On Thursday, 9 October 2011, Amy G. called and said:
“Hey, Jerry… We have some new friends — actually a few bats — in our garage. They are pooping bat guano all over our cars, and we don’t quite know what to do about them. Do you have any ideas? We’re at the end of our rope here.”
Amy and her husband are good friends. I’ve known Amy, and practically everyone in her extended family, since she was a young lass growing up in Georgetown, Texas, way back in the mid-1980’s. Now she’s the mother of a tribe of beautiful children. Not only are she and her executive husband busy with the chores of raising a family, they also run a thriving corporation.
Though bat biologists quickly point out that these flying mammals are extremely beneficial to humans, they acknowledge that they also pose a risk of rabies exposure and carry other diseases — notably the fungal respiratory infection histoplasmosis — and, for those reasons alone, it is generally advisable for humans and bats to maintain a respectable distance between one another.
Children tend to be most at risk of exposure to the diseases carried by bats.
Amy’s news about the bats at her home was not a big surprise. The unusually protracted drought of 2011 — in Texas, Oklahoma, New Mexico, and Arkansas — led most species of wildlife to behave in unexpected ways. I’ve written about the drought-related behavior of snakes and rodents, and the juvenile western cottonmouth snakes that have troubled one family in Manvel, Texas, in previous postings. Amy’s situation demonstrates how the drought affects the bats of Texas when their normal food supplies of mosquitoes and other flying insects, within their natural foraging zones, have diminished to almost zero.
Texas is home to more kinds of bats than anywhere else in North America, with 32 known species found within the state. Some, like the 1.5 million Mexican free-tailed bats (Tadarida brasiliensis), in the Molossidae family, famously occupy the grottoes beneath the Congress Avenue bridge in downtown Austin, forming one of the largest maternity colonies in the southwestern U.S. A similar, though smaller (estimated in excess of 1 million), maternity colony occupies the grottoes beneath the McNeil Road/I-35 Overpass bridge in southern Round Rock.
Those two colonies, alone, reputedly consume from 36,000 to 50,000 pounds of flying insects every night. That makes them incredibly efficient at keeping local populations of flying insects — including disease vectors such as mosquitoes and flies — in check. Likewise, practically all the other species of bats found here and throughout North America are also almost exclusively insectivorous, catching huge numbers of flying insects while foraging at night, on the wing. The aggregate demand for such insects, by all these bats, is very high. When bats are unable to satisfy that demand, they are forced to modify their behavior. For some, if not most of them, that means packing up and moving to new habitat.
The bats found at Amy’s home are members of the largest bat family found in the world, the Vespertilionidae. Thanks to the efforts of Kate Rugroden, director of Bat World Mid-Cities in Arlington, TX, we at BugsInTheNews are becoming more familiar with these and the other families and species of bats found in Texas and North America.
FOOD FOR THOUGHT: Bats, skunks, armadillos, raccoons, opossums, squirrels, and other mammals sometimes take up residence in the attics, basements, walls, and other portions of residential and commercial structures. Since such locations are not appropriate nesting spots for wild animals, and exposes people to a number of unusual diseases, it is imperative that they be removed quickly, safely, and efficiently. Most home or business owners are not equipped to properly perform a mammal exclusion project at their homes or businesses. You may believe you are an exception to this rule, and it may be true. If, however, you mistakenly believe mammal exclusion is a trivial job, and you don’t have the time or interest needed to (1) study all the legal/technical issues involved, (2) tackle all the mechanical habitat modifications, (3) obtain and properly use the protective gear needed to avoid injury from or contamination by the animal and its associated disease-causing organisms, (4) inspect for, find, and then seal all the ingress/egress ports in your home’s or business’s exterior, (5) clean up, disinfect, and remove the contaminants left behind by the animal, and (6) do all this within a reasonable time, it is wise to face the fact that you are no exception. What you need is a wildlife specialist with expertise in wild animal biology, removal, disinfecting and control. To find a qualified wildlife specialist in your local area (anywhere in North America), call Jerry RIGHT NOW at 512-331-1111.
