Saturday, October 12, 2013

Caterpillars of the Fuzzy Variety

We have all seen the black-orange-black "woolly bear" caterpillars before, but there are a whole slew of other hairy caterpillars out there. I recently came across a few at The Ridges in Athens, Ohio, so let's take a look!

Banded Tussock Moth caterpillar
First, let's start with a commonly encountered species. This gray, tufted individual is a caterpillar of the Banded Tussock Moth, Halysidota tessellaris. What exactly are the fuzzy hairs covering his body? These are something called "setae," which are hair-like bristles. A seta (plural setae) is a stiff bristle which originally evolved to aid in sensation, sort of like how a cat uses whiskers. However, in many species these setae have been modified for defensive purposes in a manner analogous to the spines and bristles which a cactus uses for defense.

Banded Tussock Moth Caterpillar
Banded Tussock Moth caterpillars can come in a variety of color morphs. They can be gray, as you saw in the previous photo, but they can also be yellow, like the individual in the photo above. This is a very abundant species in the forests of the eastern US, and an observant hiker can often find several during a walk through the woods from July to October in a good year. 

Salt Marsh Moth caterpillar
This fuzzy individual is a Salt Marsh Moth caterpillar, Estigmene acrea. Don't let the name full you; these guys are found all throughout North America (save Alaska and the Yukon), and not only in salt marshes. The caterpillars feed on a really wide variety of plants, and many times will be seen wandering around on the ground in search for new food sources.

Milkweed Tussock Moth caterpillar
While many caterpillars will feed on a variety of plant species, some specialize in only one or two specific groups of plants. An example of this would be the caterpillar of the Milkweed Tussock Moth, Euchaetes egle. This species feeds primarily on various milkweed species, but will also feed to a lesser extent on dogbane (Apocynum spp.). Like the Monarch, the Milkweed Tussock Moth has evolved an adaptation to withstand the toxins in milkweed plants (and also dogbane species), and they can consequently exploit a food source that many species cannot use. And, again like the Monarch, the Milkweed Tussock Moth is able to sequester a modified version of the toxin and use it as a personal defense. Although the Milkweed Tussock Moth and Monarch derive different toxic compounds (cardiac glycosides and cardenolide aglycones, respectively), the results are the same: a caterpillar or adult that is unpalatable to any would-be predators.

Hickory Tussock Moth caterpillar
Next, I want to talk a bit about this infamous caterpillar. This is the Hickory Tussock Moth, Lophocampa caryae. It's infamy stems from the numerous news and social media stories passed around every year about its supposed "dangerous venom." But here's the thing: it is not venomous. This species is actually pretty harmless, but misinformed stories sadly continue to be shared via Facebook and even national news outlets. If you want to learn more, check out my post dedicated entirely to the Hickory Tussock Moth caterpillar, which you can read: right here!

Woolly Bear
And of course, what post on fuzzy caterpillars wouldn't be complete without the "woolly bear" caterpillar everyone knows and adores? This commonly seen caterpillar is the caterpillar of the Isabella Tiger Moth, Pyrrharctia isabella. And you know what? These caterpillars are amazing. They hatch from eggs in the fall and overwinter as caterpillars. And when they overwinter, they can withstand freezing solid! Their heart stops, then their gut freezes, then their blood, and then the rest of its body. This would kill most other organisms, but not the Woolly Bear. They simply thaw out in the spring, pupate in a cocoon, and then emerge as adults. Depending on how short the growing season is, the Woolly Bear can sometimes take several years to reach the pupation stage. Some individuals have lived through 14 winters before pupating!

What about the wive's tale which claims the amount of orange/red on the Woolly Bear indicates how harsh the winter will be? It's just that—a wive's tale. Even within a single batch of eggs, each caterpillar can vary in the ratio of black to orange. The central band also grows with age, and it has nothing to do with the weather.

Adult Woolly Bear
An adult Woolly Bear, known as an Isabella Tiger Moth.
Pyrrharctia isabella is an example of a Lepidopteran (butterflies and moths) species having two common names—one common name for the caterpillar stage, and another for the adult. In this case, the caterpillar is known commonly as the Woolly Bear, but the adult is called the Isabella Tiger Moth. Another example of this double-naming would be Citheronia regalis, which is called the Hickory Horned Devil (read about them here) as a caterpillar and a Regal Moth (or Royal Walnut Moth) as an adult.

The species covered in this post are only a fraction of the fuzzy caterpillars out there—there are dozens and dozens of other species. If you're really interested in identifying caterpillars of all kinds, I highly recommend the Princeton Field Guide to Caterpillars of North America. It is a wonderful guide to caterpillars if you live in the Eastern US!


  1. My 7 year old son wanted to know more about the caterpillars in ohio.. We really enjoyed reading this page.. He knows now that the Woolly Bear is harmless compared to the white caterpillars we have in the yard.. Thanks..

    1. That's great to hear! There's a whole world of awesome caterpillars out there, and I hope your son continues to explore their world as he grows up!