Usually there is a yellowish stripe on the side of the body though this may be missing. Fall webworm larvae color ranges from light green to very dark brownish-green with a wide, dull, dark longitudinal stripe down the center of the back. Fall webworm has three pairs of prolegs while the spring cankerworm has only two. Both species have one generation per year. Defoliation is often not readily apparent, although trees may appear dead because they are late in leafing out.
Caterpillars begin as hole feeders, then progress to free feeding as they get bigger.
Applying bands of sticky material to the trunks of individual trees to catch the wingless females as they crawl upwards to lay their eggs is an old technique that is worth of more frequent use. This technique has failed in the past because people did not understand that there are two species of cankerworms and they crawl up the trees in different seasons. The fall cankerworms crawls up the tree in October and November and the spring cankerworm in late February and March. In addition, they failed to realize that sticky bands exposed to changing temperatures, blowing dust, etc., lose their stickyness and will not catch the females. Sticky bands should be made from materials that are non-toxic to the tree.