Natural Predators of the Puss Caterpillar 9

For years, I’ve observed the curious fact that puss caterpillars seem to be most successfully exterminated by their own natural predators. Their infestations are models of an effective natural-predator sequence: If humans do nothing, they flourish for a short time and die, evidently because something in their natural environment utterly destroys them. Yet, if commercial pesticides are applied, the caterpillars tend to survive, usually in enough numbers to produce new infestations, often worse than before. Ergo, commercial pesticides–including the biological, “green” ones–appear to produce exactly the opposite result intended. When this happens (and it happens with regularity in nature) the wise observer looks for evidence that the pesticides are killing the target pest’s natural predators more effectively than they kill the target. Once I did that, the evidence at hand was overwhelming.

Before going further, perhaps a few words should be said concerning my feelings about commercial pesticides. I’m not opposed to their use. In fact, as a pest manager who has used pesticides of various kinds for decades, I’d have a natural bias in their favor if they worked as advertised to control this particular pest.

Here’s what I know for sure: In some cases, commercial pesticides offer the best approach to resolving pest issues; in other cases they are less than effective; and in a few situations–including the one under evaluation here–they actually create more problems than they solve. Pesticides must be evaluated alongside all the other alternatives available, and once the evaluation is complete–and all the factors have been considered–the best solution is the one that works the best with the fewest complications and side effects, at the lowest cost. I add the last item, “at the lowest cost,” not because I am miserly, but because there seems to be a natural law that the cheapest solution is often the best one. At my age (I’m now on the other side of 70) that law has been tested over and over again in my life, and it has been found true many more times than it has been found wanting.

Identity Unknown… Over time, more examples of this natural-predator sequence came to my attention. Yet, though much is known about the enemies of ordinary moth and butterfly larvae, those affecting the puss caterpillar have not been widely described, at least in recent publications. These caterpillars bristle with stinging spines that inflict pain of gargantuan proportions. Trained entomologists at major universities avoid working with them in the lab, out of concern for the effects of their stings (though I can attest that, by implementing a few simple precautions, one can safely work with hundreds of these caterpillars, in a laboratory environment, without suffering a single sting). Avoiding a sting is key, since they may send you to doctor’s waiting room chair if the injury is severe enough. It stands to reason, then, that their natural predators would have to employ unusual methods to get past those spines and prey on them. These same predators would also have to be rather ubiquitous, because no matter where puss caterpillars show up, their predators soon steal the show. And, they would have to be unusually susceptible to commercial pesticides, more susceptible, in fact, than puss caterpillars. But, as far as I knew, nobody had any idea what those natural predators were (it happens, however, that numerous surveys of the parasites of these caterpillars have been conducted in the past; the results of those surveys surface in the form of obscure references, in scientific media, to the species of caterpillars that various parasitoids are known to afflict).

A Call to Action: In October 2009 I received a call from a woman who was employed at a construction company in Temple, Texas. She’d just been stung by a puss caterpillar and wanted extermination advice. I replied, as usual, “Don’t spray them; their natural predators will do the job for you.” She answered, “And what would those be, sir?” I explained that we didn’t know, and she replied “Well, why not?”

How embarrassing! Despite having studied these caterpillars for over eight years, I couldn’t tell her what Mother Nature used so efficiently to wipe them out. But after receiving thousands of such calls over the years, I’ve developed a kind of educated callous. Becoming comfortable in my ignorance, I accepted how little I know about nature and–unlike the child of my youth–no longer believed I needed to find answers to every conundrum that pops up. Oh, I know, one should never be comfortable in one’s ignorance, but the human condition seems bent on making me, and perhaps all of us, so.

The Final Straw… A few days later this same woman sent me an email to report another sting. Then, a few days after that, she called to say that she had received a third one that was so painful it had made her physically sick. She had just vomited, and sounded genuinely upset and afraid. She believed she had to demand that the owner of the building have a pest control company come out to spray the puss caterpillars into oblivion. I reiterated to her how important it was not to do such a thing, but my words seemed hollow, even to me, because I could not back them up with scientific fact. Suddenly, the beguiling comfort of ignorance evaporated. I suggested she talk her boss into giving her the afternoon off, and promised to do something to help. My version of “help” was, of course, to learn more about these caterpillars and their natural predators. That afternoon I drove to Temple, ready to work on answers to her questions.

