The tradition of naming the stingingworms after ancient goddesses who were actually worshipped is probably a manifestation of bigotry against women. Perhaps when these species are reclassified along more accurate DNA studies rather than descriptions of what the different variations look like, this can be changed. Few genera of living things deserve more to be known by the names of the men who've studied them at close range and let any of them live,,,
When these moths fold their wings and behave like smaller moths, which they often do, they might look to a hungry bird as if they were already being eaten by something big enough to eat birds. (While many images of moths are unclaimed, this one isn't. Photo by Robert Packard.)
A surprising trend is that at least two social media users who claim "Diana" as their real name have adopted Diana's Buck Moth as a mascot. I suppose women called Diana can't all use the beautiful Diana Fritillary butterfly, or any of the styles associated with the still lamented Princess of Wales...People acquainted with young Hemileucas describe them as nasty, horrid, disgusting, loathsome, and evil. This web site observes that, although this genus of moths undoubtedly does contribute something to the world--perhaps, as a food, it preserves the species' genetic diversity and thus their survival ability, for some of the tiny predators that are able to eat stingngworms--the Hemileucas' contribution to most of the places where they are found is negative. They're not missed. People enjoy being in places where they've gone extinct.
We can skip Hemileuca chrysocarena, or H. hera chrysocarena, or Hera chrysocarena, because it's generally been regarded as the same thing as H. hera. We can skip H. conjuncta, because it's been shown to be the same as H. burnsi. We can even skip the interestingly named H. denudata, because it's turned out to be a variant of H. eglanterina with an especially thin coat (often "denuded") of scales on its forewings. (All the Hemileucas show some tendency to have thinly scaled, translucent wings.) Not much has been written about any of those species because they've not been accepted as separate species for long. Much has, however, been written about H. diana.
However, because those who count diana as a species have evidently had some difficulty finding and photographing it, not many available photos are confirmed as being H. diana. Inaturalist has some charming ones of the furry, butterfly-size moths perching on a naturalist's hand, but refuses to share them. Older books and magazines that list diana have drawings or no illustrations. The most detailed article about H. diana on the Internet seems to be one Tuskes wrote for the Smithsonian Institution; viewable online in a clunky format, it has black-and-white photos of habitat, eggs, caterpillars, pupae, and dead moths only. Moth Photographers Group and Butterflies And Moths of North America agree: "Photographs are needed for this species."
Photographs that look like diana are plentiful but most of them turn out, on close examination, to be one of the more common Hemileucas that look similar.
In 1986, P.M. Tuskes summarized the relationship between diana and grotei:
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The primary host plant of Hemileuca diana in Arizona is Quercus oblongifolia, Mexican blue oak. Adult flight records extend from August to late November, but peak emergence is in October. The primary host plant of H. grotei in central Texas is Quercus fusiformis, live oak. Adult grotei fly from late October to December. Adult Hemileuca grotei from New Mexico are similar to those from Texas. Immature stages and adults of both species are illustrated, as is the holotype of H. diana. Although closely related, hybrid matings between these two species do not produce viable ova.
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They can look alike; both grotei (or grotei grotei) and diana (or grotei diana) are variable in the same ways. They normally live in different places. When they do meet, they look and smell alike enough for mutual attractions to occur. But they don't actually crossbreed. The definition of species differences we all learned in school is that, if living things belong in the same genus but in different species, they can crossbreed, but their offspring may be sterile or have other survival disadvantages. Then again, there are human couples who can't have children together, or whose children are unhealthy, although they could have children with other people...nobody disputes that both halves of those couples are human.
Can that much variation be produced by diet alone? With Hemileucas almost anything seems to be possible. The single white stripe in the typical diana wing pattern can be wide, narrow, broken up, or almost completely missing. Hemileuca means "half white" but some moths in this genus show little or no white on their wings. The background color can look gray, brown, or black. If more entomologists read fashion magazines they'd describe many individuals as "taupe." In short, diana looks almost identical to H. maia, but seems as if it would be more closely "related" to half a dozen other species than it is to maia.
