Tent caterpillars are pests known throughout the Unites States for their silken tent that appears in trees. The tent caterpillar is second to the gypsy moth as a major tree pest. Proper identification of the caterpillar and the tree it is in will determine your best course of insect management. Although it is often assumed tent caterpillars attack evergreens, this is rarely the case. Other insects similar to the tent caterpillar do.
According to Cornell University, both the forest tent and eastern tent caterpillar rarely feed on evergreen trees. The fall webworm is also known to avoid evergreens. Gypsy moths are the most likely insect within this family to feed upon evergreen trees.
Several insects commonly mistaken for the tent caterpillar are found on evergreens.
The fall webworm lives throughout the United States and Canada. They grow later in the season than the other tent caterpillar varieties. They build similar tents to the other caterpillars and are often mistaken for tent caterpillars. Fall webworms build their nests at the end of the tree branch as opposed to sheltered inside the tree.
The bagworm is a caterpillar that forms a small bag in evergreen trees. The bag of the bagworm is 1 1/2 to 2 1/2 inches long. Adult males have wings while the females stay in the bag as a larvae. The bagworm feeds off the evergreen, consuming buds. The silken bag may damage branches as they grow.
Eastern Tent Caterpillar
The eastern tent caterpillar occurs in large numbers every 10 years, says the University of Kentucky Extension. The eastern tent caterpillar prefers wild cherry, apple and crabapple trees, but will also feed on ash, birch, willow, oak and poplar.
The eastern tent caterpillar spends the winter in egg form. Caterpillars begin making a tent once the eggs hatch. The tent becomes larger as the larvae of the insect grows. The caterpillar will leave the tent for food but always returns. Larvae are black with a white stripe, and on its side are two yellowish lines around blue marks.
Forest Tent Caterpillars
Forest tent caterpillars are similar to their eastern counterparts. They fed from the top of the tree as new buds form, moving down into their tent once finished. The larvae will concentrate on one branch at a time. The forest tent caterpillars have a key-shaped mark on their back that differentiates them from eastern tent caterpillars. The forest tent caterpillars prefer sweetgum, oak, birch, ash, maple, elm and basswood trees, and will not likely attack evergreen trees.
Both the eastern and forest tent caterpillar eat the leaves of the trees they infest. Leaf damage begins in the early spring. A tree will survive the first two to three years of defoliation before the tree's growth and vigor is affected by the damage. The bags of the caterpillars will not decay, binding up branches, which may cause wet conditions that encourages the growth of fungus.