At the site: The puss caterpillars were infesting a mature yaupon holly hedge along one side and bordering the front of the office building. Thousands of puss caterpillars were still there, munching away. Many of the caterpillars were ready to pupate, and had migrated to the walls of the structure, getting on the door, doorframe, and threshold. One was on the door handle, where the woman (now at home to recuperate) had received her last sting. Lest it be erroneously construed that she was unusually clumsy, her three stings were not the result of inattention on her part. The last sting, for example, was nigh unto unavoidable. She’d simply operated the lever to open the door, inadvertently contacting a caterpillar hidden behind the lever.

The building was 21 years old, and–according to the owner–had never, ever, been exterminated, inside or out. Only one other puss caterpillar infestation was known to have occurred in the past, and that was about 6 or 7 years ago.

Using a large collection bin, I removed 220 caterpillars, along with the small, leafy twigs they were munching on (see the photo above).  Several nearby grocery stores would, I knew, have the raw potatoes and ginger needed to make a dressing, if worse came to worse. One can never be overly careful…

Fortunately, however, I was careful enough not to come into direct contact with any of the caterpillars. Taking my time, and using heavy-duty tweezers and sharp wire cutters (to snip the twigs) to their full advantage, it was possible to avoid the painful results of slipping up, but such work is not the purview of those who are careless, in a hurry, or just plain unlucky. The collection work took a little more than an hour. During that hour I took pains to watch for the possible presence of wasps or other flying insects that might be attacking the caterpillars; none were observed physically attacking them, though I did notice a few fast-flying flies darting into and out of the shrubbery.  Once the collection work was done, the bin of puss caterpillar specimens was sealed, with its cargo safely inside, and immediately transported to my lab in Round Rock, about 50 miles from the original infestation site.

In the Laboratory:The collection of caterpillars was weighed, caterpillar by caterpillar, to the milligram level, then divided up and distributed into 15 plastic, vented rearing containers. The latter were then placed in a temperature-controlled environment. As the caterpillars depleted the foliage on the twigs, fresh yaupon holly–from a shrub located near the lab–was added as needed to keep them supplied with food.  These caterpillars depleted the original foliage brought from Temple within three days, whereupon the original yaupon leaves were entirely replaced with leaves from the local, uninfested shrub.

As each rearing container was examined and cleaned, the fecal pellets that had collected in them were poured into a separate, closed container. Microscopically (see the photo below), each pellet is shaped as a hollow sphere, open at one side. The feces collection container, when opened, gave off a relatively strong, yet unexpectedly pleasant, odor. I asked my wife if she would try to recognize the smell. The very idea made her nose wrinkle, but when I persisted and she reluctantly caught a whiff, her eyes widened in surprise. “Tea,” she mused, “it smells just like a freshly-opened tin of dried tea leaves.”

Caterpillar Scatology… Fecal pellets are known to be involved in the biology of various caterpillars in interesting ways. For example, Martha Weiss, an ecologist with Georgetown University, Washington D.C., discovered how and why skipper butterfly caterpillars–as Stanley Caveney, a biologist at the University of Western Ontario, Canada, first noted–explosively launch their fecal pellets, like tiny projectiles, a considerable distance from their foraging areas. They appear to do so, she observed, to thwart predation from certain parasitic wasps. The wasps, for their part, use the odor of the pellets as a homing signal to find prey.

Tent caterpillars, including the eastern and forest tent caterpillars, produce prodigious amounts of feces. During the height of their infestations, the sound of their fecal pellets dropping to the ground is so noisy that anyone standing near an infested tree easily confuses it with the sounds accompanying a moderate to heavy rainfall. I can personally attest to how unnerving it is to find oneself in such a place, on a dry, sunny day, surrounded by the deafening sounds of a heavy rain. I have long believed that the natural predators of these caterpillars are quickly and efficiently vectored to their infestations, both by the sounds produced when their fecal pellets strike the ground, and from their odor as well. And, as with the puss caterpillar, the odor is not what we humans think feces should smell like, but is overwhelmingly herbal in nature, being comprised mostly of undigested leaf matter. In any case, it is typical of such infestations to be arrested by the natural predators they attract, so long as they are not checked by the importune application of commercial pesticides.