We have a lot to learn. Carefully studying each of the 32 species of bats found in Texas is a vast undertaking, and we’re grateful that Kate and others like her are so willing to help. These people have a passionate concern that information on bats, posted on the Internet, is accurate, unbiased, and informative. With their help, what is posted here will meet all three of these descriptors, and two more — that such information is as complete and presented in a form that is as easily understood as possible — as well. As we learn from Kate and her fellow bat rescue specialists, we will be posting more details. But we want to get our information right, and that takes time, so bear with us.
Satellite Colonies of Bats in Texas:
When, seemingly out of nowhere, a colony of bats suddenly takes up residence at a place where they had not been observed before, the most obvious source is another, not-too-distant colony of the same species that became overcrowded. Sometimes, however, the source can be a relatively distant colony whose members were unable to find enough food at the old colony’s location and were forced, by hunger, to find a new location from which to launch their nighttime foraging activities.
In our 30-plus years of watching the comings and goings of bats in central Texas, we’ve rarely seen as many satellite colonies of bats, in so many different locations, as in the summer of 2011. We suspect these are somehow associated with the natural habitat adjustments brought on by the ensuing drought, which by now — in early 2012 — is entering its third straight year.
Bat habitat adjustments may occur for a variety of reasons, but one particular reason is probably more common than the rest. Established maternity colonies often become overcrowded from the newly fledged pups produced in the current year. When this happens, colony members that are in the way — i.e., those males not directly involved in caring for the pups — are pushed out and forced to find a new home. These males will usually find cryptic roosts nearby. Typically such roosts, which are situated beneath smaller bridges, and inside attics and eaves of homes and other buildings where access holes to such places are not properly sealed, are not visible during the daytime.
In 2011 (not an ordinary year), a general lack of flying insects, rather than the overcrowding of maternity colonies, may be the most common cause behind the bat habitat adjustments we’ve observed. These satellite groupings are distinct from the normal maternity colony overflows. They are not located in close proximity to long-established maternity roosts, and often contain female and male bats in roughly equal numbers. This suggests that they may result from an expanded foraging territory, brought on by the lack of flying insects in the territories where they’ve foraged in the past.
After a long night of long-distance foraging — some bats find it difficult to return to their old haunts before daybreak. That’s a problem, because a bat found flying in the daytime has a huge target on its back. Such bats quickly become food for owls, hawks, falcons, and a host of other feathered predators. As a result, bats that are still a long way from home when the sun begins to brighten the eastern horizon wisely seek out a place to roost nearby. Protection from predators improves with numbers, so such bats tend to congregate together. And, voila! a satellite grouping is born that, in many cases, becomes a semi-permanent roost for that particular year.
The dynamics of the reduced insect populations we’ve observed in 2011 increase the likelihood that isolated satellite populations, as described above, will — themselves — fall victim to overcrowding. This happens, not because of maternity-mediated population increases, but because of a paucity of cryptic grottoes at the satellite locations. These tend to be located further away from urban settings, in places where large cryptic grottoes are less plentiful. As a result, when a large number of bats attempts to roost in the same spot, some are often forced to hang out in shady spots on the exterior of the roost, where they are visible throughout the day.
It is easy to presume, when one sees isolated groupings of bats in the daytime, that “what you see is what you have,” but that’s usually not the case. A closer inspection of the roosting site usually reveals the presence of cryptic grottoes nearby that are full of bats, to the point of overflowing. Such was the case at Amy’s home. In her case, the bats in the garage appeared to be overflows from a larger bat population in the large cedar pergola in her back yard, where it was attached to the home. That pergola was better constructed than most, with a hollow subfloor ceiling in which lots of bats could congregate. Once that space was filled to the brim, the overflow had to move elsewhere, and the recessed light fixtures of the garage turned out to be an excellent place — from the bat’s perspective — in which to do just that.
Flying insects in many, but not all, drought-affected areas are severely depressed. Notable exceptions are captive bodies of water — livestock tanks fed by natural springs, and inland lakes with lagoons and estuaries along their boundaries — where mosquitoes and chironomid midges remain bountiful. Practically everywhere, except at such places, a significant reduction in flying insects was observed throughout 2011. Our surveys of the estuaries around Lake Conroe and Lake Houston indicated that the flying insect fauna normally found around those bodies of water were at least as robust as, and in some cases even more plentiful than, they had been in the previous few years.
