homeowner has no reason to believe otherwise. The stations cannot be inspected without using a special key, so the homeowner cannot check up on things even if they wanted to (and who would want to?). So, though little or nothing is being done to maintain the functionality of the bait stations in place, the homeowner hasn’t a clue.

And now, the positives…

Properly placed, well-maintained bait stations of advanced design do an excellent job of preventing endemic rodent populations from developing at the site where they are placed.

The newest bait station designs protect the baits they contain from excessive moisture contamination. Even those of the best construction, however, must be fully decontaminated, cleaned, and filled with fresh bait every three months or less. Unless this is done, their functionality is of short duration.

The importance of keeping rodent populations in check cannot be overstated…

Preventing endemic rodent populations in a home’s landscape has an important, cascading effect. Every angle of that effect is beneficial to the home, its human inhabitants, and their companion pets. Don’t fall for the idea that your cats will keep the rats and mice in check. Most of the time they won’t. In those cases where they do, they do so at a heavy price. Rodents and their parasites help spread disease (according to the CDC, a total of 35 serious diseases are spread by rodents), including murine typhus, tularemia, salmonellosis, rat-bite fever (Streptobacillus moniliformis), leptospirosis, lymphocytic Chorio-meningitis, plague, and hantavirus. Often the victims of these diseases have no idea how they became infected, so no efforts are taken to prevent future infections.

The number of wild animal forays into residential yards and landscapes diminishes markedly in the absence of rodent prey. Subsequently, the presence of harmful mites, ticks, fleas, and the multitude of annoying and potentially dangerous ecto-and-endoparasites that fall from, are brushed from, or that jump from the bodies of wild animals during foraging visits, as well as those that are deposited on the ground in wild animal scat, will decline as well…

Appendix A: Taxonomy (Family Trees of Specific Organisms) — Note that on-going advances in DNA sequence analyses, retrotransposon presence or absence data, and the debates such advances engender within the scientific community, are presently muddying the waters of the taxonomical world. At the heart of this chaotic atmosphere is the transition taking place between traditional Linnaean taxonomical designations, based on anatomical characters, and cladistic nomenclature based on genomic characters. Until this transition is settled by the adoption of a uniform and widely accepted nomenclature any effort to list the taxonomy of a given organism will necessarily include designations that are in dispute. The list that follows reflects that necessity.

