13 September 2026

Earlier this month I saw a caterpillar dangling from a silken thread as he descended from a tree in Schenley Park.

The wind moved him gently to and fro, far and near to me. When he was about to bang into a runner, I reached out and grabbed the thread and it clung to my sleeve. I deposited him in a paved ditch were I could take his picture.

Inchworms, also called spanworms, are the caterpillars of geometer moths (Geometridae), a large family of moths with a global distribution including over 1400 species in North America. Their family name geo+meter means “earth measurer” and refers to the caterpillars who appear to be measuring the earth as they walk.

Because this inchworm came out of a tree, trees are probably his host plant. He might be the caterpillar of a maple spanworm moth (Ennomos magnaria), a common moth in North America whose hosts include all these trees: alder, ash, aspen, linden, birch, elm, hickory, maple and oak. Schenley Park has a lot of hickory and oak so there’s plenty to eat.

Is it a disadvantage that this inchworm is orangish-pink? Well, he probably wasn’t pink while in the tree. Inchworms can change color and then freeze in position to look like a twig as a way to hide from predators. Who are their predators? Warblers! (among other things.)