In the coming days, weeks, and months we’ll be publishing detailed information on here about Amy’s bats and the steps that were taken to exclude them from her garage and pergola. But first, we’ll share the consequences that followed being bitten by a bat while removing one of these furry little creatures from a residential light fixture.
Bat Bites & Rabies:
Bats are notorious carriers of the rabies virus. This can be a controversial subject, with certain bat advocacy groups arguing that the rate of rabies within bat populations is way overblown, and leads to irrational fears and indiscriminate killing and mistreatment of these animals. The Centers for Disease Control (CDC), without addressing animal treatment concerns directly, argues the contrary view that, in some locales, bats pose the greatest risk of rabies exposure of any of the region’s wild animal populations. Worse, says CDC, the fact that a bite from a rabid bat only rarely produces a visible wound leads adults to think such bites are unimportant when — in fact — they pose as serious a risk as a bite that draws blood. Worse still, says the CDC, parents of small children usually presume that bats, when found in nurseries where their children have been sleeping, did not bite those children simply because no evidence of bite marks can be seen. A number of invariably fatal rabies cases in small children, following sightings of bats in their sleeping areas, have led CDC researchers to recommend immediate rabies vaccinations whenever such scenarios are observed.
Depending on the source, reports indicate that anywhere from 0.5% to over 30% of the bats in a given population are infected with rabies at any one time. Even at the low end of this range, the chance of being bitten by a rabid bat is 1 in 200, which isn’t very good odds; at the upper end, the chances the bat that bit you is rabid rises to 1 in 3. Thus, a bite from one of these creatures — even when the bite wound is not visible (bat bites rarely result in a visible wound, owing to their tiny teeth, as shown in the photo at the head of this article) — should always be followed up with a round of post-exposure rabies immunizations.
As a wildlife specialist, experienced in the biology of most of the mammals found in North America, I know all the personal risks that attend working with wild animals. Some day, I figured, a bite from one of the animals that got too close to me would necessitate a trip to the emergency room. It finally happened, after 31 years of not one previous bite of medical consequence, when a bat latched onto the unprotected wrist of my gloved left hand. I then used my right hand, ungloved to enable it to easily open and close an animal carrier I was placing the bats into, to remove the bat from my left wrist and — in the process — my left wrist and right thumb got bitten, and the offending bat got loose and flew away before I could secure it in the carrier.
Such a mistake is easy to make. But mistakes teach great lessons to those willing to learn. Perhaps you can learn some of those lessons by reading about mine here.
These bat bites resulted in four visits to the emergency room. Rabies vaccinations in this part of Texas are only performed by hospital emergency rooms that have pharmacies capable of carrying, storing, and preparing injectable quantities of rabies vaccine for their patients. Doctors, in private practice separate from hospitals, in minor emergency centers, and with medical clinics not in a hospital itself, are not equipped to handle such vaccines. This results from the fact that each injection must be prepared individually, based on the weight of the person undergoing vaccination.
Rabies vaccinations are conducted in a series of four, on each of four separate days. The first date of vaccination is referred to as Day 0. On this visit, human rabies immunoglobin (in my case, Talecris HyperRAB S. D., or HRIG; see Manning, 2008), was injected. About half of the HRIG dose went directly into the fleshy areas immediately surrounding the bat bites themselves, and the rest was injected at a site distal from the bite wounds; in my case, the left buttock. Since I’d not had a rabies vaccination before, the HRIG injection was required by CDC protocols. It provides a passive antibody that attacks the rabies virus immediately.
Afterward — still on Day 0 — I was injected with human rabies diploid cell vaccine, or HDCV (Manning, 3008), intradermally, in my choice of muscle. I chose the deltoid of the left shoulder. This is an active vaccine that stimulates the immune system to manufacture rabies antibody to lead a prolonged attack on any rabies virus the bat bites may have introduced. The HDCV vaccination, developed in 1967, is more expensive than the older nerve-cell derived vaccines that require multiple injections into the stomach muscle, but is more easily — and less painfully — administered.
