We already met Hemileuca warreni, last summer. It has usually been classified as a southern subspecies of H. maia. Stingingworms found on the peninsula (not the panhandle) of Florida tend to be more colorful, and moths may average darker in color, than other maia. What's changed recently is that in 2023 some scientists voted to list H. warreni as a separate species and, though most web sites haven't added pages for it, this winter some sites have set up separate pages for the "Florida Buck Moth."
Here's what I learned last summer. Basically this species is a minor nuisance. It is a significant food source for some little tachinid flies and braconid wasps. Its primary food plant is oak leaves, often switching to other plants as the caterpillars mature. It does all of its eating as a caterpillar; moths don't eat or even sip liquid, and don't live long. It's not a threat to any plant but it is a great inconvenience to fruit pickers, as caterpillars often like to spend their final instar as caterpillars infesting fruit trees and bushes. Caterpillars are covered in stiff branching bristles; when startled they drop off their food plants and curl up with all their bristles out. Each bristle tip contains about as much venom as a bee sting and will, like a bee sting, continue to cause pain as long as it remains in the skin. If touched by one of these little monsters humans are advised to pat the affected skin gently with duct tape, sticky side down, to remove any bristle tips from the skin. Once bristle tips are gone, wounds generally heal quickly. Reactions could in theory include anaphylactic shock; in practice it's very rare for anyone to report symptoms worse than a painful skin rash.
The name "stingingworm" has been applied to Hemileuca maia at least since colonial days, though caterpillars are not, technically, worms and some scientists dislike names for caterpillars that include "worm."
The photos of Hemileuca warreni available online are mostly not new; most of these photos were posted on pages for maia in the past, and have been transferred to pages for warreni as those pages have been set up. The Inaturalist group are leading the way to set up separate pages for warreni.
Photo by Michaeltrestman. Big, feathery antennae identify the male of the species.
His anatomy is a bit unusual. Tufts of fur add to the bulk of his thoracic segments, in which is stored most of the fat on which he lives as an adult. Head and tail segments look tiny by comparison. His little flat head contains eyes and antennae but no mouth, and his thinnish abdomen contains only reproductive parts, no digestive parts, and surprisingly little fat for an animal who can't eat.
Photo by GraceBaffer. The female is similar, though usually a bit larger, only when she emerges from pupation her abdomen looks fatter. This is because she is full of eggs. By all appearances she is eager to unload the eggs as fast as possible. Many individual Hemileucas also show a tendency (if anything, more common in males than in females, though we see it in this female) to lose the feathery scales that give their wings color and texture, so their wings become translucent. In many species the male has red or orange fur on his tail setments and the female has black, white, or grey, but this is not as reliable an indicator as the antenae. Female antennae are simple; male are featherlike.
Most of these moths probably live only one day. Most of the stored energy from all the food they have ever consumed, such as it is by the time they eclose and fly, goes into finding a mate, preferably on that first day of their adult lives. The female actively pumps out a scent (which humans can't smell) to summon males, and males follow that scent, using all those sensitive nerve endings on their feathery antennae to bumble about as they try to follow a scent on gusty Eastern States wind, for half a mile or more.
Photo by Logancrees. Eager to mate though they are, couples of Hemileuca usually take their sweet time and enjoy each other's company for about an hour. Mating back to back is the most common position for moths, but Hemileucas sometimes mate face to face (around a twig). They do not, however, show any interest in each other after mating. Moths are most likely to produce viable offspring the first time they mate so, if both of a couple live long enough to mate again, both the male and the female will look for younger mates.
After mating the male rests for a day or two. He has used up a good deal of his life force and is vulnerable to predators. If nobody else eats him, however, he is likely to regather his energy and flit off in the direction of another female if he can smell one.
After mating the female uses up the biggest part of her life force flying about to find the right place to lay her eggs. Flying seems to be part of the process; if she happens to be sitting on a suitable tree she still flies about for fifteen or twenty minutes. Then she places eggs in a cluster, vaguely ring-shaped, around a twig. This takes a few hours. After laying her eggs she, too, rests for a day or two.
If they enjoy the full week to ten days it's possible for them to live, Hemileucas may mate two or three times. Each time they will produce and release fewer fertile gametes. Each of a female's egg clusters will contain fewer eggs, and fewer of those eggs will hatch.
