Tree Insects - Fall Web Worms
The large silk webs enclosing tips of branches are sure signs of fall webworms. The caterpillars remain inside the webbing, and if food runs out new foliage is encased.
The caterpillars are covered with long white to yellowish tan hairs. Two races of fall webworms occur in North America, the blackheaded and redheaded races. The blackheaded race has caterpillars which are light greenish-yellow to pale yellow with two rows of distinct black tubercles.
These caterpillars are more unsightly than damaging to the trees. They feed just prior to leaf drop in the Fall causing little damage to the biomass of the host plant. Border trees do not normally warrant control. Specimen or feature trees may. Tents can be cut out and burned or you can control with a foliar contact insecticide application.
The redheaded race is more tan in color with orange to reddish tubercles. The caterpillars make distinct jerking movements in unison if the nest is disturbed. The adults are about one inch long and range from pure white to white with a few black spots.
This pest overwinters in the pupal stage. Pupae are usually in the ground but can be located in old nest remains, under loose bark and in leaf litter. The adults emerge from late May into July. The eggs are usually deposited in a single (blackheaded race) or double (redheaded race) layer of several hundred eggs on the undersurface of leaves. The mass is lightly covered with scales from the female's abdomen. The eggs hatch in about a week and the small mass of caterpillars web over single leaves and feed by skeletonizing. As the caterpillars grow, they web over additional leaves and finally are able to eat the entire leaf. The larvae mature in about six weeks, at which time they drop to the ground to pupate.