The moths show no color prejudice even when it might serve their reproductive purposes. Sterile pairings have also taken place, with minimal human interference, among diana, eglanterina, electra, and juno. The moths are attracted to one another but their eggs won't hatch, or, in the case of a diana--electra crossbreeding experiment, the eggs hatched into confused caterpillars that didn't eat any of the parent species' typical food plants and therefore didn't live long. Similar results could be expected if diana ever naturally had any contact with the predominant Hemileuca species from the Eastern States, H. maia; the moths look alike but their habitats don't overlap, and their food plants and caterpillars are different.
Nature limits the big silk moths'' ability to reproduce by stacking the odds against their success. They don't really have mouths or digestive tracts , and can't eat after pupating. Any flying they do is fuelled only by the food and water they've been storing up since they were caterpillars. And, though the egg-bound females look plump, the Hemileuca moths aren't built to store very much nourishment for themselves. Males are notoriously slim Females don't carry a lot of fat, either. After a male has visited three females, or a female has placed three egg clusters on different twigs, most individuals' lives are over, though a few individuals have mated or laid eggs five times.
Though classified among the "giant" silkmoths, they're hardly gigantic. Each forewing is aout an inch long, so the wingspan is two to two and a half inches.
The species, subspecies, or race diana is found only in chaparral country, sometimes as far west as San Bernardino County, but normally only in Colorado, Arizona, and New Mexico. There is some question whether the ones reported in Texas had been correctly identified in Texas, but the species has sometimes found in Sonora, Mexico. Adult moths fly in the daytime between August and November. Males normally fly around the middle of the day, looking for females. Females usually fly later in the afternoon, looking for places to lay eggs. Though males and females look pretty much alike from a distance, this species lays eggs high in trees, so females often fly higher than males.
Eggs are placed in ring-shaped arrangements around oak twigs; the first batch may contain over 150 eggs, the third batch (or fourth batch, if there is one) only 25. Not all of the eggs will hatch; the brood of young caterpillars may consist of twenty or more, or only a half-dozen. Diana eggs are greenish gray.
Caterpillars hatch in April and eat first oak flower buds, then oak leaf buds, and finally oak leaves. As with other Hemileucas, newly hatched caterpillars spend much of their time clumping together to regulate their body temperatures against the extremes of the climate in their habitat. Hatchlings are black. In the first three instars they stick together; in the fourth and fifth instars they wander about on their own. Young caterpillars don't usually travel much but have been found travelling in a single-file "procession," like the European processionary caterpillars.
Paul M. Tuskes says that, when disturbed, they sometimes raise their head ends and squirm, whipping their heads back and forth, in a display usually thought to be confusing to birds. Since even baby stingingworms are covered in stinging bristles, for them this may be a true threat display. Many harmless caterpillar species that live in family groups use this kind of synchronized squirming to discourage predators.
Although the bristles contain venom, reckless people have posed holding these caterpillars up on their fingers or hands. This is dangerous because, like all the big silk moth larvae, the caterpillars are clumsy. Short legs in proportion to their bulk, and probably discomfort caused by internal parasites, often cause them to fall out of trees. The feet tickle harmlessly, as other large caterpillars' feet do, rather than sting but there is never any guarantee that these caterpillars will stay upright on their feet.
All stingingworms sting but the effects of being stung vary. The damage seems to depend on how many of the little branching spines penetrate and/or stick in a person's skin. When the branching bristles are found at different distances and angles relative to the body, relatively few tips puncture the skin of a person who makes contact with the upper side of the caterpillar, so the effect of the venom may be only mildly irritating for an hour or so. If the whole caterpillar were crushed against the skin--which can happen, because caterpillars are witless nearsighted animals who probably can't see a human body well enough to realize that all its different surfaces are part of a whole living thing that might be dangerous, and they have been known to explore inside gloves, shirts, and boots--pain might last for weeks. Hatchlings have single spines without the extra barba in the bristles; bigger caterpillars can deliver more venom to a bigger skin surface.. Species in which the branches form tufts of even lengths rather than branches can inject much more venom so, if it's any consolation, Automeris are likely to do more harm than Hemileuca.
