TENT CATERPILLAR, EASTERN – Also called the apple tree tent caterpillar. The larvae of certain species of moth common throughout the U. S., often completely defoliating in spring unsprayed orchards and sometimes ornamental trees and shrubs, and filling wild cherry, apple and other trees along roadsides with large unsightly nests. The winter is passed in the egg stage, gray or dark-brown, shiny egg masses about 1/2 in. long encircling small twigs as though a bit of gum had been wrapped around them and varnished. The eggs hatch just as the apple leaves unfold and the tiny worms at once attack them, at the same time forming a colony in the nearest branch fork and building a weblike nest for protection at night and in wet weather. As the caterpillars crawl out to feed, they leave a silken trail behind which may connect several nests over the tree. In about a month the caterpillars, fullgrown, and 2 in. long, black, with bluish markings and a white stripe down the back, leave the nests, crawl along the ground, fences, buildings, etc., and pupate in dirty whitish dusty cocoons fastened on tree trunks, under bark or shingles or on any sort of trash. The small heavy-bodied moths, appearing in early summer, have short, reddish-brown wings with white bands. There is but one brood a year and “tents” seen in midsummer or later are caused not by this pest but by the fall web-worm, which see.
A regular spray program will control the tent caterpillar in orchards. In gardens and home grounds the nests may be removed by burning with a torch – if the work is done carefully, so as not to injure the tree. A better plan is to wipe them out of the crotches with rags moistened with kerosene, gasoline or some full strength contact spray. The sooner this is done, the easier, pleasanter and more effective it is. But the best means of control is by pruning off and burning the twigs carrying egg masses. Do this any time while the leaves are off the trees, when the masses can be easily seen against the sky. Birds and other insects (including parasites) are natural enemies of the tent caterpillar and a natural balance is gradually established so that after the pest has been abundant for four or five years it usually disappears for the same length of time.
The related forest tent caterpillar is a pest of woodlands but may defoliate shade trees such as poplar, maple and oak. The blue-headed caterpillar has a line of silvery, diamond-shaped spots down the middle of the back. Again the winter stage is the egg, 1/4-in, long light-brown masses being laid on the twigs of host plants. No web is formed so control consists of spraying with Malathion in spring, as the egg masses are rarely within reach.
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