In Praise of Fuzzy Caterpillars

The last time I strolled along a trail at the Arbore­tum, I spot­ted anoth­er fall wan­der­er — a small black-and-white fuzzy cater­pil­lar. Unlike me, he had a clear pur­pose in his trav­els — he was seek­ing a cozy place to spend the win­ter. Once he found a shel­tered spot — under a log, or in a crevice of bark — he would shed all those fuzzy hairs and use them to craft a snug cocoon. This lit­tle fel­low was a hick­o­ry tus­sock moth. These moths munch on hick­o­ry leaves and the leaves of oth­er plants, but don’t cause a lot of dam­age to trees.

I’ve always had a soft spot for cater­pil­lars, and when I was a kid, I would have picked him up and maybe put him on a stick and watched him crawl along, just for fun. Seems as though noth­ing could be more harm­less than a fuzzy cater­pil­lar. But I’ve been see­ing these lit­tle guys all over the media late­ly— on Face­book, on Twit­ter, and even on the evening news and in the local papers. And the cater­pil­lars are always described with words like ​“lethal,” ​“dan­ger­ous,” and ​“ter­ri­fy­ing.” And the scari­est word of all: ​“ven­omous.” Was I real­ly risk­ing death when I picked up a tus­sock moth cater­pil­lar in my youth? Are they real­ly a life-threat­en­ing menace? 

In a word, no. Tus­sock moth cater­pil­lars don’t bite or sting. They’re not ven­omous in the sense that a cobra or a scor­pi­on is, with fangs or stingers to inject dead­ly poi­sons into humans. The prob­lem is that some of the cater­pil­lar’s bris­tles are what are called urticat­ing hairs. Like the spines of a net­tle, these hairs can cause a rash on sen­si­tive peo­ple, but it’s usu­al­ly a pret­ty mild irri­ta­tion. The skin on the palm of your hand is fair­ly thick, so you’re unlike­ly to have any prob­lem from pick­ing up a cater­pil­lar. But if the cater­pil­lar brush­es against an area with sen­si­tive skin, like your stom­ach or your neck, an itchy reac­tion is more like­ly. So don’t cud­dle them against your cheek, don’t put the bris­tles in your eye. Don’t lick them. (Peo­ple have done these things.)

It’s not that they’re try­ing to irri­tate us. It’s the way the cater­pil­lar sur­vives. When a blue jay grabs a cater­pil­lar for lunch, the cater­pil­lar thrash­es back and forth, thrust­ing the urticat­ing hairs into the bird’s face. The blue jay quick­ly learns to avoid white, fuzzy food. Lat­er, when the cater­pil­lar pupates, it uses the urticat­ing hairs to make its own cocoon. The soft lar­va inside the cocoon is defense­less, but the cocoon would be an itchy mouth­ful for a hun­gry predator. 

So tus­sock moth cater­pil­lars are cer­tain­ly not lethal. The warn­ings about ​“ven­omous” and ​“poi­so­nous” are mis­lead­ing — ​“pos­si­bly aller­genic” is a bet­ter term. They will not inject ven­om into you and kill you. 

The good thing about these lit­tle fel­lows is that they’re a native species. They’ve been here for mil­len­nia. They’re yet anoth­er strand in the immense and inter­twined food web of the east­ern for­est. In all their life stages — egg, lar­va, pupa, adult — there is some­thing that eats them, some­thing that needs them for nutri­tion. Many wood­land birds, like chick­adees and nuthatch­es, are espe­cial­ly fond of insect eggs. The tus­sock moths belong here. 

Know­ing all this, try to resist the temp­ta­tion to squish them or spray them. They grow up into harm­less but absolute­ly gor­geous moths. Think of the beau­ty we’d miss.