But what about tea? Is there a connection between the odor of puss caterpillar feces and the fragrance of dried tea leaves? Tea, it happens, contains chemicals that attract a variety of insects. Verbenone, a pleasant-smelling bicyclic ketone terpene, is produced by many plants, including tea (Camellia sinensis) and, presumably, yaupon holly (Ilex vomitoria)–which, by the way, has a long history of being used in the preparation of teas. Verbenone is also used as a socio-chemical, or pheromone, by insects such as the pine bark beetle. When present in small quantities, it may attract them, but it is known to be strongly repellent when present in concentrated amounts. Apparently, pine bark beetles express verbenone in their feces. The amount of verbenone expressed helps foraging beetles distinguish between relative concentrations of the pheromone as evidence that (1) the affected tree offers a good source of food that is not yet being exploited to its potential, or (2) too many beetles are already there to provide much food to newcomers.

But, back to the present study: by the fourth day, two of the caterpillars had pupated (see the photo, below), and four had ceased feeding, dropping to the bottom of their rearing containers, where they appeared utterly lifeless until examined under the microscope.

Enter The Maggots…When two of the latter four–all of whom were quite dead–were examined microscopically, I noted that parts of their bodies moved sporadically. Looking closely, it was possible to make out the head of another organism just below the translucent skin of the caterpillar’s ventral body. Immediately some of my past studies, involving nematode parasitism of wax moth larvae, came to mind. The similarities are intriguing, inasmuch as the cadavers are preserved by an agent supplied by the parasites, and do not putrefy, but so are the differences. Nematodes are tiny worms, while these appeared to be large, slug-like maggots. The endoparasites inside the caterpillar cadavers were, from all indications, some kind of insect larvae.

The four dead caterpillars were transferred to a vented morgue receptacle, and monitored carefully. The next day a maggot was found in the container, with a trail that led directly to one of the four corpses. Another maggot was found in one of the other rearing containers, having emerged from a caterpillar that had died since the previous examination of the container. The maggots were transferred to a parasite container, where they quickly pupated in the capsular puparium typical of ordinary houseflies. The next day 19 caterpillars had died. By the eighth day a total of 84 caterpillars had been placed in the morgue container (which continued to evidence none of the odors coincident with putrefaction), all apparently having succumbed to parasitic infection. A total of 73 maggots eventually emerged from the cadavers, each rooting through the collection of cadavers before pupating–usually within an hour or two.

At least one of the puss caterpillar’s natural predators seemed to be making itself known.

The Maggots were Tachinid Fly Larvae…True flies are classified in the insect order Diptera (a New Latin word formed from the Greek words di = two and pteros = wings, thus “having two wings“), because–with a few obscure exceptions (e.g., the Strepsiptera; strepsi = twisted, and pteros = wings, thus “having twisted wings“)–they are the only insects whose winged forms have, instead of the normal complement of four, only two wings. The two missing wings (forewings in the Strepsiptera, hind wings in the Diptera) remain as vestigial structures–halteres, used to help stabilize them in flight–that neither resemble wings nor function directly as flight facilitators.

Tachinids are related to, and look a lot like, common houseflies: We’re all familiar with the “nasty” common housefly, Musca domestica, and a host of troublesome mosquitoes (also true flies) that make us miserable in the summertime. Houseflies and mosquitoes serve as efficient vectors of noxious, dangerous diseases. It is natural, then, to think that the only good fly is one that is dead. Yet, many–if not most–of the more than 240,000 other species of flies are beneficial, at least in their larval stages, and make human life more comfortable and healthy. Many, for example, are insect-parasitoids whose adult forms look so much like ordinary houseflies that they cannot be distinguished from the latter with the unaided eye. Unfortunately, in their adult forms they favor sugary liquids–the way ordinary houseflies do–so, alas, they become annoying pests when they invade our barbeques, picnics, and homes in search of food.

Fig. 2-1. Insect-parasitoid larvae (maggots) prior to pupation: The image on the left shows an insect-parasitoid maggot that is emerging from a puss caterpillar (Megalopyge opercularis) several days after it killed its host. The image on the right is of another insect-parasitoid maggot during the first hour after emerging from a puss caterpillar cadaver. Within the next two hours, this maggot pupated, after traversing its holding container, apparently seeking a soft substrate in which to bury itself. Under normal conditions, the maggot would dig into the soil, which provides some protection against parasitic wasps that often attack diptera puparia.

