Fact Check: "Poisonous Canadian Caterpillar Invades Midwest!"

Every year around the beginning of Autumn I see a story passed around on various social media outlets, especially Facebook. All these stories are titled something to the effect of "Poisonous/Venomous Caterpillar Found in *assorted locations*," and they're all about the little caterpillar of the Hickory Tussock Moth. Even news outlets pick this story up. Sadly, the claims these stories make are pretty much completely wrong. Here's a fact check on the Hickory Tussock Moth.

The Hickory Tussock Moth, Lophocampa caryae, is a species belonging to the Tiger Moths (Tribe Arctiini). The rather dashing adults look like this. The caterpillars, on the other hand, are black and white. These caterpillars are covered in white hairs with a central line of black hairs running down their back.

Reports of the Hickory Tussock Moth courtesy of Butterflies and Moths of North America.

The first thing I want to clarify about this species is their range. Most stories act like these caterpillars are rare in whatever state they're writing about, and that they are coming in from some other location. One of the most hilarious stories I've seen claimed this was a native Canadian species that was "invading Ohio." The Hickory Tussock Moth is actually a really common species throughout New England and the eastern Midwest. Their range also extends north to the very southern portion of the Canadian province of Ottawa. If anything, these aren't a "Canadian species," but an American one that barely extends into Canada. And these caterpillars aren't exactly rare across their range either. I've seen a dozen or so during a single hike before, and that was without trying to look for them. 

But the main thing I want to talk about is their supposed venom/poison, which many stories will say is very dangerous to humans. First, let's clarify what poisonous and venomous means. Poison means a toxin that is ingested (i.e. if you eat it and get sick, it's poisonous). Venom is a toxin that is injected into you via fangs, a stinger, or some other modified part of the body (i.e. if it bites or stings you and you get sick, it's venomous). Unless you plan on eating a caterpillar, the only way it could be dangerous to you is through venom. But is the Hickory Tussock Moth caterpillar venomous?

The short answer is no, the Hickory Tussock Moth caterpillar is not venomous; however, it is a bit more complicated than that. So, let’s start with the basics. Many caterpillar species are covered in hairs called setae. These setae help with sensation, like how a cat’s whiskers do. Many times these setae are harmless (like in the Woolly Bear), but in some species these hairs can break off into an animal’s skin and cause irritation, sort of like a cactus’s spines or bristles. In some other species, like the caterpillars of the Flannel Moths, these setae have been modified into hollow spines, and at the bottom of the spines are venom glands, sort of like a bee’s stinger. The caterpillars with these spines and venom glands can truly be called a venomous caterpillar, but does the Hickory Tussock Moth caterpillar have these? The answer is no. Hickory Tussock Moth caterpillars do not have stinging spines nor venom glands (Hartmann 2009, Kuspis et al. 2001). They do, however, have the irritating setae that I previously mentioned. But, are they really that irritating?

Citations:

Hartmann, T., 2009. Tiger moths and woolly bears. Behavior, ecology and evolution of the Arctiidae.

Kuspis, D.A., Rawlins, J.E. and Krenzelok, E.P., 2001. Human exposures to stinging caterpillar: Lophocampa caryae exposures. The American journal of emergency medicine, 19(5), pp.396-398. Link.

People will often comment on these stories with horror stories about how either they or someone they know touched one of the caterpillars and had a horrible reaction, with some even saying they had to go to the ER. This is not the norm, at all. Some people are, for whatever biological reason, hypo-sensitive to the setae of this species. They can experience pain and bad rashes, yet the average person will not experience this. Let me give you an analogy. Some people are allergic to peanut butter, but the vast majority of people aren’t. Would you say peanut butter is poisonous/dangerous to the average human? No, you wouldn’t. It is the same with the Hickory Tussock Moth caterpillar. A very small percentage of people will have a bad reaction to the setae of this species, but the average person will either have no reaction, or they might itch a bit. To prove a point for science, I pet this Hickory Tussock Moth caterpillar. And not just once — I pet him several times. And what happened? Pretty much nothing. I had a few itchy sensations, but nothing hurt and there was no rash or anything. So much for being a scary and dangerous caterpillar!

Is the Hickory Tussock Moth a species to fear? Not at all! These little guys are just another victim of social media getting animal facts incorrect. It's especially sad to see news organizations (like CBS which claimed this caterpillar wasn't native to the US and that is has venom glands) perpetuating these incorrect "facts." Thanks for reading!