Moths in the genus Hemileuca were traditionally named after goddesses until the list of goddess names from ancient European literature ran out. Hemileuca juno is a largish moth that seemed to rate a major goddess's name.
Juno was another ancient "goddess" name that at least reflected an interesting process of ancient thought. After the Romans started learning to write from their Greek slaves, Juno was identified with Hera, the cheated, mistreated, longsuffering "Queen of Heaven." Before that, however, juno seems to have been an irregular variant form of genius. It may not always have been thought of as a feminine form, which would normally have been genia, but it came to be used as one. All places, people, and even interesting things (streams, hills, trees, bridges, government offices) were thought to have spirits; if they were masculine the word for their spirit was genius, if they were feminine it was juno. So Juno could mean any woman's individual personality, spirit, talents, as well as various forces of nature to which people prayed. Prayers, offerings, and shrines honored Juno of Money, Juno of Fig Trees, Juno of Birth, and on and on--even Juno of Ribbons, in charge of holding Roman robes in place, or not, and thus of helping newlyweds build intimacy..
Photo by John Ashley, who says this one perched on his screen door for two or three days before emitting her mating "call" or scent, as Hemileucas do, and being surrounded by four or five males. Female Hemileucas don't usually wait that long after eclosion, so this might have been an older individual seeking a second mate, as the hardier ones do. She might have needed a few days' rest, after unloading her biggest batch of eggs, to feel that the second batch were ready for fertilization. The males would probably have ignored her if a female who had never mated before had been "calling," pumping out scent. Probably, on that day, none was.
These moths are found from El Paso, Texas, to Sonora, Mexico, with the majority of photos available online coming from Arizona and New Mexico. California is outside their normal range but, in the early twentieth century, they were found in San Diego County. Given the close genetic relationships among the Hemileucas, it's possible that the reason why H. juno has been rarely reported from California is that living conditions there cause these highly variable moths to look more like one of the "species" types that are normally found there--that the differences are not "true species" differences, but are produced when genetically similar moths live in different places and eat different food. It may be that environmental conditions in California cause H. juno to grow up looking like griffini or electra. Some researchers now think that only six Hemileucas have enough different DNA to be called distinct species.
Like other moths in this genus, Junos fly in the daytime and are sometimes counted as butterflies. Wings are softly colored, anywhere from light gray to black, and are usually folded Some sources mention that females are more often black and males light gray; others document that color is not a reliable guide to sex for this species--some females are light and some males are dark. Enough of the moths look blackish that "Black Buck Moth" is sometimes listed as this species' (or type's) English name.
Photo from EncicloVida.mx, showing how much some individuals' wing markings can look the head of a bird-eating animal.
Mason_S documented the other extreme of the color scale. This mostly white juno was found in Arizona.
At some angles the broad-shouldered body shape and tightly folded gray wings give these moths a resemblance to annual cicadas, although there's no obvious biological reason why a moth who may at least be distasteful to some predators would benefit from resembling an insect that even some humans will eat. Bodies are furry and often show bright colors. Humans don't seem to smell them, but they communicate with one another by scent. Of the distinctive scents that identify a Hemileuca's species, age, sex, and place in the mating cycle, chemical analysis has found traces of chemicals humans describe as "fresh, clean" scents among the chemicals we don't notice at all.
Females average slightly larger than males. Each forewing is between one and one and a half inches long, giving a total wingspan of typically 2.5 to 3 inches.
Silk moths don't live long as moths. While other moths and butterflies can at least drink liquids, the silk moths have no mouths at all. They live on the food and water stored in their bodies, and they don't store much. For animals that get all their body's fuel from stored fat, male Hemileucas have a skinny body shape. Females look much thicker when they are full of eggs; after laying their eggs they look thin too. They do not always live long enough to off-load all of their eggs.