Dipteran Parasites: Several dipteran parasitic families are apparently involved in preying on the puss caterpillars collected at the infestation site in Temple that was involved in this study. The dipteran family Tachinidae (a New Latin word, from the Greek tachinos = swift, fleet, derived from the Greek root tachos= speed, thus “speedy”), one of these families, is comprised, in North America, of over 1,300 species. More than 8,500 species have been described worldwide. Most, if not all, of these flies are parasitoids. That is, they kill their hosts, as opposed to true parasites that maintain a kind of uneasy relationship with their–one presumes–less-than-amused-but-still-kicking hosts. Tachinids attack other insects, particularly caterpillar larvae of butterflies and moths. They often lay their eggs on leaves where the caterpillars feed. I recalled, then, how I had noticed the fast-flying flies darting into and out of the yaupon shrubbery at the collection site…

How they Infect Puss Caterpillars: The eggs of some tachinids are so small that they are ingested, undamaged, by the caterpillars. Others lay larger eggs, sometimes after they have matured in the mother fly so they hatch as soon as they are laid, and in other cases the eggs hatch inside the mother fly, who gives birth to live young, and the larvae then lie in wait, ambushing the caterpillars and gaining access to their bodies. They do this either by chewing through their integument or by invading ordinary orifices, such as their spiracles. The tachinid larvae, once inside the caterpillar’s body, feed on the host’s tissues and body fluids. This typically kills the caterpillar within a few days. Later the maggots either pupate inside the host’s cadaver, or emerge to burrow into the ground to pupate.

In the study I conducted with puss caterpillars collected in Temple, Texas, in October and November of 2009, all the parasitoid larvae observed (including some, yet unidentified, that were first thought not to be tachinids, but that are now recognized as defective puparia) emerged from the puss caterpillar cadavers to pupate. The tachinid puparia they produced (several, along with a tachinid maggot that recently emerged from a puss caterpillar cadaver, and one unidentified pupae, are shown below) are identical to those of the domestic housefly.

Fig. 2-2. Insect-parasitoid puparia, and a maggot prior to pupation: Note the wide variation in size between the various puparia shown here. Most appear to be essentially similar in form, though one, in the lower left quadrant of the photo, is very different (appearing more as a chrysalis than a pupa). Eleven pupae, out of a total of 73, followed this form, while the rest conformed. In the months following, nearly all the conforming puaparia eventually produced mature flies, while none of the non-conforming ones did. My tentative conclusion is that the non-conforming puparia were defective.

Certain Tachinids Emerge from their Puparia within Days:A few days after pupating, adult flies began to emerge from the tachinid puparia. These flies (see the montage of one specimen, below) resembled, in their gross anatomical features, ordinary houseflies with a few important, yet somewhat esoteric, exceptions. Their abdomens, for example, are covered with dense bristles, particularly at their posterior ends, and the scutellum (the posterior extension of the mesonotum) is elevated by a conspicuous post-scutellum that is rather small in most other flies.

Figs. 2-3, 2-4, 2-5, & 2-6. A tachinid fly: Note the bristles on the mesonotum, and on the dorsal posterior abdomen, characteristic of the tachinid fly.

The head of the tachinid is similar to that of the common housefly, too, but instead of sponging mouthparts (which in the housefly facilitate the spreading of disease) the tachinid has sucking mouthparts that are used to secure nectar from flowers, a favored source of food for adult tachinids. Thus, unlike their nasty brethren in the Muscoidea family, tachinid flies are not known as vectors for any of the diseases that affect mammals. It is frustrating that these helpful insects can be such annoyances in our homes and around our barbeques and picnics, even if they do not spread disease. There must be ways to resolve that dichotomy, and learning more about tachinid fly biology will go a long way toward finding some. From early March through October, throughout Texas, much of my time is occupied with the taxing drudgeries of fly control in and around hospitals, scientific laboratories, nursing facilities, and medical clinics. Many of those flies are not houseflies, but beneficial tachinids, but that does not matter. One fly–regardless of species, inside one of these facilities, is anathema. But I digress…

Figs. 2-7, 2-8. The tachinid fly head, under magnification: The anatomical structures of the head are diagnostic of the various genera and species within the dipteran family Tachinidae. In the photo at left, the normal tachinid fly head is portrayed, as would be expected in a fly that has successfully extricated itself from its puparia. In the photo at right, the fly attempted to emerge from a puss caterpillar pupa, after successfully emerging from its own puparium inside its host; the balloon-like structure (the ptilinum) projecting forward of the face is used by the fly to rupture the pupa, and evidently was also used to assist in emerging from its host’s pupa as well. This particular fly failed in the latter work and died, its head projecting outside the puss caterpillar pupa, and the remainder of its body still inside. Note that the ptilinum has not retracted back into the forehead, as occurs rather quickly under ordinary circumstances, following emergence from the fly’s puparium, but remains partially inflated in front of the face.

