The first four moth stories have been funded! Send $5 for each subsequent post about a moth in the genus Hemileuca.
Caterpillars are sneaky, deceptive, confusing animals. Most are small, and try to look like twigs or leaves. Some are too big to hide, and parade around trying to look like snakes or lizards, or just advertising to birds how unpleasant they'd be to eat, with knobs and bristles of extra skin, prickly or choking-thick hair, and color schemes that advertise to birds that the caterpillar ate some kind of leaf that tastes nasty or is poisonous to birds. Then there are the ones who try to be mistaken for the toxic ones; they'd be more digestible, or less indigestible, but they benefit when birds do not realize this.
The moth genera Hemileuca and Automeris are among the most confusing. These are fairly large moths, in the silk moth family/ Caterpillars usually grow about two inches long, sometimes a little longer. While many kinds of caterpillars display bristling spines that look hard for birds to swallow, and often are, most of these bristles are harmless hairlike structures. Some of the bigger silk moth caterpillars have harmless bristles that mimic those of Hemileuca and Automeris caterpillars, because, though these genera are smaller, their bristles have sharp points and contain venom. The venom causes allergy-type reactions in humans. Usually the reactions consist of harmless skin irritation, but, like bee stings, they could put a particularly sensitive person in the hospital. There are survival advantages for many harmless species in looking like the Hemileuca and Automeris caterpillars, which are also nicknamed stingingworms, asps, or pugs. And the Hemileuca and Automeris moths themselves have a wide variety of looks. The caterpillars live in clumps when they're little, and different looks are observed within a single clump.
This one is annulata, too. The range of variations is so wide that scientists disagree whether one type of moth in this group, which some call Hemileuca annulata, is a subspecies of Hemileuca eglanterina or actually belongs in the Automeris genus. Seriously. It can look so similar to another Hemileuca moth that it doesn't need to be classified as a separate species, or so different that it seems to belong in a whole separate genus? Now that's confusing.
As a result of this confusion, while there's no shortage of photos of "Western Sheep Moths," there is reluctance to identify them positively as annulata.
The species name consistently given to these moths, annulata, simply means "ringed." It has been given to several kinds of plants and animals. Hemileuca annulata, or H. eglanterina annulata, or Automeris annulata can be described, as all moths and butterflies can, as shaped like a tube made of ring-shaped segments. It can also have conspicuous ring-shaped markings, on the moth's wings, and even on the sides of the caterpillar. Note the half-rings along the sides of the annulata shown at
Not that all of them have this pattern, or any other pattern, of conspicuous markings. Hatchlings, scientists confidently say, are black. As they grow and molt they display markings, which can be white, yellow, or pink, or remain black. The bristles may be gold-toned. Scientists have not found a consistent pattern to predict how an individual stingingworm is going to look.
They are better camouflaged, and more likely to be noticed by humans showing the "YeeOWCHHH what was THAT?" reaction pattern, when they stay black throughout life. They may, like some butterflies, tend to show more dark color if exposed to lower temperatures, more light color under warmer conditions. Caterpillars in these genera are the ones people describe as "nasty," "vicious," and "evil." They do not show much evidence of consciousness. They don't think through their problems. Instincts tell them, when disturbed in any way, to curl up in a ball with their stinging bristles outward and drop to the ground. They don't know whether they're being attacked or not, but their reflex reaction could be described as an "If there is a predator, inflict as much damage as possible" pattern. (They are light enough, and their bristles are firm enough, that falling fifty feet out of a tree and landing on their bristles doesn't seem to hurt them.)
"There is no single rule for separating...eglanterina, annulata, and other populations," one scientist observed in Tuskes, Collins, and Tuttle's Wild Silk Moths of North America. If the different types of moth in this group are distinct species, they hybridize freely. They are large moths that typically fly in the daytime and aren't attracted to light at night. The moths, like the caterpillars, show some combination of black, white, pink, or yellow colors.
A photo essay studying one individual annulata, with particularly clear and gorgeous black rings on its pinkish white and bright yellow wings, appears at https://www.argentinat.org/taxa/1026499-Hemileuca-eglanterina-annulata/browse_photos .Our featured photo (at the top) appears on several other pages but seems to have come from this collection.