Three days later — on Day 3 — I returned to the emergency room for a second HDCV injection. This injection was repeated twice more, on Days 7 and 14.
The total cost of these emergency room visits came to $11,431.00. The first visit (Day 0) cost $8,832.00 (77% of the total). The major portion ($7,390.00, or 83%) represented the HRIG passive antibody injections. The HDCV injection, on that date and on each of the subsequent visits, came to $502.00 each. The upside of this picture is that the vaccine provides nominal protection against future rabies exposures for two years, and after that — if tests show the degree of protection has dropped below the recommended threshold — a booster shot will raise the level of protection back to the recommended level. Note, however, that even with the nominal protection provided by the rabies vaccine, a booster shot is usually given any time a future exposure occurs.
Lesson: don’t get bitten by a bat. The time you will spend dealing with the rabies vaccinations is enough disincentive by itself, but when you add up the monetary expenses too, well… Don’t get bitten by a bat.
Bats and Bat-Bite Avoidance:
So, you ask, what can you do to avoid contact with bats, and — in particular — to keep from getting bitten by a bat? One important way is to simply avoid contact with bats that you see in your environment. Two basic situations are usually encountered. First are temporary outdoor roosts, with the bats roosting in the open, where they can be seen by someone walking around their home outside. The second situation involves cryptic roosts, hidden from view, inside an attic, eave, or other man-made enclosure.
Bats in Temporary Outdoor Roosts:
If you find a bat attached to a portion of your home (they are often found in the corners of doorways, under eaves, under porches, and — as in Amy’s case — in the recessed light fixtures in garages and pergolas), don’t go near that location during the daytime. When night falls, the bat will almost certainly fly off to forage for insects, and while it is gone you can spray the temporary roost where it was last seen with a non-toxic, non-pesticidal, non-repellent habitat modifying cleansing agent that will dissolve and obliterate the pheromones and other odors left there by the bat during its previous respite.
Almost any strong-smelling natural-plant-oil-based product labeled strictly as a cleansing agent will do the trick, as long as it has enough residual cleansing action to last two or more days. Keep in mind that the purpose of using these products is strictly to cleanse the roost area of pheromones and other roost odors, making the roost attractant-neutral, so that the bats will not find the roost enticing when they return before day-break. On discovering that the roost odors that attracted them the previous day are no longer present, most if all the bats will pass the now-cleansed roost by and search out a new place to roost, usually a significant distance away (though, if a suitable location nearby is found, the bats may simply move to that location).
Using anything, including non-toxic sprays of any kind, to actively dislodge or influence the bats presently in a roost is not advised. Furthermore, toxic sprays labeled as pesticides or repellents may harm or kill the bats and their pups. As a result — in general, regardless of the endangered or protected status of the species, but particularly if the bat species involved is listed as endangered — using such products may constitute a criminal violation of state and/or federal law with severe penalties.
Bats in Cryptic Roosts:
If the roost is in a natural setting, such as a hollow tree, a cave, or the underside of a cliff, and does not directly endanger the human inhabitants of the property, the roost should be recognized as part of their natural habitat. Such roosts should not be disturbed so long as the bats are using that roost. It is advisable to consult with a wildlife specialist with expertise in bat biology to determine the species of bat involved. If the bats happen to be an endangered species, any attempt to disturb such roosts may constitute a criminal violation of state and/or federal law, which can result in severe penalties.
If the roost is partially hidden from view, the possibility exists that more than one bat is roosting there, and even that one or more members of a maternity colony may be present — though out of sight — during the daytime hours. If so, calling in a wildlife specialist with expertise in bat biology is imperative, as using any kind of cleansing agents, in cryptic bat habitats, may bring the agent into contact with nursing females and their pups, resulting in pup abandonment.
One-way doors, constructed, installed, and maintained by experienced wildlife specialists with expertise in bat biology, constitute the primary means of excluding bats from cryptic roosts in residential and commercial structures during the time period when the bats are actively using the roosts. For some species of bats, using mechanical exclusionary techniques to control access to a cryptic roost can result in de facto maternal abandonment, if — for that species — it is not unusual for the pups to not be constantly attached to the mother. Unattached pups are often too young or too weak to proceed through one-way doors on their own power, and for this reason, such exclusionary devices should not be used during the early portion of the maternity season.
