(This is the post that was meant to appear on Thursday, but didn't. Yes, I've been online on the day I usually unplug. No, I'm not giving up my unplugged Saturdays rule. Christians are specifically told to pay our debts before we make offerings. That includes time as well as money.)
Passing over Hemileuca grisea, which has long been considered the same animal as H. oliviae, we come to H. grotei. Next on the list, H. gunderi has long been regarded as the same animal as H. marcata, which is thought to be a subspecies of H. hera. H. harrisi has been classified as a form of H. eglanterina. The next Hemileucas on our list will be H. hera, and then H. hualapai.
Photo by Beth Duncan for inaturalist.org. While this one's body is black, some individuals have a "tail" tuft of bright red-orange hair on the posterior segments, and some have orange-red on the head. The caterpillars can eat a few different species of oak leaves; variations in the look of the moths are probably produced by diet.
Photo by Maddie at Bugguide.net. Both specimens were found in Texas, but Beth Duncan didn't want to disclose which town, to protect the family!
Many people are delighted when a local Hemileuca population goes extinct. I can relate. My local population of H. maia was successfully extirpated during the logging years when most of the oak trees were cut down. As a child I was warned about stingingworms but didn't see one until I was fifteen years old. Instinct told me on first sight that it needed killing. Unfortunately its relatives survived, and H. maia was a great nuisance for the next thirty years. Attempts to stop the spread of Lymantria dispar seem to have got rid of local populations of H. maia, and they certainly are not missed. Still, extinction is forever, and the Hemileucas, easy to hate though they are, may serve some special purpose in the overall ecological system. Perhaps there are valid reasons for letting these moths live in remote wilderness areas, far from human habitation.
"Grotty" as a general word for bad, undesirable, inadequate, unhealthy, etc., is a slang word whose origins are unclear. Maybe someone didn't like grottoes. Some online dictionaries consider "grotty," the earlier and more typically British form, usually pronounced more like "graw-ty," as a separate word from the Valley Girl version, pronounced "grow-dy." The US pronunciation and usage do seem clearly to have been influenced by the slang use of "gross." Though Hemileuca grotei is something any Valley Girl would have agreed was grotty, or grody, to the max, it's not found in the San Fernando Valley. An insect that is a nuisance primarily in Texas and New Mexico seems unlikely to have been the source of one of the most characteristic words in "Val-speak."
In any case, although grotei can sound like "grotty" it's a separate word. Grote was the name of one of the first naturalists who wrote about this species and H. grotei is sometimes called Grote's Buck Moth in English. The fact that baby buck moths, also called asps, pugs, or stingingworms, happen to be bad, undesirable, and unhealthy is coincidental.
There was a tradition, in the nineteenth century, of naming the Hemileucas after ancient goddesses that were actually worshipped, like Diana. Grotei is very similar to diana. Their ranges overlap. The moths fly at the same time, so they can easily meet, and mutual attractions can easily occur. Grotei will mate with dana but, when the species were crossbred in an experiment, the caterpillars didn't live long. To some scientists, that proves they're distinct species. To others it proves no such thing. Two humans may be unable to have children together, but we still classify both of them as Homo sapiens sapiens. DNA studies suggest that grotei and diana might be considered variant forms or races within one species.
There's not a lot of information about Hemileuca grotei online, and much of it overlaps with information about diana, since much of the available literature considers them as subspecies within a single species the authors often call Hemileuca grotei grotei and H. grotei diana. Depending on which search engine you use you might find earlier posts in this series listed as sources, like
Which does contain a more detailed discussion of the relationship between grotei and diana. I'd like to refer readers back to that post because the sources I cited in it came up in a search for diana rather than a search for grotei.
Paul Tuskes, listed as the primary author of the $400 book on silkmoths that allows that there may be only six genetically distinct species of Hemileuca, was also the author of a stand-alone paper that found "no doubt that [diana and grotei] are distinct species." It depends on how we define a species. Although their ranges overlap, and they look similar, grotei is more likely to be found further east; adults are slightly smaller and tend to be darker gray or black; and caterpillars are more likely to show flattened rosettes or stinging bristles rather than branched stalks, meaning that more venom gets into the skin and more pain and swelling can be observed after casual contact.
