Tent Caterpillar Or Fall Webworm?

Depending upon what time of year it is, you may look up in our trees and see a mysterious and ugly mass of webbing in your trees. The reason what season it is matters because there are actually two damaging pests that can infest your trees and they appear at different times of the year. Tent Caterpillars appear in the spring and Fall Webworms appear in the, you guessed it, fall.

How you treat them is very similar, but there are some differences in their habits and characteristics that are important to understand.

Tent Caterpillars (Malacosoma americanum)

Tent Caterpillar

Tent Caterpillars hatch from eggs in early March and their tents will soon appear in the crotches of trees. Their favorite hosts are Cherries, Crabapples, Hawthorn, Maple, Cherry, Peach, Pear and Plum.

The caterpillars stay in the nest during the heat of the day or during rain, and come out to feed on leaves in the morning, evenings or at night. If there is enough of a population, they can quickly defoliate a tree.  the tree will usually recover and put out a new crop of leaves. In the landscape, however, nests can become an eyesore, particularly when exposed by excessive defoliation.

Tent Caterpillar Nest

The larvae are hairy caterpillars, black with a white stripe down the back, brown and yellow lines along the sides, and a row of oval blue spots on the sides. In four to six weeks after hatching, the caterpillar will build a cocoon and soon become a moth.

How To Treat For Tent Caterpillars

Early control is important. Removal and destruction of nests is probably the most effective control.

Young caterpillars can be killed by applying an insecticide containing Bacillus thuringiensis varkurstaki, a naturally-occurring soil bacterium that produces poisons which cause disease in insects.

Pesticides are generally not effective against mature larvae.

Fall Webworm (Hyphantria cunea)

Fall Webworm Caterpillar

Fall Webworms webs will start appearing in mid to late summer.

Fall Webworms can be up to one inch long. They come in two color forms. Those with black heads are yellowish white while those with red heads are brown. Fall webworms are covered with long, soft gray hairs.

Fall Webworms will feed on more than 100 types of trees but they prefer trees like Pecans, Black Walnut, Mulberry, Elm, Sweetgum, Willow, Apple, Ash and Oak.

The caterpillars form fine silken webs on the ends of the branches. They will enlarge the webs if they need more leaves. They feed on the leaves in these webs for a couple of weeks before they leave the trees to become pupae. These pupae eventually turn into a white moth. This moth may have black spots. This moth can fly away to lay eggs on trees to start another generation of webworms.

Fall Webworm Nest

How To Treat For Fall Webworms

Since most trees will not die from caterpillar attack, it is not generally recommend spraying. If you want to control the caterpillars by spraying, you must treat the entire tree – perhaps more than once. You will usually need to hire a tree service to do this.

If you do decide to spray; use insecticidal soap, horticultural oils or Bacillus thuringiensis to kill small caterpillars. These insecticides are less likely to kill the natural predators that keep the levels of these webworms low.

Like the Tent Caterpillar, removal and destruction of nests is probably the most effective control.

CAUTION! Always follow label instructions when using pesticides. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.

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