Caterpillars Most of the leaf-chewing larvae of butterflies and moths can be grouped together and referred to as caterpillars. They are soft-bodied except for a hard head capsule and have three pairs of thoracic legs and two to four pairs of fleshy abdominal prolegs. Caterpillars come in various sizes, shapes and colors. They may chew holes in leaves or chew inward from the leaf edge.
Some caterpillars are hairy, while others are smooth-bodied and mimic twigs.
Most have a protective coloration that helps them blend into the background of twigs and leaves. Several species of caterpillars can feed on shade trees and ornamentals in the north central states, but few commonly cause significant levels of defoliation. Most caterpillars occur chronically at non-damaging levels and are damaging only rarely. Problems one season often are not followed by problems the next year. Because the great majority of feeding by a caterpillar is done during the latest larval stages, defoliation may appear to occur very suddenly.