The fall webworm is a native caterpillar that constructs large, unsightly webs on the outer ends of tree branches. The silk webs are formed around the shoots and leaves of shade trees when the caterpillars are young. As the caterpillars feed and grow, the web is expanded to surrounding leaves and becomes larger and larger. Skins cast off by the caterpillars when they molt, fecal pellets and dead leaves accumulate in the web, giving it a messy appearance.

Fall webworms have black or red heads and pale green to yellow bodies. Long gray or white hairs grow from two rows of bumps on the caterpillar's back. When fully developed, the caterpillars are about an inch long.

Although the webs are unsightly, defoliation by fall webworms seldom causes any serious harm to the tree. Since the insect is a native species, it has several natural enemies, including egg parasites and caterpillar parasites. When infestation occurs on ornamental or landscape trees, other control measures may be needed. If webs are accessible, branches can be pruned out, webs and caterpillars can be burned, buried, or destroyed by soaking in a bucket of soapy water for a few days.

Maintaining tree health is important in helping your tree recover from defoliation and other stresses. Water trees during dry periods, and avoid wounding trees or compacting soil within the drip line.

more info: http://www.ag.ohio-state.edu/~ohioline/hyg-fact/2000/2026.html