Photo by Mason_S. Does Juno's face remind you of a longhorned cow, too, or is that only me? Such fat as these moths do store up to live on is mostly on the thorax; the abdominal segments store the eggs and reproductive system.
In conservation terms the species is considered "not rare or in immediate danger, but with some cause for long-term concern." Part of that cause for long-term concern is that humans aren't likely to miss a local population of Hemileucas if the local population is wiped out. Some people like the moths, or have a religious belief that we are meant to conserve all of God's creatures. Nobody likes young Hemileucas, which are commonly called stingingworms. Caterpillars are usually seen as hapless, helpless, if repulsive little animals but Hemileuca caterpillars are commonly described as "hateful," "vicious," and "evil."
Or just as predictable pests that recur every spring:
To be fair, most caterpillars don't seem to see far enough ahead to be able to see a human as a single living thing; Hemileuca caterpillars who drag their stinging bristles under the edges of people's clothes probably think they are exploring some sort of tree. When they're falling they curl up with their bristles out in order to land on their bristles. They know that predators don't want a mouth full of bristles. It's not certain whether they know their bristles are venomous. Each caterpillar's bristles protect it from being stung by its siblings' bristles or crushed or crowded by its siblings, even when they look like a solid mass of bristles all lined up together. It's hard to say whether they know how nasty they are.
Whatever their intentions may be, they certainly are nasty. Contact with the little monsters can cause itching, bleeding, swelling, and rarely, in a few vulnerable individuals, anaphylactic shock. If you are one of the vulnerable individuals, you probably are in the habit of carrying an Epi Pen, and should use it if a stingingworm makes contact with you. Others who first notice that they are in the vicinity of a stingingworm when it gets down their neck, inside their boot, etc., find some relief in applying ice and/or baking soda to the rash. Running sticky tape over the skin can remove any tips of bristles that may be stuck to or in the skin. Some people find additional relief in a nice trip to the mall, some in swearing, and some in putting a stingingworm in a small bottle and slowly pouring in alcohol until the animal stops quivering.
Most people can tell by looking at these caterpillars that not touching them is a good idea. If you want to reduce the local population, a heavy stick or stone is good. Ignore any sales pitches for Sevin Dust. It can have a gratifying immediate effect on one generation of caterpillars, but as it also affects their predators, after one or two seasons "pesticides" always produce larger populations of unwanted species. This "Vicious Pesticide Cycle" is what made some normally uncommon species with low natural viability, like the codling moth "worms" in apples and the earworms in corn on the cob, into major pests.
Some sources say that chickadees and sparrows eat baby Junos. Most of the predators on most stingingworms are smaller than the caterpillars are--tiny wasps and flies that can slip in between the bristles and lay eggs on the caterpillars' back ends, from which tiny maggots will hatch and parasitize the caterpillars. Every little bit helps. We never want to harm anything that eats stingingworms.
Nevertheless Junos have their admirers. They've been featured on record album covers...
In Neo-Pagan lore, they've been identified with Medea as a "vengeful" archetype, perhaps because the color pattern of black with accents of dark dull red suggested the image of vindictive thoughts like smoldering coals. That's in an unfinished, not properly published, document by the late Theodore Sargent. Ancient Pagan lore came from cultures where people had limited experience of the world, where they seem to have recognized only a few local species of flowers, birds, butterflies, etc. Sargent's vision was to expand this to reflect contemporary Neo-Pagans' ability at least to Google all the species on Earth. Neo-Pagans often refer to archetypes and images from around the world, and Sargent wanted to link each one to a specific species of plant and of moth or butterfly. H. juno was the only one of the Hemileucas he had placed on his list.
Moths normally fly in November but may be seen any time between September and December. Typically they eclose (emerge from their cocoons) early in the morning, mate by mid-afternoon, and lay the first batch of eggs in the evening. Males fly to where they smell a female and compete for her favors, apparently by grabbing at her or crowding up close to her until she makes a move toward one of rhem. After mating females fly about for a few minutes, presumably just to ripen the eggs if they are perched on a host plant but feel a need to fly anyway, and then place their eggs in a cluster on a twig.