Do they know they're stinging? It's hard to say. We know caterpillars don't have the kind of brains that process thoughts in the way humans, or even warm-blooded animals, do. Their stings don't bother the siblings who clump together to keep warm on a chilly desert night or cool on a scorching desert afternoon. Bigger caterpillars look for more space to forage but still seem immune to one another's venom. Under stress, like falling or being prodded with straws, many stingingworms do curl up into balls with their stings facing out, but this seems to be a reflex they share with harmless species. Since many caterpillars don't even have enough hair to make their backs unappetizing to birds or mice, the reflex is probably to protect the face, Protecting the head does not necessarily prolong a caterpillar's life so, if it were possible to ask caterpillars why they curl up, probably they'd all say "I don't know why, I just do." Stiff bristles absorb whatever impact shock an animal as small as a caterpillar feels when it falls, and make it harder to crush stingingworms with a stick. No voluntary activity is noticeable when a stingingworm stings; the caterpillar doesn't know, as it falls, whether it's landing on a rock, on an animal with thick fur that keeps the caterpillar's stings away from the animal's skin, or on a human's bare vulnerable face. It's not even clear whether stingingworms notice when their stings break off in someone's skin; if they feel anything when that happens it seems likely to be like the way humans feel breaking a fingernail.
So it's likely that stingingworms, like extroverts and people who smell unpleasantly of chronic illness, have no idea how why they are loathsome. To one another they seem nice. Hemileuca moths are in the minority of moth and butterfly species who embrace and caress each other while mating. They can mate back to back or side to side, protecting their wings as most moths and butterflies do, but when they can cuddle and express appreciation of their mates they usually do that. Strange as it seems, these literally horrid animals might well agree that they are very nice (to one another), and all the other lifeforms who think they're nasty are prejudiced and mean.
The moths are subtly colored. The caterpillars can be among the least colorful of all stingingworms, in some situations the best camouflaged and thus the most likely to release venom into someone who touches them unintentionally. They start out black; white speckles on the skin and tips on the bristles develop as they mature. The white speckles usually form lengthwise stripes of lighter and darker gray on fifth-instar caterpillars, and a general pattern of striping has been described, but the pattern is not always conspicuous.
This photo is claimed by Valerie G. Bush. Google has other phots that are very similar but not identical.
Caterpillars usually molt through five skins between April and June, and pupate in June, but sometimes, for reasons unknown, they go through a sixth skin and are still crawling about in September. Scientists have theorized that it may have survival value for this species, and other Hemileucas that are exposed to harsh weather conditions, to have a mix of individuals with a normal one-year life cycle and individuals with a two-year cycle; caterpillars that don't pupate between June and August or September may pupate through the winter and fly next August.
Nothing big enough to have to bite into that bristly exterior would ever want to eat a stingingworm. Dozens if not hundreds of harmless caterpillar species mimic the stingingworms' looks, for that reason. However, stingingworms do have predators...tiny ones, that burrow into the flesh nderneath their bristles. They are very vulnerable to internal predators. At least one book has been written about the different predators that thin the populations of Hemliceuca and Automeris caterpillars. If you really want to read about the tiny flies and wasps that keep most stingingworms from becoming moths, here is a mini-book about them:
Like the hornworms in the genus Manduca, stingingworms are big enough to harbor a few dozen internal parasites until the micro-predators eat their way out through the skin and ride around stuck to the host caterpillar. Stingingworms have been photographed with brachonid wasp pupae braced in between their bristles. These parasitized caterpillars continue eating and, in the case of stingingworms, stinging anyone unlucky enough to touch their bristles, but they are never going to become moths.
Nevertheless, despite the help of the micro-predators, many Hemileuca diana larvae pupate in June and emerge as moths in September. Pupae hide in dead leaves on the ground and are relatively easy to kill if recognized. When the moths emerge, they crawl up the nearest bush or tree and wait for their wings to expand. During this time, every beat of the female's tiny fast-moving heart is pumping out the distinctive scent of her species. Humans don't actually smell it, but moths do. Usually a female moth has just time for her wings to become usable before choosing a mate. She may be surrounded by dozens; she chooses hastily. Reproducing the species doesn't take long, but the chosen male and the female may spend a half-hour or an hour exchanging compliments before and after the eggs are fertilized. Then the female sets off in search of suitable places to lay her eggs, and the cycle begins again.
If there is any benefit to the individual caterpillars who go through the extra caterpillar skin, crawl all summer, pupate for most of a year, and start flying next August, scientists have not identified it yet. Sixth instar larvae aren't much bigger than fifth instar larvae, and look just like fifth instar larvae who forgot to pupate when their siblings did. The longer life span may compensate for some disadvantage in the development of the young caterpillar but it's not yet clear how.
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