18 September 2021

This gorgeous yellow caterpillar is an American dagger moth (Acronicta americana), a 2-inch long member of the owlet family Noctuidae. As a caterpillar he attracts attention.

As a moth he does not.

The difference is a matter of self defense. The adult American dagger moth is probably good to eat so he does his best to hide.

The caterpillar is conspicuous because he has a toxin in his black bristles that cause a stinging sensation when the bristles break off and embed in skin. Like many poisonous animals he’s using aposematic coloration and behavior to simultaneously attract attention and warn off predators, “Look. Don’t eat me.” Other examples include poison frogs, monarch butterflies and skunks.

However, this caterpillar is not invincible like the hickory tussock moth. If you know what you’re doing it’s possible to flatten the black bristles and touch the dagger moth caterpillar as Rebekah D. Wallace does, below, to show the spiracles under the caterpillar’s “fur.”

No thanks. I’ll look but not touch.

(photos by Kate St. John, Wikimedia Commons, and Rebekah D. Wallace, University of Georgia via bugwood.org; click on the captions to see the originals)