Photo by Cwmelton, who notes that it was taken in Arizona, in November, about 4200 feet above sea level.
Most moths and butterflies probably mate only once. Those who are fortunate enough to live so long will mate again if they can; by the second day of a moth's life it is "older," and less desired as a mate, because fewer eggs will be produced and fewer of those eggs will hatch, but some silk moths mate three times or more. Moths don't expect any loyalty from their mates; if they have the opportunity to mate more than once, both males and females will prefer a younger mate/ It was not Hemileuca juno moths some researchers tested by saturating an object with the scent of a virgin female moth and watching male moths make fools of themselves, drooling over an object that didn't even look like a moth and ignoring a few actual older female moths...but probably most moths, including the females, are about that stupid.
Despite this lack of loyalty and commitment, Hemileucas are "cuddly" moths. They hold no records for snogging time--some of the bigger silk moths spend whole days cuddling--but they do spend time touching, smelling, and looking at each other before and after the act of egg fertilization. Couples often spend as much as an hour just enjoying their mates' company. Sometimes they mate face to face around a twig, the bigger moth tenderly enfolding the smaller moth's wings between (usually her) own. Mating side to side, not showing predators when they're in a vulnerable position, is perhaps typical for this species.
When the eggs hatch, next April or May, the baby caterpillars seem instinctively to know that staying in a cluster works for them. Their bristles maintain a good healthy distance between them without doing them any harm.
Photo by Bob Barber, New Mexico, April 2006. To them the feeling of a sibling's bristles against their own is probably comforting. They've got one another's sensitive undersides. Barber calls attention to the fact that these Junos seem to be sticking together into their fourth instar, by which time other Hemileucas would have gone off to seek their fortunes.
Newly hatched Juno caterpillars are black. The red warts and rosettes appear later, and increasing amounts of white spotting gives them more of a grayish, bark-camouflage look as they grow bigger. They can look very similar to mesquite twigs. As a caterpillar H. juno can easily be a major nuisance--well camouflaged, covered in venomous bristles, with the flattened rosette shapes that allow the maximum number of bristles to stick in the skin of whatever the caterpillar touches.
Photo by Bob Barber, who found it in New Mexico in May. https://bugguide.net/node/view/281210
So long as nobody tries to "control" these horrid creatures by spraying poison on them, they don't seem to overpopulate or do much damage to tree populations. They normally eat mesquite and usually leave food crops alone. They may also eat locust tree, paloverde, or cottonwood foliage; at least people have reported seeing them nibbling on these leaves. It's not clear whether they can survive on these alternate diets or, if they do, whether they will look like juno. It is known that some Hemileucas will grow up with a radically different look, and their ability to mate and produce offspring may be affected, if their diet is changed. Juno larvae who grow up to look like junos, mate with other junos, and produce healthy baby junos, eat mesquite leaves.
Just before pupation, caterpillars often explore plants and trees they don't eat, which are places where their predators are less likely to look for them. This is when stingingworms typically invade gardens and orchards. They spoil the fun of picking fruit, and they don't even eat fruit tree leaves.
By the first real heat wave of summer they start to pupate. Unlike some of the Southwestern Hemileucas, they are said to spin cocoons, though, like those other Hemileucas, their pupation survival strategy seems to be to lie on the ground among the leaf litter and hope that nothing else notices that they are alive.
Most spring caterpillars will eclose in the fall, living six to eight months altogether, but (for no obvious reason) some Junos stay in the pupal stage for two years...or three or even four. These individuals may just be the type who want to be different. They probably also keep the family alive through years of unfavorable weather, and may improve the gene pool by carrying genes through a few extra generations. Like human eccentrics who "always want to be 'different'," they are probably more useful to their families than their families know.
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