Nature Walk: The toothbrush caterpillars

A hickory tussock caterpillar on our back shed wall. (Photos by Anita Barbour)

The past few weeks we’ve been noticing a lot of what we call “toothbrush caterpillars.” What they have in common are tufts along their backs that give them the look of toothbrushes with their working ends facing upwards. Others are not so brushlike, but are included here for general resemblance in bristliness. There is only one bristly roly-poly (rounded in cross-section) species that we found in the yard, the caterpillar of the giant leopard moth (Hypercompe scribonia). In general, caterpillars with bristles or hairs are not threatening to most people. An exception among the caterpillars we found is that of the hickory tussock moth (Lophocampa caryae), whose hairs cause a painful rash. Some species groups such as buck moths (genus Hemileuca), which are not found around here, have caterpillars that sport spines that itch like nettles (hence the descriptive term “urticating,” derived from Urticacae, the botanical name for the nettle family).

As food for birds, small mammals, wasps and other predators, a caterpillar is juicy and protein-packed. Bristles, especially toxic ones, can protect a caterpillar by making it unappetizing or inedible to animals (especially birds and mammals).


A gray and yellow fall webworm occupies a leaf of honeysuckle.

Shown here, resting on a leaf of honeysuckle, is a fall webworm (Hyphantria cunea). These caterpillars are variable in color, ranging from pale yellow to charcoal, according to Caterpillars of Eastern North America by David L. Wagner. Wagner writes that this species feeds on over 400 kinds of woody plants, as well as on herbaceous plants. Photographed on our front porch steps is the hickory tussock caterpillar, whose favorite foods besides hickory are pecan and walnut leaves. Others are oak, ash and willow, but the caterpillars may be found on almost any woody species.

Native to North America, the fall webworm is one of the few insect pests from this continent to have been introduced into other countries all around the globe, according to Wikipedia’s website (https://en.wikipedia.or/wiki/Fall_webworm). It is now found from France to the Caspian Sea, in central Asia and Russia, even in China and Japan.

The high number of caterpillars dead or dying this late summer (especially fall webworms) is almost certainly attributable to the stiflingly hot and humid weather we had, and the stretches of abundant rain. We’ve seen shriveled, almost denuded caterpillars hanging from fences, branches, even boxes on the porch.

Many hairy caterpillars are in the tiger moth and wasp moth groups, but other bristlies may also be found among the butterflies such as fritillaries and checkerspots. You may want to look for these interesting toothbrush caterpillars in your own neighborhood. There are other insects that resemble caterpillars: ladybug larvae, other beetle grubs, centipedes, wasp larvae. Most caterpillars have one pair of clasping, grasping hind legs, and three pairs of tiny, hook-like grasping legs under the “chin” and mouth, with its paired, sideways nibbling jaws. Most caterpillars have four pairs of Velcro-like clasping legs in mid-body, which cling to twigs and leaf stems. Observe the hairy caterpillars without touching them, though. We do not have lethal ones here in New York, like the South American caterpillar said to have caused more than 500 deaths. But some can be quite irritating, and worse, can cause severe allergic reactions in some people.

1) This isn’t a hairy caterpillar.  It’s the drooping spike of a giant foxtail grass, growing next to a Kingston wetland. 2) This yellow fall webworm (a caterpillar, not a worm) rests on a wire fence. 3) The black and white hickory tussock moth caterpillar, showing its toothbrush-like back.  This one was on our porch step. 4) Moth caterpillar (Datana angusii) strolling along our porch step. 5) Moth caterpillar (Datana angusii) in a defensive posture.