The big silk moths don't eat. They live on the fat they stored up as caterpillars. They have only days to find mates. Males are attracted to the scent of females, which humans don't seem to notice. Females usually choose a mate after their wings have expanded but before they fly. After mating the female moth usually lays her first and biggest batch of eggs on the branch where she crawled out of her pupal skin to spread her wings. Then she flies off to find more twigs and lay more eggs. A female will tpically lay three batches of eggs, sometimes more, with fewer eggs in each batch. Meanwhile the male may mate with three or more females if he can, and he also produces fewer viable sperm each time. Then their energy is spent and their lives are over. Scientists can easily pick male moths off the cage in which a female is confined. If the moths can get together to mate they are, like some of the real giants in this family, in no hurry. "Dum vivimus, amamus," they nonverbally say. Annulata couples like to snuggle for anywhere from thirty minutes to two hours. They probably experience their lives as very romantic.
Egg clusters are big enough for humans to find the clusters on tree branches and pick them off trees we want to protect, but the branches chosen may be too high to reach easily or may be concealed by foliage. Female moths usually try to lay their eggs on plants their larvae will be able to eat. Since the moths in this group can eat almost anything, they don't need to be particular about where they lay their eggs.
In the warmer part of their range (Alberta to Argentina), especially, caterpillars in this group are likely to hatch during North America's winter months. Having black skin and sticking close together in groups may help them keep warm when the days are mild and the nights are cool. Their slow growth rate and relatively long lives may have something to do with their living in dry climates (they succumb to fungus infections in damp weather) and going into hibernation mode at night. If the group are disturbed they may start wagging their heads; the movement may persist until the whole group are oscillating, presenting a confusing target to predators that might want to grab a head, and increasing the probability that the said predator will bump into their spines.
How bad is the sting, and are some species' stings worse than others? Answers to this question cluster around entomologist David Fine's not very scientific experiment, video-recorded at https://www.youtube.com/watch?v=jv6YApmwo5k . In the video, Fine touches the thumb edge of one hand to the back of a Hemileuca caterpillar and the thumb edge of the other hand to the back of an Automeris io caterpillar. (Io's are easy to recognize by their bright green color; their name comes from a character in Greek literature, probably originally pronounced more like "E-O.") We can't really see welts form, though Fine tells us he can, and have to take his word that the Io sting was much more painful. Some commenters describe much more painful reactions to Hemileuca stings when they inadvertently grabbed or stepped on the caterpillars.
Lightbulb! Hemileuca bristles usually branch around a central spine. A light touch such as Fine did would touch only the tip of each central spine, releasing relatively little venom into his skin, while grabbing or stepping on the caterpillar would bring more skin into contact with more spines and more venom. Automeris bristles are flat-topped, allowing almost all the tips of each clump of spines to touch the skin at the same time. Even a light touch would release much more venom into the skin. So it depends less on the species than on the extent of contact with stinging spines. If stung, rinse with cold water, use sticky tape to remove any spine tips that may stick in the skin, and wait. Call a hospital if anaphylactic shock sets in, since it's curable, but most people have nothing to fear. The pain will subside in minutes or days, depending on how much venom the person absorbed.
As the caterpillars mature and the spines branch more conspicuously, they separate, but as they separate from a central point, where you find one you're likely to find more. They are vulnerable to micro-predators--tiny burrowing wasps that may be starting to eat a caterpillar while it is crawling about. They can hibernate through the winter; in Colorado and further north these moths normally live more than a year, though they spend more of their lives as caterpillars or pupae, and hibernate through much of that time. They normally mature in early summer, pupate in late summer, and fly in autumn. The name "buck moth," widely given to this group, was associated with "buck" deer hunting season
Again, while photos of Hemileuca are abundant, it takes an expert to identify one as annulata. A good clear color photo of a confirmed annulata caterpillar is available at https://repository.arizona.edu/bitstream/handle/10150/609134/dp_10_01-013-030.pdf?sequence=1&isAllowed=y . The photo section is between the main text and the bibliography.
Though they're in the silk moth family, they don't produce much silk. Usually they pupate under a leaf, a rock,or a layer of dirt rather than making a cocoon. After pupating they climb onto a twig to eclose, or expand into their adult bodies and spread teir wings. Then the cycle starts over again.
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