  • Kingdom Animalia (ahn-uh-MAYHL-yuh) — first described in 1758 by the Swedish taxonomist Carolus Linnaeus (23 May 1707 – 10 January 1778), using the Latin word animal = “a living being,” from the Latin word anima = “vital breath”, to refer to multicellular, eukaryotic organisms whose body plans become fixed during development, some of which undergo additional processes of metamorphosis later in their lives; most of which are motile, and thus exhibit spontaneous and independent movements; and all of whom are heterotrophs that feed by ingesting other organisms or their products;
  • Phylum Chordata (kohr-DAY-tuh) — animals that have, at some point in their life cycle, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail.
  • Clade Craniata (kray-nee-AH-tuh) — a clade of chordate animals that contains, as living representatives, the Myxini (hagfish), Petromyzontida (including lampreys), and Gnathostomata (jawed vertebrates); craniates are animals with a hard skull, of bone or cartilage, in the phylum Chordata.
  • Subphylum Vertebrata (vurr-tuh-BRAY-tuh) — chordate animals with backbones and spinal columns;
  • Infraphylum Gnathostomata (nah-thow-stoh-MAW-tuh) — the jawed vertebrates; derived from the Greek nouns γνάθος (gnathos) = “jaw” + στόμα (stoma) = “mouth”; comprised of some 60,000 species, i.e., 99% of all living vertebrates; living gnathostomes also have teeth, paired appendages, and a horizontal semicircular canal of the inner ear, with other physiological and cellular anatomical characters such as myelin-sheathed neurons, and an adaptive immune system that utilizes V(D)J recombination, rather than genetic recombination in the variable lmyphocyte receptor gene, to create antigen recognition sites; it is presently believed that Gnathostomata evolved from ancestors that already possessed a pair of both pectoral and pelvic fins;
  • Clade Eugnathostomata (yew-NAH-thow-stoh-mah-tuh) — the Chondrichthyes (cartilaginous fishes), and the
    Osteichthyes (bony fishes);
  • Clade Osteichthyes (oss-tee-ICK-thee-eez) [Huxley, 1880] — the bony fish; a diverse taxonomic group of fish with skeletons primarily composed of bone tissue, as opposed to cartilage; most fish are members of Osteichthyes, a diverse group of 45 orders, 435 families and 28,000 species comprising the largest class of vertebrates presently recognized; divided into ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii); oldest known fossils of bony fish are about 420 million years old and are transitional fossils that display a tooth pattern between that of the tooth rows of sharks and bony fishes; in comparison to Euteleostomi, in paleontological terms, the terms are synonymous; in ichthyology, the Euteleostomi presents a cladistic view which includes the terrestrial tetrapods that evolved from lobe-finned fish, whereas on a traditional view, Osteichthyes includes only fishes and is therefore paraphyletic; however, recently-published phylogenetic trees treat the Osteichthyes as a clade;
  • Superclass Tetrapoda (teh-trah-POH-duh) — derived from the ancient Greek expression τετραπόδηs = “four-footed” and comprised of the first four-limbed vertebrates and their descendants, including living and extinct amphibians, birds, mammals, reptiles and some ancient, exclusively aquatic creatures such as the Acanthostega; evolved from the lobe-finned fishes around 390 million years ago in the middle Devonian Period; modern tetrapod groups appeared by the late Devonian, 367.5 million years ago; specific aquatic ancestors of the tetrapods, and the processes leading to land colonization, remain unclear; most present species are terrestrial but the first tetrapods were fully aquatic; most present amphibians are semiaquatic and live the first stage of life as fish-like tadpoles; amniotes evolved about 340 million years ago (crown amniotes 318 mya), and their descendants are believed to have driven most amphibians to extinction; one population of amniotes diverged into lizards, dinosaurs, birds and their relatives, while another diverged into mammals and their extinct relatives; several groups of tetrapods, such as the caecilians, snakes, cetaceans, sirenians, and moas have lost some or all of their limbs; many tetrapods have returned to partially aquatic or fully aquatic lives; the first returns to an aquatic lifestyle may have occurred during the Carboniferous Period; the change from a body plan for breathing and navigating in water to a body plan enabling the animal to move on land is one of the most profound evolutionary changes known;
  • Clade Reptiliomorpha (repp-till-ee-oh-MOR-fuh) [Säve-Söderbergh, 1934] — proposed by Professor Gunnar Säve-Söderbergh in 1934 to designate amniotes and various types of late Paleozoic tetrapods more closely related to amniotes than to living amphibians, based on the belief that amphibians had evolved from fish twice, one group composed of the ancestors of modern salamanders, the other — which Säve-Söderbergh referred to as Eutetrapoda — comprising the anurans (frogs), amniotes and their ancestors, with the origin of caecilians being uncertain. Säve-Söderbergh’s Eutetrapoda consisted of two sister-groups: Batrachomorpha, containing anurans and their ancestors, and Reptiliomorpha, containing anthracosaurs and amniotes; he subsequently added Seymouriamorpha to his Reptiliomorpha as well; Alfred Sherwood Romer rejected Säve-Söderbergh’s theory of a biphyletic amphibia and used Anthracosauria to describe the labyrinthodont lineage from which amniotes evolved; un 1970, the German paleontologist Alec Panchen took up Säve-Söderbergh’s name for this group as having priority, but Romer’s terminology is still in use; some writers preferring phylogenetic nomenclature use Anthracosauria;