Male and female grotei look pretty much alike. Females tend to be slightly bigger and darker, but size and color ranges for males and females overlap. Some individuals have a wingspan slightly less than two inches; most measure two inches or more. Females are more likely to be described as black, males as dark gray or dark brown. Museum specimens fade quickly and look just like diana, which is usually gray and white while living.
Actually, even while living they can look just like diana. Photo by Jim Gamp.
Photo by Robert Pearson documents this species' most irritating habit...literally irritating. In this adult moth, curling up when startled serves no purpose; if anything it makes her egg-stuffed body easier for a predator to bite into. (We know she's female because males don't have egg-stuffed bodies; Hemileucas carry very little fat.) Curling up is a reflex that served her when she was a caterpillar. Her stiff bristles absorbed any shock her tiny body might have felt on impact, if she fell out of an oak tree, and also irritated the skin of anyone she might have bumped into on the way down. This is one reason why some observers describe Hemileuca caterpillars as evil. The other is that, when looking for places to pupate, they sometimes explore the crevices formed by clothes, boots, and gloves.
Adult moths usually fly in autumn, being most active in November. As with other Hemileucas, males smell freshly eclosed females and follow the scent. Females apparently pick one of the males watching their wings unfurl. Pairs spend some time snuggling before and after the reproductive act, though they don't bond to the extent of seeking each other out again. If they mate again, both males and females will look for younger mates. This is biologically advantageous since moths release most of the viable gametes the first time they mate; nature has provided for the fact that many of them won't live to mate a second time. Females then fly about, even if they've already found a suitable host plant, for several minutes while the eggs develop, and lay eggs usually in tidy little rings around an oak twig.
Photo by Dalmar Cain, documenting that, like other Hemileucas, grotei prefer to mate face to face.
In this photo by Katittle, the female has barely had time to crawl up from the ground, stretching her legs and wings as she goes, looking less like a grub and more like a moth with every step, and perch on a twig while her wings continue to expand, before the two males started competing for her attention. She really needs to wait for her wings to unfurl before she mates, for optimal reproductive success, but sometimes a girl moth loses her head and mates before she can fly.
Whereas, in this photo by Gary L. Spicer, the moth has had time to unfold her wings and apparently to void her meconium (surplus material a moth or butterfly excretes on eclosion), and no male moths have found her yet, possibly because pesky humans were bumbling about with cameras. Spicer noted that she flew about twenty feet to resume her "calling" behavior. Life is not fair.
Though moths and butterflies communicate with one another primarily by scents, humans don't smell most of these scents. We don't notice grotei having an odor. Spiders do, and some spiders in the genus Argiope are thought to secrete a biochemical that smells enough like a female grotei, to a male grotei, that it lures male moths into these spiders' webs.
As seen at Thepetenthusiast.com, many caterpillars that are not venomous grow relatively soft, blunt, harmless bristles that look like the bristles of stingingworms. Caterpillars do survive by faking out their predators, looking more dangerous than they are. However, Thepetenthusiast messes up badly by saying that "black caterpillars are known to sting." Some are. Most aren't. The majority of North American caterpillars that can have black skin or hair are completely harmless. Caterpillar hair is generally about as irritating as any other kind of short hair; if it gets down your neck on a hot day it will raise a rash, but it's nothing to worry about. In the Eastern States, at least, the Hemileucas are the only kind of caterpillar that looks black for part of its life and can really be said to sting...and many of them don't even look black by the time they are usually seen.
Caterpillars often hatch when their host trees blossom and nibble on the flowers. Since oak blossoms are green and not especially conspicuous to humans, nobody blames the caterpillars for spoiling the look of the flowers. To some extent they do, but they also are thought to help transfer pollen from flower to flower. The trees are also pollinated by wind. No studies seem to have been done on the extent to which these caterpillars help or harm the trees.In any case they seem to coexist.