Hemileuca warreni fly in what most of North America calls winter--the temperate season in Florida--and they also "buck" silk moth customs by flying in the daytime. Most photos of adult warreni are dated in January. Eggs hatch in March.
As they grow bigger the caterpillars become more colorful. First the bristles on the upper back show bright red, orange, and yellow color; then patterns of white, sometimes red, and sometimes orange or yellow develop on successive skins. While they live together and eat the same thing siblings seem at least to show a family resemblance, though their colors vary and they seem free from color prejudice. As they mature they separate and eat different things, and their final caterpillar skins vary dramatically in color. Most individuals photographed remained yellow, black, and white in different patterns, but some are real studies in yellow, red, and orange.
Photo by Mudgiecrabshabistan.
Photo by Hannahwojo. This was the most common color pattern photographed--a mostly black caterpillar with dark yellow rosettes and black branching bristles. White can predominate over black, and branching bristles can be yellow or white. Some aberrant individuals were pale all over, and one had solid reddish-brown skin and brownish-yellow bristles.
Photo by Beach2022. Warreni does sometimes show one real structural difference from other Hemileucas. Their posterior segments taper more; they have only one central rosette-shaped yellow bristle in the next to hindmost ring of bristles, instead of a pair of rosettes, with narrower branching bristles on the sides. However, not all photos identified as warreni clearly show this difference from maia. All photos identified as warreni do seem clearly to show that the central pair of bristles, and sometimes the single central bristle at the tapering rear end, form long rosette shapes at an early age, while maia develop rosette-shaped bristles in the final instar or not at all. Warreni's rosettes are yellowish brown to orange; maia's, if they ever form, are often gray.
Early in the summer the pupal shell pops out of the final caterpillar skin. Although the pupa squirms away from the cast-off caterpillar skin, it does not usually put much distance between itself and its dead skin, and smooth pupae are often identifiable because at the tail end they're still stuck to bristly, empty skins (which still contain venom). The insect then pupates for the rest of the year, finally ecloses, and starts the cycle over again.
So, you might ask, what else is new? Apart from the different spacing of the rosettes, which does look like the kind of structural difference usually considered to identify a distinct species, why does warreni suddenly deserve an article all to itself? It is very similar to maia. All the Hemileucas are very similar to each other. This has been discussed before.
What's new is this report on Reddit: "There were 1000s plus of these guys flying around."
In January? Near Boca Raton, Florida? That has to be warreni. It looks dead but it's probably not. The Hemileucas curl up and play dead under stress, both as caterpillars, when curling up puts their bristles out and makes them formidable opponents for predators that rely on biting to kill prey, and as moths, when the same position displays the juiciest parts of their bodies for easier biting.
And that's bad news. Boca Raton seems to be the social hub of Hemileuca warreni's world--most photos of warreni on Inaturalist indicate that the individuals were photographed near that city--but Hemileucas are usually found by dozens, not thousands.
The city could be building up to the kind of irruption the Southwestern States had with Hemileuca oliviae a hundred years ago. By all accounts it was horrible, and left people with a perception of the Hemileucas as even nastier than they are. Chronically overcrowded and malnourished caterpillars seemed to be consciously trying to sting anything and everything. Gnawing desperately on things they couldn't digest, they were blamed for wastefully, maliciously eating pasturage away from hungry cows and sheep, then "poisoning the land" with their dead bodies when they starved to death anyway. They did ever so much more damage during the years when, apparently due to loss of their tiny primary predators, they were found at ten or twenty times their normal population density--when nubile moths fluttered around one another by hundreds instead of dozens.
Floridians know by now what they must do...or at least the ones who read things on the Internet know. They must resist, must positively fight against, any temptation to spray poison on their stingingworms. They must allow natural predator populations to restore the balance of what is, at best, a deeply unlovable species.
It would be a good idea for the State of Florida to move now, to remove all "pesticide" sprays from every store. (Yes, I know, the mosquitoes. Breathe. Youall may have to live with your mosquitoes to avoid even worse plagues...even a plague of stingingworms would last for only a short season, but a Vicious Spray Cycle with the mosquitoes...) Do not make it possible for anyone to try to "control" stingingworms in a way that will push their population, and other nuisance insect populations along with them, hopelessly out of control.
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