  • Clade Amniota (amm-nee-OH-tuh) [Haeckel, 1866] — from Greek ἀμνίον (AMM-nee-awn) = “membrane surrounding the fetus”, and with an earlier meaning of “(the) bowl in which the blood of sacrificed animals was caught”, from ἀμνός (AMM-nos) = “lamb”; a clade of tetrapod vertebrates comprised of reptiles, birds, and mammals that lay eggs on land or retain fertilized eggs within the mother’s body; distinguished from anamniotes (fishes and amphibians) that typically lay eggs in water; include synapsids (mammals along with their extinct kin) and sauropsids (reptiles and birds), as well as their ancestors; amniote embryos are protected by extensive membranes; in eutherian mammals such as humans, these membranes include the amniotic sac that surrounds the fetus; embryonic membranes and the absence of a larval stage distinguish amniotes from tetrapod amphibians; first or “basal” amniotes resembled small lizards and evolved from the amphibian reptiliomorphs about 312 million years ago in the Carboniferous period; their eggs could survive out of the water, allowing amniotes to expand into drier environments; the eggs could also “breathe” and cope with wastes, allowing the eggs and the amniotes themselves to evolve into larger forms;
  • Clade Synapsida (suh-NAPP-suh-duh) [Osborn, 1903] — the synapsids (from the Greek expression meaning ‘fused arch’), are synonymous with the theropsids (from the Greek expression meaning ‘beast-face’), and include both mammals and every other animal that is more closely related to mammals than to other living amniotes; distinguished from other amniotes by the presence of a temporal fenestra, or opening, low in the skull roof behind each eye having a bony arch beneath each eye that first appeared in the Late Carboniferous period, 312 million years ago, and accounts for the designation; primitive synapsids are often referred to as pelycosaurs or pelycosaur-grade synapsids, while more advanced mammal-like synapsids are referred to as therapsids; the non-mammalian members are described as mammal-like reptiles in classical systematics, and are often called stem mammals or proto-mammals; synapsids evolved from basal amniotes and comprise one of the two major groups of the later amniotes, the other being the sauropsids, which comprises the modern reptiles and birds; synapsids were the largest terrestrial vertebrates in the Permian period, 299 to 251 million years ago, though some of the larger pareiasaurs, appearing at the end of Permian period, matched their size;
  • Clade Eupelycosauria (yew-puh-lee-koh-SAW-ree-uh) [Kemp, 1982] — originally used to refer to a suborder of ‘pelycosaurs’ (Reisz 1987), but presently used (see Laurin and Reisz 1997) to designate a clade of synapsids that includes most pelycosaurs, as well as all therapsids and mammals; first appeared during the Early Pennsylvanian epoch (e.g., Archaeothyris, and an earlier genus, Protoclepsydrops), and represent a stage in the acquisition of mammal-like characteristics (Kemp 1982), in contrast to their earlier amniote ancestors; defining characteristics separating these animals from the Caseasauria (also pelycosaurs) are based on proportional dimensioning of certain bones of the skull, including a long, narrow supratemporal bone that contrasts with caseasaurs where the width of the supratemporal bone is almost as great as its length, and a frontal bone that widely connects to the upper margin of the orbit (Laurin and Reisz 1997);
  • Clade Sphenacodontia (sfenn-uh-coh-DON-tee-uh) — a stem-based clade of derived synapsids defined by Amson and Laurin (2011) as “the largest clade that includes Haptodus baylei, Haptodus garnettensis and Sphenacodon ferox, but not Edaphosaurus pogonias”; they first appear during the Late Pennsylvanian epoch; basal Sphenacodontia constitute a transitional evolutionary series from early pelycosaurs to ancestral therapsids, ancestors of more advanced forms and mammals, thus sometimes referred to as proto-therapsids;
  • Clade Sphenacodontoidea (sfenn-uh-coh-don-TOY-dee-uh) — a node-based clade defined to include the most recent common ancestor of the Sphenacodontidae and the Therapsida, along with their mammalian and non-mammalian descendants; distinguished in accord with a number of specialized characteristics concerning proportional dimensioning of bones of the skull and of the teeth; evolved from earlier Sphenacodontia such as Haptodus via a number of transitional stages of small, unspecialized pelycosaurs;
  • Clade Therapsida (thuh-RAPP-suh-duh) [Broom, 1905] — a group of synapsids, including mammals and their ancestors; many traits today seen as unique to mammals had their origin within early therapsids, including having their four limbs extend vertically beneath the body, as opposed to the sprawling posture of other reptiles; earliest fossil attributed to Therapsida is Tetraceratops insignis from the Lower Permian; evolved from pelycosaurs (specifically sphenacodonts) 275 million years ago; replaced the pelycosaurs as the dominant large land animals in the Middle Permian; replaced by the archosauromorphs in the Triassic; the therapsids include the cynodonts, the group that gave rise to mammals in the Late Triassic around 225 million years ago; of non-mammalian therapsids, only cynodonts and dicynodonts survived the Triassic–Jurassic extinction event; the last of the non-mammalian therapsids, the tritylodontid cynodonts, became extinct in the Early Cretaceous, approximately 100 million years ago;
  • Clade Eutherapsida (yew-thuh-RAPP-suh-duh)
  • Clade Neotherapsida (nee-oh-thuh-RAPP-suh-duh) [Hopson, 1999] — a clade of therapsids, that includes anomodonts and the more derived theriodonts, which include mammals;
  • Clade Theriodontia (thee-ree-oh-DON-tee-uh)[Owen, 1876] — derived from ancient sources meaning “Beast Tooth”, a reference to the more mammal-like teeth displayed by the animals comprising this major group of therapsids; when defined in traditional, Linnaean terms, they form a suborder of mammal-like reptiles that lived from the Middle Permian to the Middle Cretaceous; when defined in cladistic terms, they include traditional theriodonts and their mammalian descendants; appeared at about the same time as the anomodonts, some 265 million years ago in the Middle Permian;