Taxonomical distinctions between the various genera and species in the Tachinidae hinge on anatomical minutiae. After amassing a considerable library of materials on these flies, I had hoped to be immediately able–at the very least–to home in on some of the genera represented in the 70-plus tachinid puparia that were collected in this study. But alas, given the primitive instruments in my lab, and the limited amount of time I can devote to the task, that goal must bend to the sands of time. I shall–for the present study, at least–leave that work to experienced dipterists, and focus on more modest goals. One such is elucidating the life cycles of various species of these flies, as observed in this study with puss caterpillars. Once divined, that should tell us how such cycles affect the mortality rates of their puss caterpillar hosts.

Remember, now, that our experiences in the past indicated that the natural predators of the puss caterpillars are able to exterminate them completely, without the use of commercial pesticides. Yet, when such pesticides are used, neither they nor the caterpillar’s natural predators succeed in exterminating them. As a consequence, a new infestation tends to occur in the following season. This study, besides identifying the natural predators involved, sought to learn why this curious sequence of events takes place.

As noted on the previous page, a large fraction (38%) of the puss caterpillars obtained at the Temple, Texas infestation site had died only eight days into the study, apparently as the result of having become infected with parasitoid larvae. On the 9th day, however, no additional caterpillars succumbed. In fact, as long as the food supplied to the caterpillars was obtained strictly from an un-infested yaupon holly near my lab, no additional parasitoid infections occurred in the collection of caterpillars that remained alive.

By implication, then, tachinid flies do not lay their eggs indiscriminately on yaupon holly foliage, hoping that puss caterpillars will come along for their larvae to infect. On the other hand, the yaupon holly from the Temple, Texas site was likely filthy with tachinid eggs and larvae (a supposition which, in future studies, must be verified from microscopic evidence). In fact, had the trend I observed in the first eight days of the study continued (as would presumably have been the case, had the caterpillars been fed exclusively from yaupon holly collected from the infested site), almost all of the puss caterpillars would have become infected with tachinid parasitoids within the span of a few days more. This, and a number of other observations, suggest how–under ordinary conditions–tachinid flies manage to control puss caterpillars so effectively.

Consider the life-cycles for both flannel moths and tachinid flies:

A. Flannel-moth/Puss Caterpillar Life Cycle:

1. Flannel moths are attracted to a tree or shrub, where they lay eggs that hatch into puss caterpillars. These moths are known to favor yaupon and other members of the holly family, but they are also attracted to oak trees, elms, and sycamores.

2. As the puss caterpillars feed on the foliage, they produce copious amounts of fecal pellets that are comprised of concentrated, volatile plant terpene extractives.

3. As the fecal pellets fall to the ground and collect, their volatile constituents act as pheromones that attract more flannel moths (which then repeat steps 1-3). The remainder of the flannel moth life cycle (not shown in the drawing below) includes pupation of the mature caterpillar–on a twig of the shrub or tree early in the infestation, but on nearby objects when the infested tree or shrub becomes overcrowded as the infestation reaches its climax–and later emergence of the mature flannel moth, which mates with another flannel moth, thereupon repeating steps 1-3).

SUMMARY: The flannel moth/puss caterpillar life cycle begins with a single egg clutch, and builds to a crescendo of caterpillar activity. As their fecal pellets collect on the ground under the infested botanicals, they release a strong aroma of plant-based terpenes. These attract more flannel moths whose eggs keep the infestation going, to the point that huge number of caterpillars are involved. But all this caterpillar activity also attracts a cloud of tachinid flies:

B. Tachinid Fly Life Cycle:

4. In addition to attracting flannel moths, the same pheromones–most likely those that are derived from the puss caterpillar feces–also attract tachinid flies.

5. The  aggregating tachinid flies lay eggs on the foliage the puss caterpillars are eating.

6. As the puss caterpillars become infected by the tachinid fly parasitoid larvae, they die and fall to the ground under the tree or shrub.

7. The cadavers of the puss caterpillars continue to be exploited by the tachinid parasitoids, until the latter fully mature in the larval state.

