Handling Hairy Caterpillars

I’m not the first, nor will I be the last, naturalist to write on this topic. But the subject has gained near-mythic proportions, and I wanted to help set folks’ minds at ease.

This summer it seemed like we had an invasion of hickory tussock moths: small (at the time) fluffy white caterpillars, with some striking contrasting black hairs, were crawling everywhere - on the ground, on trees, across sidewalks, along porch railings. Our campers often squealed and pointed at them, declaring “Don’t touch those! They are poisonous!”

Young hickory tussock moth caterpillar.

This August on one of our Monday Morning Rambles we found a beautiful American Dagger Moth caterpillar, its mustard-yellow hairs offset with several long black tufts. A member of our group picked it up so we could photograph it before it got away from us.

American dagger moth caterpillar.

And every year we marvel at the woolly bear, that iconic black and brown caterpillar of the Isabella Tiger Moth that folklore tells us predicts the duration and severity of the on-coming winter.

Woolly bear - caterpillar of the Isabella tiger moth.

What these, and many other moth caterpillars, have in common are hairy bodies. Some have short hairs, some have short hairs with longer tufts strategically located along the body, and some have quite long “locks.” But are they really and truly dangerous?

The answer is both yes and no, depending on the species and your sensitivity.

For all of these fuzzy larvae, the hairs are a defensive mechanism: a bird is less likely to want to get a mouth full of fuzz, especially if the hairs are irritating.

The key is “urticating hairs” - these are specialized hairs that, when seen under a microscope, possess a barb at the tip, and that break off easily from the caterpillar when the barb grabs onto the skin (or mouth) if a potential predator. The barbs can be irritating (like the tip of a raspberry prickle that you discover in your thumb two days after you brushed against the raspberry), making your skin itch or feel like it is burning a bit, but otherwise they are harmless.

However, some species’ urticating hairs are connected to venom sacs, and under a microscope their tips are more like hyperdermic needles (similar to the hairs on stinging nettles). When a potential predator brushes/grabs these hairs, a dose of venom is delivered, which can result in anything from itchy skin to sever blisters and swelling, depending a) on the species of caterpillar, and b) on the sensitivity of the “victim” to the poison. Just like some people react to poison ivy and others do not, a person’s reaction to the venom of these caterpillars will be on a spectrum.

Now, to be fair, most animals that are “dangerous” give plenty of warning ahead of time to leave them alone. Monarch butterflies are bright orange and black - their color is a warning to birds not to eat them because they taste bad; skunks are boldly patterned in black and white, a warning to leave them alone; rattlesnakes shake their tails to make their presence known and hopefully drive away potential predators. These caterpillars are not so different: many have striking colors or bold patterns (such as strategically placed long hairs) that warn us to stay away. It’s hardly their fault if we ignore their signals!

I have handled many a fuzzy caterpillar in my day, and I have never had any adverse reaction from any of them. Does this mean I am immune? I doubt it. I think it is more likely that I am gentle when I handle them, and I tend to let them crawl onto me, rather than grabbing them from above.

So, be aware that some caterpillars can be dangerous to handle. As with most wildlife, we should admire them from a safe distance. And if you must handle a fuzzy caterpillar, know that woolly bears are considered, for the most part, safe to handle.