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Eastern tent caterpillars are unsightly, but do not harm trees

The Gwinnett County Extension office has received numerous calls from homeowners about a strange web that has appeared in some of their trees. The webbing is the result of the eastern tent caterpillar, and is more a nuisance than a threat.

The name comes from the ugly tent-like nests they make in the crotches of the host trees. Although heavy infestations can cause serious defoliation, eastern tent caterpillars seldom kill trees. In the landscape, however, nests can be ugly, particularly when exposed by excessive defoliation. Black cherry is their favorite tree, but they can infest numerous other fruit trees and some shade trees.

Often eastern tent caterpillars are confused with the fall webworm. The fall webworm builds its nests at the ends of the branches in autumn, and the loosely woven webs cover the foliage. The webs of the eastern tent caterpillar do not.

Tent caterpillars spend the winter within an egg mass of hundreds of eggs, and begin hatching as the buds begin to open, usually in March. The insects are social; caterpillars from one egg mass stay together and spin a silken tent in a crotch of a tree. They leave their nests to feed on the leaves.

The caterpillars are 1 to 2 inches long, and become a concern as they wander off the tree to find protected shelter in order to undergo pupation. Often they crawl on other types of plants, walkways and storage buildings.

They do not bite people or harm animals, but become a nuisance when large numbers crawl or cluster on building walls, lawns and sidewalks. However, at this phase of their life cycles, no additional feeding or damage is done by the caterpillars. They pupate and emerge as adults, mate and

lay eggs.

People often become alarmed when they see the silken nests. However, the insects pose no threat to the trees. The black cherry is generally considered a weed tree. In other trees they can be ugly, even though they are temporary.

One way to control them is to physically remove the nests out of the tree. Simply scrape the nest off onto the ground and smash the caterpillars or drop them into a pan of soapy water. Larger tents can be pruned out and destroyed. The best time to do this is early morning or late afternoon, when most of the caterpillars are in the tent. Some people have even tried pressure washing them out.

One type of insecticide that can be applied is Dipel, which contains a bacteria harmful to the insects. Treatments also include insecticidal soaps, Orthene, Sevin and some others. The best time to apply an insecticide is when the larvae are small and easy to control, not after they are full-grown and have already done their damage.

But remember, the insects rarely do any permanent damage to the trees. Usually the best course of action is let them finish feeding, and they will go away. The webbing will disappear, as well.

Timothy Daly is an agricultural and natural resource agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010

or timothy.daly@gwinnettcounty.com.