Hemileuca grotei caterpillars start out black, as many Hemileucas do. The skin keeps some black color but develops increasing amounts of pale gray, yellow, or white spotting and striping with each molt. When looking for places to pupate they tend to look gray. Though H. burnsi looks quite different as an adult moth, in Texas, where grotei eat some of the same food plants as burnsi, the caterpillars can look like burnsi. While Tuskes' research subjects all developed flattened rosettes of stinging bristles, some grotei caterpillars don't, or have some rosette-shaped and some branch-shaped bristles. They can look almost completely white, bluish grey, gray with mossy-green bristles, or even gray with orange bristles. Usually, but not always, they show both lengthwise and crosswise stripes; the colors of some caterpillars can be described as plaid.
Photo by Robert J. Nuelle from inaturalist.org.
Detail shot, showing the pattern of tiny spots that give the caterpillar a "grey plaid" look, by Sallyatticum in Austin in April.
This individual, also from Texas, shows the flattened rosette type of stinging bristles. As shown above, individuals can have some branching and some flattened scoli (bristles) on different parts of the body, branched all over, or flattened all over. Photo by Bill Morgenstern.
Arob2724, a vigilant Texan, thought this individual "looked like a Gypsy Moth larva" but lacked the blue and red dots. Whew-ee. When you live on the Atlantic Coast and have to deal with both species, although yellow-green is a color some female gyps develop in their final instar, you learn to look at the overall shape. Gyps, or Spongeys if we want to be up-to-date (the egg clumps look like fur-covered sponges), have tufts of stiff hair, NOT branching bristles. You can pick a Spongey caterpillar off a tree with your hand. Branching bristles (or rosette-shaped bristles) indicate a stingingworm. You could pick that caterpillar up in your hand, but you would be sorry. Each bristle packs about as much venom as a bee's or paper wasp's stinger. The ones whose bristles form flattened rosettes will bring more bristle tips into contact with the skin, thus delivering more venom and more discomfort.
Evan St Laurent observed this individual over time and posted a series of four photos at https://bugguide.net/node/view/1655523/bgpage / Here the caterpillar's final skin is empty, having sloughed away from the pupa whose tail end is visible above. At the page linked are photos of the caterpillar crawling and the pupa moved out onto the bare sand.
Stingingworms have few predators. Nothing wants to bite into them. However, they are vulnerable to fungus infections in damp weather, and grotei are often parasitized by tachinid flies. "What are tachinid flies and where can I get some?" you may ask. Tachinid flies are smaller than houseflies and have a different look, if you look closely. But you probably can't look closely. We can look closely at houseflies because they buzz around us and our food. Tachinid flies are not interested in us or our food, so they're harder to spot.
Photo of a tachinid fly by Wisconsin Horticulture. There are different species. Yellow wing joints are a feature of some tachinid flies that attack stingingworms. They also attack tomato and tobacco hornworms.
Since humans rarely get a close look at tachinid flies, the easiest way to recognize them is that they don't "bother" us as houseflies do. If we control houseflies by covering things they can eat and swatting the ones that bother us, no worries. Tachinid flies will follow their host species. All we have to do is not poison the environment, and they will take care of both kinds of nuisance caterpillars.They lay tiny eggs on a young caterpillar's skin. As the caterpillar grows up, the eggs hatch out inside the caterpillar. The caterpillar can live with its parasites until they start gnawing their way out and pupating among its bristles. A few parasitized caterpillars have managed to mature into moths, but they didn't reproduce.
There are photos of what parasitized caterpillars look like, online, if you want to look. All I'll say here is that, if you find a caterpillar with tiny white cigar or bullet shapes stuck to it, the caterpillar is not laying eggs--it's hatching tachinid flies.
If the caterpillar lives long enough, it forms a pupa, a dark bare boring-looking object that seems to survive by looking like a pebble or dropping. Pupation normally takes place under some sort of cover, but these moths don't burrow deep into the ground or spin a real cocoon. In autumn the adult moth ecloses, crawls out from under whatever it hid under while it was a pupa, and crawls across the sand looking for a place to assume a vertical position and unfold its wings.
Photo by Clarafrota. Males look like skinny grubs at this stage, females like fat grubs. They will be prettier when their wings unfold, This takes some time. This animal, which looks like a fat grub, was probably a female looking for a plant stem to climb up. During the process of stretching and unfolding into her adult body, the female is actively spraying scent into the air, summoning males. By the time she's able to fly she probably has a few prospects to choose from, and the whole cycle begins again.
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