  • Clade Eutheriodontia (yew-thee-ree-oh-DON-tee-uh) [Hopson & Barghusen, 1986] — a clade of therapsids, erected by Hopson & Barghusen in 1986, that includes therocephalians and cynodonts; the close relationship between therocephalians and cynodonts has been recognized for many years, as they are thought to have diverged in the Middle Permian, and each group independently evolved mammal-like features, including a secondary palate and the loss of the postorbital bar, both of which were retained in mammals, which are considered a derived group of cynodonts; mammalian features that both groups inherited from a common ancestor include loss of teeth on the palate, expansion of the epipterygoid bone at the base of the skull, and narrowing of the skull roof to a narrow sagittal crest running between large temporal openings;
  • Clade Cynodontia (sinn-oh-DON-tee-uh) [Owen, 1861] — therapsids with “dog teeth” that first appeared in the Late Permian, some 260 million years ago; includes modern mammals, including humans, as well as their extinct ancestors and close relatives; non-mammalian cynodonts spread throughout southern Gondwana and are represented by fossils from South America, Africa, India, and Antarctica; in northern continents, fossils have been found in eastern North America as well as in Belgium and northwestern France; one of the most diverse groups of therapsids;
    Clade Mammaliamorpha (muh-may-lee-uh-MOHR-fuh) — the clade originating with the last common ancestor of Tritylodontidae and the crown group mammals, and as such a wider group than mammaliaformes, such that it includes some families that trait-based taxonomy does not include in Mammalia, in particular Tritylodontidae and Brasilodontidae;
  • Clade Mammaliaformes (muh-may-lee-uh-FOR-mees) [Rowe, 1988] — a clade containing the crown group mammals and their closest extinct relatives; the group, which radiated from earlier probainognathian cynodonts, is defined as the clade originating from the most recent common ancestor of Morganucodonta and the crown group mammals; the latter is the clade originating with the most recent common ancestor of extant Monotremata, Marsupialia, and Placentalia; besides Morganucodonta and the crown group mammals, it includes Docodonta and Hadrocodium as well as the Triassic Tikitherium, the earliest known member of the group; Mammaliaformes is a term of phylogenetic nomenclature; by contrast, the assignment of organisms to Mammalia has traditionally been founded on traits and, on this basis, Mammalia is slightly more inclusive than Mammaliaformes; trait-based taxonomy generally includes Adelobasileus and Sinoconodon in Mammalia, though they fall outside the Mammaliaformes definition;
  • Class Mammalia (muh-MAIL-yuh) [Linn. 1758] — from the Latin noun mamma = “breast”, a clade of endothermic amniotes distinguished from reptiles and birds by the possession of a neocortex region in the brain, hair, three middle ear bones and mammary glands; includes the largest animals on the planet, the great whales, as well as some of the most intelligent, such as elephants, primates and cetaceans; basic body type is a terrestrial quadruped, but some mammals are adapted for life at sea, in the air, in trees, underground or on two legs; the largest group of mammals have a placenta, which enables the feeding of the fetus during gestation; mammals range in size from the 30–40 mm (1.2–1.6 in) bumblebee bat to the 30-meter (98 ft) blue whale; except for the five species of monotreme (egg-laying mammals), all modern mammals give birth to live young; most mammals, including the six most species-rich orders, belong to the placental group; the three largest orders in number of species are Rodentia: mice, rats, porcupines, beavers, capybaras and other gnawing mammals; Chiroptera: bats; and Soricomorpha: shrews, moles and solenodons; the next three biggest orders, depending on the biological classification scheme used, are the Primates including the great apes and monkeys; the Cetartiodactyla including whales and even-toed ungulates; and the Carnivora which includes cats, dogs, weasels, bears and seals;
  • Magnorder Boreoeutheria (boh-ree-oh-yew-THEE-ree-uh) — from the Greek noun βόρειο = “north” + the Greek adjective ευ = “good” + the Greek noun θεριό = “beast”; a magnorder, which the International Code of Zoological Nomenclature (ICZN) uses to designate a clade of unusually important significance, of placental mammals comprised of the sister taxa Laurasiatheria (most hoofed mammals, most pawed carnivores, and several other groups) and Euarchontoglires (Supraprimates); this magnorder is now well supported by DNA sequence analyses, as well as retrotransposon presence or absence data; the earliest known fossils belonging to this magnorder date to about 65 million years ago, shortly after the K-Pg extinction event, though molecular data suggests they may have originated earlier, during the Cretaceous period; with the exception of rhinoceroses and cetaceans, male members of the clade share the distinction of external testicles
  • Superorder Laurasiatheria (larr-ay-shuh-THEE-ree-uh) — a superorder of placental mammals that originated on the northern supercontinent of Laurasia some 99 million years ago, and that includes shrews, pangolins, bats, whales, carnivorans, odd-toed and even-toed ungulates, among others; Laurasiatheria was founded on the basis of the similar gene sequences, and retrotransposon presence or absence data, that are shared by the mammals that belong to it; as no anatomical features have yet been found that unite the group, Laurasiatheria is a clade, without a Linnaean rank, but with the cladistic rank of superorder; the name reflects the theory that these mammals evolved on the supercontinent of Laurasia, after it split from Gondwana when Pangaea broke up; it is a sister group to Euarchontoglires (or Supraprimates) with which it forms the clade Boreoeutheria;
