Caterpillars are shaped like a rolled leaf. The rear of the caterpillar extends into a long 'stem'. The head of the caterpillar is large and flat in front, as if mimicking a flat edge of a leaf torn in half. The plump, hairless larva changes colors and pattern as it matures. They can be green with brown spots on the dorsal side (back), or yellow/tan with a larger brown spot draping it. Small eyespots dot the sides of the body. The larval caterpillar feeds on the leaves of popular trees like birch, cottonwood and willows.