Top Photo: Polygonia interrogationis on Ulmus.
The caterpillars in these photos are question marks (Polygonia interrogationis). They’re butterfly caterpillars. Looking at the photos you may think they’re named for the shape they sometimes assume when disturbed. Not so.
They are, in fact, named after the punctuation mark (?) but not because of the way the caterpillars scrunch up when hassled. No, question marks are named for markings on the underside of the adult butterfly’s hindwings which are roughly the shape of a question mark.
Question mark butterflies lay eggs on elms, hackberry, hops or nettles. The caterpillars pictured are on a young elm in Gateway Park here on campus. The adults lay small chains of eggs on their chosen plant. If you find one caterpillar you may find more. Though not all visible here, there were at least eight caterpillars on the tree below.
The spines on the caterpillar, though intimidating, are harmless.
Unlike many species of butterflies, question marks overwinter as adults and may be seen flying through the woods on warm winter days. A couple of sunny days in the fifties in December, January, or even February should get a few out flying. They shelter in crevices, tree cavities, or other secure places in the woodland.
Keep an eye out for an erratic flying orange butterfly this winter during a warm spell. It’s more than likely a question mark, or was that a comma?
These caterpillars were first brought to my attention by Ranger Robert who, when not photographing the red wolves, can be seen ranging the museum grounds, inside and out.