  • Clade Scrotifera (skrow-TIFF-er-uh) — a proposed clade of mammals within Laurasiatheria, consisting of six orders and their common ancestors, arranged within the two subgroups Chiroptera (the bats) and Ferungulata; the name derives from the word scrotum, a pouch in which the testes permanently reside in the adult male; thus all members of the group have a postpenile scrotum, often prominently displayed, except for some aquatic forms and pangolin (for which the testes lie just below the skin); it appears to be an ancestral character for this group, yet other orders generally lack this as an ancestral feature, with the probable exception of Primates;
  • Clade Ferungulata (feer-un-gew-LAH-tuh) — a traditional clade within the cohort of placental mammals; established by George Gaylord Simpson in 1945, it includes the extant Carnivora, Perissodactyla and Artiodactyla as well as Tubulidentata and a superorder, Paenungulata, plus a number of orders known only as fossils; though Simpson placed whales (Cetacea) in a separate cohort, recent evidence linking them to Artiodactyla would mean that they belong here as well; Simpson established the grouping on the basis of morphological criteria, but this traditional understanding of Ferungulata has been challenged by a more recent classification, relying upon genetic criteria, in which his ferungulate orders are divided between two distinct cohorts, Afrotheria and Laurasiatheria; advocates of this newer system redefine Ferungulata as a clade within Laurasiatheria, comprising the larger portion of the former Ferungulata and including ‘true’ ungulates (Perissodactyla and Artiodactyla), whales and Carnivora, with the addition of pangolins (Pholidota), but excluding Tubulidentata and paenungulates; a newer clade name, Scrotifera, described above, has thus been proposed;
  • Clade Pegasoferae (pegg-uh-soh-FEER-ee) — a proposed clade of mammals based on genomic research in molecular systematics by Nishihara, Hasegawa and Okada; to the surprise of the authors, their data led them to propose a clade that includes bats (order Chiroptera), carnivores such as cats and dogs (order Carnivora), horses and other odd-toed ungulates (order Perissodactyla) and pangolins (order Pholidota) as springing from a single evolutionary origin within the mammals; the name Pegasoferae was coined from the name of the mythological flying horse Pegasus to refer to bats and horses, and the term Ferae, encompassing carnivorans and pangolins; according to this, the odd-toed ungulates’ closest living relatives are the carnivorans; earlier theories of mammalian evolution have aligned bats with the insectivores (order Eulipotyphla) and horses with the even-toed ungulates (order Artiodactyla); some subsequent molecular studies published shortly afterwards have failed to support the authors’ conclusions, in particular, two recent studies, each combining genome-wide analyses of multiple taxa with testing of competing alternative phylogenetic hypotheses, conclude that Pegasoferae is not a natural grouping;
  • Clade Zooamata (zoh-ah-MAH-tuh) — a clade of mammals consisting of Ferae (carnivores and pangolins) and Perissodactyla (odd-toed ungulates); together with Cetartiodactyla (even-toed ungulates and whales) and chiroptera (bats) it forms Scrotifera (formerly Ferungulata), and is part of Laurasiatheria; the name is constructed from Greek and Latin to mean “animal friends”, a reference to the inclusion of cats, dogs, and horses; a conflicting proposal links the Perissodactyla and Cetartiodactyla in a clade named Euungulata; both proposals are based on molecular evidence, but neither of these clades is fully supported;
  • Clade Ferae (FEER-ee) — a clade of mammals, consisting of the orders Carnivora (over 260 species worldwid) and Pholidota (eight species of pangolins in tropical Africa and Asia); pangolins do not look much like carnivorans (wolves, cats, seals, and so on), and were thought to be the closest relatives of Xenarthra (armadillos, sloths, and so on), but recent DNA research found a close relationship to carnivorans; Ferae were also thought to include Creodonta, extinct primitive carnivoran-like mammals, but it turned out to be a polyphyletic assemblage of unrelated mammal groups; several extinct orders, relatives of Pholidota, are members of the Ferae, as well; an alternate name, Ostentoria, has also been proposed for a grouping of the Carnivora and Pholidota; according to recent studies the closest relatives of Ferae are Perissodactyla (horses, tapirs, and rhinos) and Cetartiodactyla (which combines Artiodactyla—camels, pigs, ruminants and hippos—with Cetacea—whales and dolphins); an alternate phylogeny (less supported) holds that the closest relatives to the Ferae are the Perissodactyla and Chiroptera (bats), not Cetartiodactyla; Ferae together with Perissodactyla has been called Zooamata. Ferae, Perissodactyla, and Chiroptera together has been called Pegasoferae;
  • Clade Carnivoramorpha (kar-nih-vor-ah-MOR-fuh) — a clade of mammals that includes the modern order Carnivora, but that also includes a paraphyletic superfamily that had been traditionally divided into two families of carnivores: Miacidae (the miacids) and Viverravidae; Miacoids were primitive carnivores that lived during the Paleocene and Eocene Epochs, about 33-66 million years ago; today Miacidae is recognized as a paraphyletic array of stem taxa that probably resulted in some “miacid” genera ending up just outside the order Carnivora, the crown-group within the Carnivoramorpha. Carnivoramorpha consists of both Miacoidea and Carnivora, but excludes the order Creodonta that existed alongside Carnivoramorpha; Miacoids are regarded as basal carnivoramorphs; the miacids are a paraphyletic group containing all miacoids that are not viverravids; the transition from miacids to Carnivora was a gradual trend during the Paleocene to late Eocene, with taxa from both North America and Eurasia involved; the miacids did not appear until the very end of the Paleocene and are characterized by their shorter skull, and loss of contact between the calcaneum and fibula in the ankle; Miacoids were mostly small carnivores superficially reminiscent of martens or civets. They probably fed on invertebrates, lizards, birds and smaller mammals like shrews and opossums, while others may have been insectivores. Some species were arboreal, others lived on the ground. Their teeth and skull show that the miacoids were less developed than modern carnivores.
