Tent Caterpillars

Robert Bishop 
Frederick County Master Gardener Program

The first noticeable insect pest of spring is the Eastern Tent Caterpillar. Their ugly nests begin to appear early each spring in their favorite hosts, the wild Cherry tree. The nests are web like and usually located in the crotch of tree branches. Their nests can become very large as the season progresses. Many people confuse the tent caterpillar with another pest called a Bagworm. Bagworms are active later in spring, in early June.

Tent caterpillars use their nests as a nighttime refuge until the day begins and they venture out from their safety net to feed on tree leaves. The caterpillars feed on the wild cherry trees first and then move to secondary hosts. Crabapple and Hawthorn trees are the second most favorite preferred hosts. Tent caterpillars also feed on peach, plum, beech, birch, willow, poplar, rose, and witch hazel.

Most damage is minimal and isolated to a particular tree in the landscape. If the insect infestation is very large entire trees can be defoliated. Leaf loss does weaken the tree but because the loss occurs so early in spring there is enough time for the trees to replace them. Years of repeated leaf losses will take its toll on a tree. The continued stress can predispose a tree to attack by other pests.

Control- Remove wild cherry trees from your own and surrounding property whenever possible to reduce the chance of infestation. The safest and often easiest method of control is to simply remove the nests using your hands. Wear gloves to keep your hands clean and smash the caterpillars to kill them. Discard the mangled mash in a plastic trash bag. 

I often hear about people who burn Tent caterpillar nests out of trees with propane torches or gasoline. Excuse me, but this is the most ridiculous pest control option I have ever heard of. Since we now have to put warning labels on our coffee cups I guess I must say, Do not use fire for Tent caterpillar control! There are the obvious dangers to yourself and property, and if the tree does catch fire it will be damaged from the extreme heat.

Biological control can be used in April when the caterpillars are small. Bacillus thuringiensis or B.T. as it is called, is a biological control that is harmless to humans and animals, it is sprayed onto the tree like an insecticide. Sprays applications should target the tree leaves not the nests. B.T. is marketed under a few different names, some are: Thuricide, Dipel, Biotrol, Caterpillar Attack.

In May the caterpillars have grown too large for B.T. to be effective, an insecticide should be used for control. Use horticultural oil, Orthene, or any of the many other labelled insecticides. Apply insecticide spray to the leaves and also try to penetrate the nest with a heavy stream if possible. Follow pesticide label directions always. Tent caterpillars will stop feeding by the end of May and pupate into adult moths. Control methods are only directed towards the caterpillars.

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