8. The mature tachinid maggots emerge from the puss caterpillar cadavers, burrow into the soil, pupate, and later (usually a few days during warm weather, but not for months during periods of cold weather, until temperatures warm up again) emerge as an adult flies that mate with other tachinids (whereupon the fertilized female repeats steps 4-8).

SUMMARY: The tachinid fly life cycle begins with the attraction of flies to the terpenes released by the fecal pellets under shrubs and trees infested by phytophagous caterpillars. There they lay eggs on leaves near foraging caterpillars, which hatch and infect the caterpillars. The caterpillars are killed by the tachinid fly larvae, and fall to the ground, where the tachinid fly maggot emerges, burrows into the ground, pupates, and in a few days emerges as a mature fly. After mating, the female lays a clutch of eggs on leaves of caterpillar-infested trees and shrubs. As the caterpillar infestation builds to a crescendo, the tachinid flies increase in a parasitic climax, laying so many eggs that it is impossible for foraging caterpillars to avoid being infected. At this point, two critical things happen: First, the caterpillars become so numerous that they are forced to migrate from the infested botanicals to pupate elsewhere, and this is usually when they first come to the attention of humans (though, unknown to the humans who notice them, most of the migrating caterpillars will, at this stage, be infected by tachinid parasitoids, and thus will not survive pupation). And, second, the soil under the infested trees and shrubs has by now become so rich in tachinid pupae that, when temperatures are right, a cloud of tachinid flies emerges every hour, to lay more eggs and, thus, to decimate the caterpillar infestation at its very peak. If the infestation is arrested by the onset of cold weather, both the puss caterpillar and the tachinid fly overwinter in the pupal state, to resume their life cycles in the spring; but that resumption takes place in an environment rich in tachinid flies (or at least, in their eggs and larvae, recently deposited by tachinids on the leaves of the evergreens favored by the puss caterpillar), which brings the new infestation to a swift conclusion. Though this process is orchestrated entirely by Mother Nature, and generally lies outside the control of mankind, it is difficult, if not nigh unto impossible, to imagine a more effective approach to exterminating puss caterpillars. However, the approach is easily thwarted by man’s application of commercial pesticides that successfully kill the tachinid adults and eggs, and that soak the soil, killing the tachinid pupae buried there, but that fail at destroying all of the puss caterpillars and their pupae.

Fig. 2-5. Puss caterpillar and tachinid fly life cycles: The various annotations are explained in the text.

These life cycles reflect observations obtained from the present study. They extrapolate from those observations the presumption that a common attractant, acting as an aggregation pheromone for both flannel moths and tachinid flies, is involved. That presumption has not been fully tested and verified, though future studies will address it directly to assess its validity.

One puzzling aspect of this study was the discovery that the puss caterpillars I collected at the Temple, Texas site did not appear to have come from a single egg hatch. The caterpillars were quite different in appearance: some were blonde, others reddish in hue, still others light gray, and others a darker gray. Some were uniformly colored, while others showed a subtle or more dramatic stippling of lighter or darker colors. The likely cause of these variations is the occurrence of multiple egg hatches, from eggs laid by several flannel moths, at the infestation site. But flannel moths are far from ubiquitous members of the environment. What would lead these moths to congregate at a single location?

Scatology(the scientific study of feces) is a fascinating field that extends to this project. The fecal pellets produced by the puss caterpillar as it fed on yaupon holly (Ilex vomitoria), when subjected to microscopic analysis, were found to have two interesting attributes; (1) an unusual architecture that provides a significant amount of surface area, and (2) a pungent–but surprisingly agreeable–aroma, expressing the volatile constituents of the yaupon leaves.

The genus Ilex (Latin, from the taxonomical name, Quercus ilex, for holm oak, whose foliage has sharp points similar to those of holly, leading to confusion between them; note, too, the holly-like leaves of Quercus virginiana,the live oak) is the only living member of the botanical family Aquifoliaceae (New Latin, from aquifolium, derived from the Latin roots acer = sharp, and folium= leaf, thus “sharp leaf”), and includes all the hollies, of which some 600 species have been identified worldwide. It has long been known that certain lepidopteran larvae feed exclusively on holly foliage. Humans, besides more recently using holly wood for white chess pieces, have for centuries made teas from holly foliage and stems, to take advantage of their stimulating qualities.