  • Order Carnivora (kar-NIH-vor-uh) [Bowdich, 1821] — from Latin carō = “flesh”, + vorāre “to devour”); a diverse order comprised of more than 280 species of placental mammals whose members are referred to as carnivorans, whereas the word “carnivore”, which is often popularly applied to members of this group, can more broadly refer to any meat-eating organism; carnivorans are more diverse in size than any other mammalian order; members range from the least weasel (Mustela nivalis), weighing in at 25 g (0.88 oz) and sized at 11 cm (4.3 in) in length, to the polar bear (Ursus maritimus), which can weigh up to 1,000 kg (2,200 lb), to the southern elephant seal (Mirounga leonina), whose adult males weigh up to 5,000 kg (11,000 lb) and measure up to 6.9 m (23 ft) in length; some carnivorans, such as cats and pinnipeds, depend entirely on meat for their nutrition; others, such as raccoons and bears, depending on the local habitat, are more omnivorous: the giant panda is almost exclusively a herbivore, but will take fish, eggs and insects, while the polar bear subsists mainly on seals; carnivorans have teeth and claws adapted for catching and eating other animals; many carnivorans hunt in packs and are social animals, giving them an advantage over larger prey;
  • Family Procyonidae (pro-see-AWN-nuh-dee) — a New World family of the order Carnivora that includes the raccoons, coatis, kinkajous, olingos, olinguitos, ringtails and cacomistles; procyonids inhabit a wide range of environments and are generally omnivorous, and are relatively small animals, with generally slender bodies and long tails (though the common raccoon tends to be bulky); many procyonids have banded tails, and distinctive facial markings; like bears, procyonids are plantigrade, walking on the soles of their feet; most species have non-retractile claws; because of their general build, the Procyonidae are often popularly viewed as smaller cousins of the bear family; this is reflected in their German names: a raccoon is called a Waschbär (washing bear, as he “washes” his food before eating), a coati is a Nasenbär (nose-bear) while a kinkajou is a Honigbär (honey-bear); the Dutch follow suit, calling the animals wasbeer, neusbeer and rolstaartbeer respectively; however, it is now believed that procyonids are more closely related to mustelids than to bears; due to their omnivorous diet, procyonids have lost some of the adaptations for flesh-eating found in their carnivorous relatives; while they do have carnassial teeth, these are poorly developed in most species, especially the raccoons;
  • Genus Procyon (PRO-see-awn) — a genus of nocturnal mammals, comprising three species commonly known as raccoons, in the family Procyonidae; the most familiar species, the common raccoon (P. lotor), is often known simply as “the” raccoon, as the two other raccoon species in the genus are native only to the tropics and less well known; genetic studies have shown that the closest relatives of raccoons are the ring-tailed cats and cacomistles of genus Bassariscus, from which they diverged about 10 million years ago;
  • Species Procyon lotor (pro-see-awn LOH-torr) — the raccoon, sometimes spelled racoon, is also known as the common raccoon, North American raccoon, northern raccoon, and colloquially as coon, is a medium-sized mammal native to North America. The raccoon is the largest of the procyonid family, having a body length of 40 to 70 cm (16 to 28 in) and a body weight of 3.5 to 9 kg (8 to 20 lb). Its grayish coat mostly consists of dense underfur which insulates it against cold weather, two of the raccoon’s most distinctive features are its extremely dexterous front paws and its facial mask, which are themes in the mythology of several Native American ethnic groups; raccoons are noted for their intelligence, with studies showing that they are able to remember the solution to tasks for up to three years; the diet of the omnivorous raccoon, which is usually nocturnal, consists of about 40% invertebrates, 33% plant foods, and 27% vertebrates; the original habitats of the raccoon are deciduous and mixed forests, but due to their adaptability they have extended their range to mountainous areas, coastal marshes, and urban areas, where some homeowners consider them to be pests; as a result of escapes and deliberate introductions in the mid-20th century, raccoons are now also distributed across mainland Europe, Caucasia, and Japan; though previously thought to be solitary, there is now evidence that raccoons engage in gender-specific social behavior; related females often share a common area, while unrelated males live together in groups of up to four animals to maintain their positions against foreign males during the mating season, and other potential invaders; home ranges vary from 3 hectares (7.4 acres) for females in cities to 5,000 hectares (12,000 acres) for males in prairies; after a gestation period of about 65 days, two to five young, known as “kits”, are born in spring; the kits are subsequently raised by their mother until dispersal in late fall. Although captive raccoons have been known to live over 20 years, their life expectancy in the wild is 1.8 to 3.1 years; in many areas, hunting and vehicular injury are the two most common causes of death.

