Most caterpillars are harmless, a few dangerous, some just scary

StoryImage( ‘/Images/Story//Auto-img-111765473314792.jpg’, ‘Photo courtesy of’, ‘This fierce-looking hickory horned caterpillar is the immature stage of the regal moth. Full-grown larvae can reach lengths of 4 to 5 inches. On the thoracic segments behind the head are long, stout, orange and black spines or “horns.” Host plants include hickory, walnut, butternut, sumac, persimmon, sweetgum, ash and sycamore.’);

Almost everyone knows that a caterpillar is the larval or immature stage of a butterfly or a moth. This great order of insects known as the Lepidoptera (meaning scaly wings) is represented in the United States and Canada by more than 11,000 different species. Caterpillars are of considerable economic importance as many are serious pests of cultivated plants, trees, fabrics, and stored food products. A few are of medical importance and can pack a terrific wallop if they happen to sting you. On the other side of the coin, many adult butterflies and moths are beautiful and sought after by collectors or form the basis of art and design.

Butterflies and moths go through a complex series of developmental stages called complete metamorphosis (many shapes) where the immature stages in no way resemble the adults. A butterfly egg hatches into a larva or caterpillar whose main purpose in life is to eat as much as it can. After the caterpillar has fattened itself up, it usually spins a silken cocoon about its body and enters the pupal or resting stage. During this stage, the pupa is immobile and does not feed while drastic internal changes are taking place as it miraculously transforms itself into an adult butterfly or moth.

There are about as many different caterpillars as there are different butterflies and moths, and the vast majority of them are not dangerous to humans. There are, however, three in the United States that possess sharp spines or hairs connected to venom glands. These are the saddleback, Io, and the puss caterpillars, and contact with any of them results in a painful experience.

The Io is a green animal with a red stripe along each side. The hairs that cause the damage are also green in color. The saddleback is also mostly green with dark areas at each end of the body—hence the name saddleback.

The puss caterpillar is by far the worst of the three. It is a small creature about an inch in length with a coloration that varies from gray to yellowish, to brown. Its body is densely covered with fine, soft hairs. Apparently, someone long ago thought it resembled a very small cat and stuck it with the name of puss caterpillar. It is not very active, but, unfortunately, it is just the type of beast inquisitive children like to pick up, much to their regret.

Hidden under the silky hairs are sharp spines laden with poison that is apt to have deleterious effects if injected into the skin. In Texas, where I grew up, puss caterpillars are commonly called Mexican asps. I can vouch for the fact that the sting of a puss caterpillar can be a painful and sometimes debilitating experience. While I was wearing short pants and engaged in some childhood activity under a hackberry tree, two of these monsters crawled up my thigh and stung me when my body touched them. Immediately I felt as if I had sat on red-hot needles, and an unbearable ache soon developed in my groin area. It was several hours before the pain and discomfort abated, and I felt normal again. In some individuals, the effect of a puss caterpillar sting may persist for days. I always avoided that hackberry tree after that, and on a visit to my old homestead some years ago, I was delighted to note that the tree had been removed from the area.

Some caterpillars are ferocious-looking creatures but are completely harmless. One of these is the hickory horned devil that we occasionally encounter in the Rock River Valley, though it is more common in central and southern Illinois. It is the caterpillar that develops into the regal moth that is sometimes called the royal walnut moth. The devil’s favorite habitats in our area are hickory and walnut trees where they spend their larval lives munching on leaves. They are not commonly seen, as the only time they descend to the ground is to burrow into the soil and transform into pupae.

The hickory horned devil is a very large creature, being up to 6 inches in length when fully grown. Two large, menacing, spine-like horns adorn the head region, and the rest of the body is covered with shorter, spike-like spines. The devil gives a dangerous and frightening appearance, but it is completely harmless. This overall ferocious façade probably protects it to some extent from would-be predators.

If you happen upon a hickory horned devil, do not destroy it, as populations of the exotic regal moth are declining due to the loss of forests and the indiscriminate use of pesticides.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

From the June 1-7, 2005, issue

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