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Fall webworms are caterpillars that form colonies inside spiderweb-like sacks. These sacks can be feet across and are generally found on the ends of branches. The caterpillars appear on trees in the fall and defoliate the branches inside of their sacks. This is an unsightly pest but is generally not harmful to the long-term health of their hosts since trees will soon lose their leaves in the autumn anyway. These caterpillars feed on many tree species, their favorite being black walnut, and hickory. In addition, they are often found on elms, ashes, maples, apples, and other fruit trees. While the caterpillars are black or brown, the adult moths are all white or white with black spots.
Fall webworms are most damaging to young trees. In this case, their colonies can often be reached with a branch and manually removed. Colonies can be dunked in soapy water to kill them or burned. Larger trees rarely have any permanent damage, so the worms are best left alone, especially if it is unsafe to remove them. Spraying is generally ineffective unless the web is broken open; then, a product containing spinosad, such as Bonide’s “Captain Jack’s Deadbug Brew,” can be used.