Appendix B: Listing of all the Known Arboreal, Terrestrial, and Burrowing Rodents found in Central Texas.

The nearly 2,000 species of rodents that are presently recognized worldwide comprise about 40% of all living mammals. 68 rodent species are known to be found in Texas, and 24 of these are found in Central Texas, all fully capable of invading yards, landscapes, and man-made structures.

Rodents are distinguished from other mammals by the kinds and arrangements of their teeth: all rodents have a single pair of upper, and a single pair of lower incisors that are separated, from several pairs of chewing teeth, by a large gap (diastema). The chewing teeth of typical mice consist only of molars, while squirrels and their allies, jumping mice, and cavylike rodents have both molars and premolars. Rodent incisors grow continuously from birth to death, and have chisel-like cutting edges:

Pocket gophers (Geomyidae)

  • Llano pocket gopher (Geomys texensis): subterranean; common in west-central part of Central Texas; small, dark brown or sandy brown on back, paler sides, white underparts; prefers deep sandy loam, gravel, or sand in Texas Hill Country; breeds in spring and early summer.

Pocket mice & kangaroo rats (Heteromyidae)

  • Hispid pocket mouse (Chaetodipus hispidus): terrestrial, throughout Central Texas; head and body 3.75 inches; large and colorful, with brown back, grizzled with orange and black; a broad orange lateral line on sides; white belly, broad orange ring around eye, bicolor tail is short and not tufted; breeds year-round; prefers grassy areas in plains and deserts, usually on sandy soils.
  • Merriam’s pocket mouse (Perognathus merriami): terrestrial, throughout Central Texas; head and body 2.25 in, tail 1.75 in.; breeds Mar-Dec; found on sand, gravel, and hard-packed soils.
  • Silky pocket mouse (Perognathus flavus): terrestrial, throughout Central Texas; head and body 2.25 in.; tail 1.75 in., shorter than other pocket mice; very small; grizzled orange-brown back, with pale orange lateral line, and white belly; sifts through sand for seeds, climbs stalks to harvest green seeds; breeds Mar-Oct; prefers sandy soils, rocky areas, and clays.

Mice & rats (Muridae)

  • Black Rat (Rattus rattus): arboreal, terrestrial, and opportunistically subterranean throughout Central Texas; head and body 5-7 in., tail 3-4 in.; scraggly black to light brown fur with lighter undersides; nocturnal, congregating around warehouses, residential buildings, and similar human settlements; prefer in urban settings to live in palm and pines; nests are ball-shaped and are made of shredded sticks, leaves, vegetation, and cloth; will build nests in abundant leaf litter and thick ground cover and under some circumstances will burrow into the ground; generalist omnivores, adapt to food supplies available locally; excellent vectors for disease transmission due to an ability to carry bacteria and viruses in their blood streams; particularly known to carry Streptococcus pneumoniae, Corynebecterium kutsheri, Bacillus piliformis, Pasteurella pneumotropica, and Streptobacillus moniliformis; preyed on by owls, cats, foxes, and coyotes.
  • Brown Rat (Rattus norvegicus): subterranean, terrestrial, and arboreal throughout Central Texas: head and body 8-10 in., tail 7-10 in.; brown or dark gray back with light gray underparts; nocturnal, excellent swimmer and burrower, often excavating extensive burrow systems; true omnivores, though cereals form substantial part of diet; breed throughout the year, females able to produce 5 litters annually; gestation period is 21 days, pups become sexually mature in five weeks, permitting populations to grow by a factor of 10 in 15 weeks; live in large, hierarchical groups in burrows or subsurface places such as sewers and cellars; generally begin new burrows adjacent to an object or structure, as this provides a roof for the set ion of the burrow nearest to the ground’s surface; burrows develop to include multiple levels of tunnels as well as a secondary entrance; burrows are used to escape perceived threats; carry a number of pathogens and parasites.
  • Deer Mouse (Peromyscus maniculatus): terrestrial, arboreal, and subterranean, throughout Central Texas; head and body 3.5 in., tail 2.25 in.; so closely related to the white-footed mouse (Peromyscus leucopus) that the two are best distinguished via RBC agglutination tests or karyotype techniques, though, physically, the deer mouse is distinguishable by its long, multicolored tail; 66 subspecies are recognized, all are tiny and plentiful throughout their range; nocturnal, foraging by night, spending day in trees or burrows, the latter having nests of plant matter; reproduce throughout the year, esp. Mar-Oct, var. based on food availability; preyed on by snakes, owls, skunks, foxes, and domestic cats.
  • Eastern woodrat (Neotoma floridana): terrestrial, semi-arboreal, and subterranean pack rat, on eastern edge of Central Texas; head and body 9 in., tail 6.25 in., moderately haired; back gray brown, dark brown, or sandy brown; sides washed with buff; belly grayish white or cream white; ears large; eats leaves, fruit, berries, fungi, nuts, and seeds; in east Texas uses underground burrows; breeds year round; common, widespread, and able to thrive in a wide variety of habitats.
  • Fulvous harvest mouse (Reithrodontomys fulvescens): arboreal and terrestrial, on northern, eastern, and southern edges of Central Texas; head and body 2.75 in., with long tail; back rusty brown peppered with black, sides orange, belly white or buff; breeds in spring and fall; constructs baseball sized nests of shredded plant material in vegetation.
  • Hispid cotton rat (Sigmodon hispidus): terrestrial and subterranean throughout Texas; head and body 6 in., tail 4 in.; upper parts grizzled dark brown and buff, belly grayish white; mainly crepuscular but active day or night; eats grass and other plants, insects, and fungi; makes nests in thick grass clumps or short underground burrows.
  • House mouse (Mus musculus): terrestrial, throughout Central Texas; head and body 3-3.9 in., tail 2-3.9 in.; fur light to dark brown; adults are good jumpers, climbers, and swimmers, are crepuscular or nocturnal, sleep 12 or more hours a day, and nest in cryptic places near food sources; naturally omnivorous, but preferentially feeds on plant matter; known to be capable of transmitting a few human diseases, including Lymphocytic choriomeningitis, but such infections are  not commonly reported and, when diagnosed, are generally mild; mice often contaminate food and damage food packaging; mice tend not to be as infested with fleas as rats, and thus are not effective vectors of plague.
  • Northern pygmy mouse (Baiomys taylori): terrestrial and subterranean, throughout Central Texas; head and body 2.5 in., tail 1.75 in.; dark gray-brown back, gray sides, grayish white belly; small eyes, medium ears, tail short and nearly naked; mainly nocturnal but sometimes diurnal; eats seeds, fruit, green vegetation; nest is ball-shaped with one or two openings, and is situated under logs, in vegetation, and in small burrows.
  • Plains harvest mouse (Reithrodontomys montanus): terrestrial, throughout Central Texas; head and body 2.7 in., tail 2.25 in.; feeds on weed flowers and seeds, and on grasshoppers and other invertebrates; nest is ball shaped constructed on or just above the ground; breeds year round; prefers open countryside with short grasses.
  • Southern plains woodrat (Neotoma micropus): terrestrial, in western half of Central Texas; head and body 8.5 in., tail 6 in.; large, with back and sides steely gray or blue-gray, white belly; eats cactus leaves and fruit, mesquite beans, acorns, and plant matter; makes a house under prickly pear cactus, with 2-5 entrances, and likely uses the house for life.
  • Texas mouse (Peromyscus attwateri): terrestrial and semi-arboreal throughout Central Texas; 3.75 in. head and body, 4 in. tail; eats seeds, other plant materials, and insects.
  • White-ankled mouse (Peromyscus pectoralis): terrestrial, throughout Central Texas; head and body 3.75 in., tail 3.75 in.; gray-brown upper parts, brown sides with narrow orange lateral line, white belly; often found on rock ledges and in leaf litter; eats juniper berries, acorns, hackberries, seeds, and invertebrates; breeds year round.
  • White-footed mouse (Peromyscus leucopus): terrestrial, semi-subterranean, and semi-arboreal, throughout central Texas; head and body 3.5 in., tail 3 in.; dark brown upper back, sides orange-brown, white belly; eats seeds, nuts, fruit, invertebrates, and vegetable matter; makes ball-shaped nests in logs, standing trees, abandoned burrows, bird nests, and inside man-made structures; breeds mainly in spring.
  • Woodland vole (Microtus pinetorum); subterranean, throughout Central Texas; head and body 4 in., tail 0.75 in.; reddish brown back, orange-brown sides, gray belly; eyes and ears small; eats roots throughout the year, grass stems in summer, fruit and seeds in the fall, bark in winter; breeds year round; favors sandy soil.

