Hemileuca Californica

In the nineteenth century, it was a news item for naturalists that the adjacent states of California and Nevada each seemed to have its own typical species of Hemileuca. The moths, H. californica and H. nevadensis, were almost identical except that nevadensis was yellow and gray, while californica was white and grey. Both were occasionally found as far east as Wisconsin and central Canada, and they weren't hard to get to hybridize, but naturalists out West always seemed to find one moth in one neighborhood and the other in another neighborhood...

Though some of the big silk moths don't fold in their wings as small moths do, the Hemileucas tend to fold in their wings, so this picture may suggest the Meal Moth. Don't make that mistake. Meal Moths are tiny; Buck Moths are not. Though not as gigantic as other silk moths, Hemileucas generally have wingspans from two to three inches across.

As regular readers guessed by now, by the early twentieth century Holland's Moth Book had definitively lumped californica and nevadensis into one species. They are basically one species. A web search yields very little for californica today and, although I found some lovely fair-use photos of the color type that used to be called Hemileuca californica, I found them listed as specimens of nevadensis.

It is sometimes considered a pretty moth.

The female is slightly larger than the male. The wings of Hemileuca moths can have thin coats of scales and look translucent; we can see where fore and hind wings overlap in the picture above.

Moths often fly in the daytime, in autumn. Caterpillars hatch in spring, This one looks less bristly than some other stingingworms do, but in view of the correlation between unpleasantness reported for being stung and the number of stinging tips that make contact with the skin, it may need killing even more desperately than the spikier-looking types. Flattened rosettes are more likely to deliver more venom than branching bristles. 

However, caterpillars can also resemble those of burnsi and electra. The yellow color pattern is the most typically "Californian" but is not necessarily correlated with the californica wing pattern in adults.

When we want to see fewer of a species in a given place...and let's face it, that is the concern most people have with the Hemileucas, though some people do seem to admire these animals...the first rule is NOT to spray poison on it. Well, alcohol kills stingingworms reliably, quickly enough to be considered humane, in situations where there might be good reasons not to whack one with a stick. (In situations where a stingingworm is crawling on an individual, the important thing is to get it to crawl off again without contact between spines and skin. Remain calm. Try to get it to crawl onto a loose end of clothing from which it can be made to drop off, well away from the person.) 

When we spray poisons to kill plants or animals, we also kill their natural predators and competitors. Unwanted lifeforms always reproduce faster than their main predators do, and some isolated individuals always survive a spray poisoning, so spraying the pests away means that in their next generation their population will increase exponentially. Keeping up efforts to control unwanted animals by poisoning has made rare species into real pest species. 

We can, however, reduce unwanted species populations by functioning as predators, even though we don't eat most unwanted species. (People do eat bear meat--and like it.) If you have a real infestation of unwanted insects, and you crush several at once, you may find natural predators eager to help dispose of the bodies. When I've swatted a lot of flies, my friendly neighborhood White-faced Hornets have buzzed up to watch and wait for a chance to remove bodies. I've never found and destroyed a whole clump of stingingworms; at the clustering stage they tend to stay high in trees, but if you did kill a whole brood you might find out what their primary local predator is. There is no need to increase predator populations. Just don't do anything that harms or interferes with them. Natural predators usually control nuisance species nicely wherever humans have not created an ecological imbalance by cultivating unusual numbers of food plants.

Californians are likely to have to deal with Hemileuca californica if they've planted or encouraged several dozen possible host plants. The native species these caterpillars eat are listed, with pictures and tips if you want to encourage them, at Calscape:

https://calscape.org/lep/Hemileuca-nevadensis-(Nevada-Buckmoth)?

Serious problems with californica may occur when several cherry, peach, or almond trees have been planted close together. Every child deserves the opportunity to climb up into a tree and pick cherries. Stingingworms seem to exist primarily for the purpose of turning what ought to be one of children's favorite chores into one they dread and avoid. Separating the host trees helps, but does not completely solve the problem. Still, spraying poisons can only aggravate the insect problems and reduce the value of the fruit. Predator populations will increase in proportion to nuisance insect populations. Flies and miniature wasps are the primary predators on large caterpillars in California.

The friendly tachinid fly is smaller than a housefly, has yellow wing joints, and most importantly leaves people alone. A less general feeder than the housefly, she's not attracted to human sweat. Her microscopic eggs hatch into tiny maggots that parasitize stingingworms, tomato hornworms, and other nuisance caterpillars to the point that, where the flies are free to do their job, the caterpillars are only occasional nuisances. You can attract tachinid flies by leaving crushed caterpillars on the ground, or simply avoid spraying poison and wait for them to move in. Tachinid flies leave eggs on leaves for caterpillars to eat if they don't find a chance to lay eggs on the caterpillars themselves. Either way, although parasitized caterpillars often survive until the tachinid maggots eat their way out of the caterpillars to pupate, they don't mature and reproduce. 

What makes insects so inconvenient to us is that, as recommended by some psychologists and philosophers, they never think things through logically or discuss them with others (bees are an exception). They have no guide through life beyond their instincts. Having limited perception and no reasoning whatsoever, they are incapable of understanding that they are making themselves nuisances. To get rid of them you have to kill them. Personally, I find some consolation that, in killing nuisance insects, I am helping natural selection encourage the species to develop a higher incidence of instincts that guide them to avoid humans. If we only ever swat the flies that annoy us, we can maintain a healthy population of friendly tachinids and other harmless fly species, without having to put up with houseflies.

Today it may seem that the value of Hemileuca californica is to demonstrate the need to check and correct "the science." Besides the wing color, old authors pointed to other differences between nevadensis and californica. The bodies of both are always furry, but nevadensis, it was easy to see from actual specimens, tapered down toward the tail end, whereas any taper in californica's shape was offset by a tuft of red-orange hair on the tail end. Nevadensis had narrow rings of black and white around the body, while californica's body was dark above its tail tuft. The specimens did look different, but shouldn't the description of their habits have shown that they were at most subspecies variations, more likely variations produced by environmental factors, within one species? How could anyone have been so eager to claim the honor of discovering a new species as to overlook the implications...when animals hybridize easily and produce healthy offspring that inherit and pass on traits from both parents, they belong to one species that can have different looks.

What a contrast between entomology, as a "pure" science studied by people who "only" want to know more about this fascinating world, and some scientific studies that can be "applied" directly to ways of making money. If there were any real commercial profit in clinging to the error, would people who had accepted Hemileuca californica as a distinct species be arguing that those who noticed its crossbreeding with look-alike electra, burnsi, nevadensis, and some others, were deluding themselves for some sort of politically subversive reasons? (Maybe they would tend to feel that blondes should be allowed, if not encouraged, to marry non-blond men?) Would there be efforts to censor discussion of the influence of food plants on Hemileuca color patterns from social media?

This is the fourth Hemileuca post published here--the last one paid for. A few more have been written, and the full series will be thoroughly researched, written, illustrated, and posted at no expense to the student as the articles are funded. They cost $5 each. As with the first four, some posts will be short, noting that named species have been reclassified as subspecies, and others will be long, with lots of pictures. The ones about H. eglanterna and electra are profusely detailed; much more information about the life cycle of californica will be in the article about nevadensis. The pertinent chapters from Tuskes' $400 book are not duplicated in these articles, but they will be consulted. If interest persists they may become a book.