Fig. 2-6. Yaupon Holly (Ilex vomitoria), stems & leaves: This botanical is an evergreen shrub or tree, the latter attaining a height to 25 ft. Leaves are simple, alternating on stems, elliptical and oblong to oval, with crenate margins (the leaves are toothed [dentate] but the teeth are quite rounded, unlike the sharpened teeth of the most famous of hollies, American holly [Ilex opaca]). Flowers show in April and May, solitary or fascicled, producing abundant fruit as shiny, red, semi-translucent, subglobose (not quite spherical) drupes 0.25 in. long. In my locale, these fruits are not present very long, as they are prized by a wide variety of birds. Twigs are stout, rigid, often crooked and short, gray to brown in color, terete (circular when viewed in transverse cross-section), with minute winter buds (as in the above photograph). The leaves and stems shown in this photograph are about the right quantity needed to produce a single cup of yaupon holly tea (in fact, this branch was so used, soon after the photo was taken).

Yaupon holly has been used for centuries, by native American braves, to brew a black tea that is drunk in initiation and purification rites (first described by the Spanish explorer, Cabeza de Vaca, he observed such rites between 1528-1536, reporting on those observations to Spain in 1542); the tea was once thought to cause the braves to vomit, hence the species name, vomitoria. However, recent studies show that the main ingredients in yaupon holly (reported by F. P. Venable in the Amer. Journ. Pharm. 57 (8): 389-90, as tannic acid, 7.39%, and caffeine, 0.27%) are not purgative in nature. Later analyses, according to some reports, have failed to isolate emetics. More to the point, the leaves are presently used as a tea by many Texans, myself included, thankfully without producing the slightest signs of emesis.

Many–though not all–of the plants in the genus Ilexcontain caffeine in their leaves and stems. Yerba mate (Ilex paraguayensis) has a considerable history of being used by natives of south America to produce a stimulating tea, and is now imported to the U.S. for use as a coffee and tea substitute. Guayusa (Ilex guayusa) is similarly used as a stimulant by natives in the Equadorian Amazon; assays have found that its leaves contain a higher percentage of caffeine (as much as 2.0%) than any other plant. It, too, has recently been introduced to the U.S. as a stimulating tea.

Though caffeine is, besides a stimulant, also a natural pesticide that kills many insects, other insects–far from being poisoned–thrive by feeding on caffeine-laced leaves. Apparently, the puss caterpillar is not poisoned by the caffeine found in yaupon holly leaves. In fact, because the caterpillar finds this plant highly attractive, one might presume it considers caffeine a plus in its diet.

I have received numerous reports of puss caterpillars feeding on the foliage of coffee trees (Coffea canephora or Coffea arabica, members of the botanical family Rubiaceae [New Latin, from rubia= red, but in this instance used as a mere type name that has nothing to do with etymological origins]) in Central and South America. It is known, coincidentally, that coffee tree foliage is favored as a food by lepidopteran larvae from at least two genre, Dalcera and Endoclita. Some of the private reports I’ve received suggest that puss caterpillars prefer these trees over surrounding, non-related botanicals, which lends support to the thesis that their caffeine content makes them specially attractive.

Where, then, does this lead us? It is axiomatic that even small details are important in biology. Such details are not accidental. There must be a good reason why the fecal pellets produced by puss caterpillars have such large surface areas. A likely possibility is to provide an expanded evaporation medium that facilitates the expression of each pellet’s volatile terpene constituents. But to what end? Perhaps, to allow those volatile compounds to serve as attraction pheromones that bring more flannel moths to that locale? This makes sense, particularly if flannel moths (adult forms of the larval puss caterpillar) prefer yaupon holly and would, on detecting the odor of terpenes from yaupon holly leaves, be naturally attracted to the source of the odor. If so, their larvae would more easily find mates from disparate gene pools when they emerge from their pupae as mature flannel moths.

Evolutionary geneticists recognize the hypothesis set forth in the Red Queen Principle of Selective Adaptation. This principle tells us, for example, that the natural enemies of various organisms exploit their life cycles to produce more predators. In the present study, the dominant predator is the tachinid fly, and this fly provides a good example of how puss caterpillars are exploited by their natural enemies. Once the attractant accumulates to the point that it attracts tachinid flies to the shrubs or trees that puss caterpillars are feeding on, a predation cycle is initiated that results in the deposition of large numbers of tachinid eggs on the shrub’s foliage. This soon leads to the creation of a soil-based substrate, under the shrub or tree, rich in tachinid pupae.