Squirrels (Sciuridae)

  • Black-tailed prairie dog (Cynomys ludovicianus): subterranean; along the western edge of Central Texas; though capable of invading yards and landscapes, it is unlikely to do so.
  • Eastern gray squirrel (Sciurus carolinensis): arboreal and terrestrial; eastern half of Central Texas; uppermost parts gray with yellow-brown cast on upper back and head; white or pale orange eye-ring; ears gray to rusty brown, sometimes white with slight tuft in winter; white belly; mainly arboreal but spends much time on ground; nest made of twigs, leaves, and plant material, in hollow trees or inside hollow trees; each squirrel uses more than one nest; breeds twice a year in Jan-Feb and June-July; favors hardwood forests.
  • Fox squirrel (Sciurus niger): arboreal and terrestrial; throughout Central Texas; variable in color but most commonly grizzled yellow-brown above, with pale orange to rusty brown belly, cheeks, eye-ring and feet, and tail edged in orange-brown; larger than eastern gray squirrel where range overlaps; travels and rests in trees, but feeds extensively on ground; eats nuts, acorns, seeds, fungi, and fruit; makes leaf nests on branches, in hollow trees, or in voids of man-made structures; mates Jan-Feb and May-June; prefers open stands of deciduous and evergreen woodlands, shunning woods with dense undergrowth or closed canopies.
  • Mexican ground squirrel (Ictidomys mexicanus): subterranean and terrestrial; throughout Central Texas; feeds on mesquite leaves and beans, grass and herb seeds, insects, carrion, and small vertebrates. It makes burrows that have multiple entrances, and willingly uses the burrows of pocket gophers. It prefers areas with sandy soils.
  • Rock squirrel (Otospermophilus variegates): arboreal, terrestrial;  throughout Central Texas; in Texas most commonly found with blackish head and shoulders, dark brown or cream forelegs, but can be entirely black with a pale eye-ring and yellowish belly; mostly seen on the ground but capable of climbing well and sometimes nests in trees; eats fruit, seeds, plant matter, roots, cacti, and invertebrates; prefers rocky canyons, cliffs, and hillsides in arid areas.
  • Thirteen-lined ground squirrel (Ictidomys tridecemlineatus): subterranean and terrestrial; along the eastern edge of Central Texas; is the “gopher” most people notice along roadsides, on lawns, and on golf courses. It eats seeds of grasses and herbs, but will also consume small insects and vertebrates. Though they will form colonies when conditions permit, adults are not social and defend only the areas around their nest burrows. Deeper nest burrows are built near shallow escape burrows. They prefer short grass meadows and prairies, and avoid wet, low-lying areas.


Appendix C: References to Scientific Literature


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One comment on “Stopping an invasion of Raccoons, Skunks, Opossums, Rodents, Feral Cats, and a Fox, at a home in Northwest Austin…

  1. Anthony Ball Mar 17,2015 12:18 pm

    Awesome insights on steps homeowners can take to prevent animal invasions at their home. As a pest control professional, I’ve also learned that rodent exclusion techniques are work best for long term success in keeping the critters out. Here is a great infographic from the NPMA about the growing rodent problem in America:

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