Cleansing Roosts in Cryptic Areas not Conducive to Exclusionary Techniques:
Some locales are not conducive to bat exclusionary techniques. Examples are expansive attics in barns, sheds, commercial structures, and the like, which are easily accessible via a large number of alternative ingress/egress ports that cannot be easily, economically, or practically fitted with one-way doors. In such cases, the roosts can be cleansed to make them attractant-neutral, prompting the bats to go in search, elsewhere, for a new roost.
Bats are extremely sensitive to the smells around them, especially when roosting. When choosing a new roost these animals will first seek out a place where existing bat pheromones and other odors associated with bat roosts already exist. Failing to find such places, they opt instead for locations where the intrinsic odor is easily transformed to that of a well-used roost, i.e., where they are able to contribute fresh odors that will attract additional bats of their species over time.
Most bats roost only in places that they find attractive and nurturing; unattractive, non-nurturing locales, or locales with strong plant odors that are not compatible with their natural pheromones, are passed by. This occurs, not because such places are repellent, but simply because the bats have other options that, by contrast, offer the positive degree of attraction and nurturance that they favor.
Strong smelling, long lasting plant oil sprays applied to unwanted bat roosts are not injurious to the bats that roost there. However, they may cause the bats to scatter if applied while the bats are present. For this reason, they should only be applied when the bats are absent (that is, during the nighttime hours when the bats are away).
Before cleansing a cryptic roost, the entire roost must be carefully mapped — during the daytime hours when the bats are present — to thoroughly document exactly where they are roosting. Later, when the bats are absent, the roost may be cleansed with a strong-smelling, non-toxic, non-pesticidal, non-repellent plant oil spray. It is important that this be done only after a thorough inspection is carried out to insure that no stragglers are present.
It is advisable to consult with a wildlife specialist with expertise in bat biology, and to hire that specialist to map, inspect, and cleanse any cryptic bat roost for you, rather than to attempt such work as a do-it-yourself project. An experienced wildlife specialist will wait until well after dark to cleanse the bat roost, as that is when the bats are out of the roost foraging for insects. Later, when the bats return to the roost, most if not all will choose another place to spend the night. If a few hangers-on persist in gathering there, the wildlife specialist will wait again for night fall and re-apply the cleansing agent. After one or two additional applications, the bats will usually cease using that roost for the season, though it may be necessary to cleanse such roosts several times a year.
What the Future may Hold:
The extensive satellite bat colonies observed in 2011 are likely to be around in 2012 as well. The present drought is projected to continue throughout the present decade, mirroring in many ways the protracted drought of the 1950’s. This means that more humans will be finding bats around their homes in the future, and that increases the likelihood that experiences like mine will multiply. You need to know the best way to deal with the bats you find, and you especially need to know what to do if you, someone you know, or one of your children are bitten by one of these furry flying creatures.
Our plan is to share that information right here, the moment all the other projects presently underway can be put on hold long enough to key the details into this web page. Considering how important that information is for your safety and peace of mind, we’re taking strenuous steps to do that as quickly as possible.
- Phylum: Chordata — animals with a having, for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail.
- Class: Mammalia — air-breathing vertebrates with hair, three middle ear bones, and mammary glands that function in mothers with young.
- Order: Chiropoda — flying mammals (all of which are known as bats) with webbed forelimbs developed as wings that make them capable of true and sustained flight. Between 1,240 and 1,300 species of bats (95% of which are not represented in the U. S.) are recognized worldwide, in two suborders, only one of which (Microchiroptera) is found in the U.S.