During periods of warm temperatures the soil-based reservoir of tachinid puparia produces large numbers of tachinid flies, which successively mate and lay eggs on the aerial foliage. In a springtime infestation of puss caterpillars, this would result in a near-complete eradication of the puss caterpillars within the span of a month or two. In an autumn infestation, cool weather often suspends the life cycles of both puss caterpillars and tachinid flies until the next spring, but both cycles resume the moment temperatures elevate, resulting in the effective termination of the puss caterpillar infestation within a few weeks.

The Siren Song of Commercial Pesticides

Man, Are Commercial Pesticides Tempting! Imagine that your yard has just been taken over by puss caterpillars. Your children have been stung, and–because you were not conversant with  the rudiments of puss caterpillar first aid–you’ve just spent several hours and a whole bunch of money at a local Emergency Room. Your spouse blames you, because “You must not have done enough to keep this from happening! ”  Now you’re loaded for bear, and your mind and heart tell you to “Nuke those suckers” with the strongest, most toxic commercial pesticide you can buy. Or, if you have deep pockets and a really irate spouse, you’re ready to call in the professionals, with high -pressure spray rigs that can blow toxic pesticides as high as the tallest tree in the neighborhood, soaking everything in sight, leaving nothing untouched.

I know how tempting it is to do these things. And I’ve had hundreds of communications with individuals who expressed the exact sentiments just described in the previous paragraph. One, for example, was a District Court Judge in New Orleans, Louisiana, whose children had been stung. The judge was used to getting her problems fixed with the snap of a finger, and my advice–to let nature take its course–must have been exceedingly galling.

But attempting to overwhelm puss caterpillar infestations with commercial pesticides only makes a bad situation worse. No matter how much pesticide you spray, some of the puss caterpillars will almost certainly survive. Their tachinid fly parasites, however, being somewhat more fragile, will not fare as well. The commercial pesticide will kill most, if not all, of the tachinid flies. Furthermore, as the pesticide soaks into the soil, it kills the tachinid pupae buried there, and will make the soil toxic to arriving tachinid maggots. Strong smelling pesticides mask the smell of the terpenes in the caterpillar fecal pellets, so tachinids cease to be vectored to the caterpillar infestation. Under these conditions, a parasitoid climax cannot possibly occur. As a result, puss caterpillar infestations at this location can continue for several seasons. Though–owing to the effects of the commercial pesticide–it won’t be as large an infestation as the original one, it will spawn multiple infestations nearby that are at least as large, and potentially larger, because nothing will stand in the way of their reaching a caterpillar feeding climax.

What about biological pesticides, such as Bacillus thuringiensis (Bt)? Once it was clear that chemical pesticides led to a rebound of puss caterpillar infestations, many authorities began to recommend using Bt instead. There are three reasons why, today, I cannot recommend that course of action. First, only actively foraging caterpillars will be affected by the Bt treatment, most of whom are already infected by tachinid flies (pesticides are usually applied late in the infestation cycle, when tachinid flies have already taken control of the infestation–provided they are able to complete their life cycles). Thus, Bt may kill a few caterpillars, but most would have been killed by tachinid fly larvae anyway. This potentially leaves a large number of caterpillars unaffected byt the Bt. All of those that are not yet infected by tachinid flies will have a fighting chance to participate in an infestation rebound, later. Second, because foraging caterpillars are decimated by the Bt, fecal production stops and tachinid flies will no longer be attracted to the site. And third, the Bt toxin, inside a caterpillar infected by tachinid fly larvae, kills the tachinid fly maggots, preventing a parasitoid climax from occurring.

Waiting for the Puss Caterpillars to Die…

OK, so you accept that it is folly to treat puss caterpillars with commercial pesticides. What next? Read the material at PUSS CATERPILLAR EXTERMINATION, Then contact me and tell your story. Maybe your experience will help improve the material presented here, so others will benefit.

Thanks… And a Request…

For all of you who muddled through and read all the above, kudos all around! I’ll continue to review this material to remove as much superfluous verbiage as possible. In the meantime, please help me with your critical comments and corrections.

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Links:   (1) Puss Caterpillar General Information.    (2) The Puss Caterpillar’s Stinging Apparatus. (3) Puss Caterpillar Extermination. (4) The Puss Caterpillar’s Natural Predators. (5). Puss Caterpillar Stings–Medical Interventions. (6) Puss Caterpillar Stings–Home Remedy First Aid Measures.