- Family: Four families of bats, comprised of forty-seven distinct species, are found in the United States and Canada, the latter with twenty of the total, all of which are also found in the U. S. (Harvey et al., 2011). All four families of bats are also found in Texas, though but thirty-two of their species are found there (Schmidly & Davis, 2012) [but note that some authorities disagree on this number, and on the list of species that is correct; note further that four additional species of bats, all in the Phyllostromidae family, are on rare occasions found in the U.S. but, because their presence is sporadic and unintended, are classified as “accidental” (Harvey et al., 2011)]. Those bats known to be found in Texas are listed below (in a combined list taken from Harvey et al., 2011, and Schmidly & Davis, 2012):
- I. Family Mormoopidae (leaf-chinned bats), represented in Texas by one genus and one species;
- II. Family Phyllostomidae (leaf-nosed bats), represented in Texas by three genera and three species (one of which — the hairy vampire, Diphylla ecaudata — feeds on blood, mostly that of birds; this species, though only occasionally entering Texas from Mexico in the past, is now believed to be a regular invader of the state, owing to the unusually warm climate of the past few years… some authorities expect it to become endemic in Texas if current trends continue);
- III. Family Molossidae (free-tailed bats), represented in Texas by three genera and four species, including the most famous of Texas bats, the Brazilian free-tailed bats that roost under the Congress Avenue Bridge in downtown Austin, Texas; and
- IV. Family Vespertilionidae (vespertilionid or vesper bats): known as vesper bats, or common bats, this is the largest and best-known of the bat families found in Texas, and is the family from which Amy’s bats (the subjects of this article) hail. The name is derived from the Latin word vespertinus = of the evening. Most are insectivorous, but some prey on fish or on small birds as well. Though relying on echolocation, their noses are not specially adapted to detecting ultrasound echoes as in other families, and they emit their ultrasound chirps in a forceful manner, as though shouting through their open mouths. The ears of some are enlarged to compensate for the lower efficiency that accompanies this manner of ultrasound production. Roost size ranges from solitary, to huge colonies. Most roost in caves, others in hollow trees, natural crevices in rocky cliffs, in the burrows of animals, and in manmade cavities in urban and suburban areas. Nine genera and 24 (or 25, according to some authorities) species of vesper bats are known to be found in Texas:
- Genus Myotis. Nine species are found in Texas:
- (1). Southeastern Myotis, Myotis austroriparius;
- (2). California Myotis, Myotis californicus;
- (3). Western Small-footed Myotis, Myotis ciliolabrum;
- (4). Little Brown Myotis, Myotis lucifugus;
- (5). Northern Myotis, Myotis septentrionalis;
- (6). Fringed Myotis, Myotis thysanodes;
- (7). Cave Myotis, Myotis velifer;
- (8). Long-legged Myotis, Myotis volans; and
- (9). Yuma Myotis, Myotis yumanensis.
- Genus Lasionycteris. One species is found in Texas:
- (1). Silver-haired Bat, Lasionycteris noctivagans
- Genus: Pipistrellus. Two species are found in Texas:
- (1). Western Pipistrelle, Pipistrellus hesperus; and
- (2). Eastern Pipistrelle, Pipistrellus subflavus.
- Genus Eptesicus: One species is found in Texas:
- (1). Big Brown Bat, Eptesicus fuscus.
- Genus Lasiurus. Six (or seven, according to some authorities) species are found in Texas:
- (1) Western Red Bat, Lasiurus blossevillii;
- (2) Eastern Red Bat, Lasiurus borealis;
- (3) Hoary Bat, Lasiurus cinereus;
- (4) Southern Yellow Bat, Lasiurus ega;
- (5) Northern Yellow Bat, Lasiurus intermedius;
- (6) Seminole Bat, Lasiurus seminolus; and (according to some authorities)
- (7) Western Yellow Bat, Lasiurus xanthinus.
- Genus Nycticeius. One species is found in Texas:
- (1) Evening Bat, Nycticeius humeralis.
- Genus Euderma. One species is found in Texas:
- (1) Spotted Bat, Euderma maculatum.
- Genus Plecotus (Corynorhinus). Two species are found in Texas:
- (1) Rafinesque’s Big-eared Bat, Plecotus (Corynorhinus) rafinesquii;
- (2) Townsend’s Big-eared Bat, Plecotus (Corynorhinus) townsendii.
- Genus Antrozous. One species is found in Texas:
- (1) Pallid Bat, Antrozous pallidus.
- Genus Myotis. Nine species are found in Texas:
Anatomy: in process
Behavior: in process
Common Names: Vesper bat.
Distinguishing Characteristics: in process
Distribution: in process
Physiology: in process
Mythology: in process
Similar Families: in process
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