Preventing Tent Caterpillars

Hate those silky little web tents clinging to your favorite tree? Read to learn how to prevent or eliminate them.

Tent caterpillar (or more correctly, caterpillar) is a term used to include several types of caterpillars, specifically the eastern tent caterpillar and the forest tent caterpillar, both of which create webs of silk on fruit and forest trees. Both can be easily misidentified as gypsy moth larvae.

East of the Rocky Mountains and Canada are the habitats of the more familiar of the two, the eastern tent caterpillar, and large nests can be observed along roadside trees. Smaller nests will be found on fences and ornamental trees. Large gatherings of eastern tent caterpillars are seldom found in ornamental trees. Covered with yellow hairs, they sport a white stripe down their back and are black with blue and white markings.

Favorite trees of these larvae include apple, cherry, crabapple, peach, and plum. Less often, they'll nest in ash, birch, hawthorns, maple, oak, poplar, and willow. Total defoliation of small trees can occur when one or two colonies are present. This occurs early in the season, so the trees will be able to grow new leaves the same year, although the labor will cost them quite a bit in energy.

Found on a variety of deciduous trees (trees that lose their leaves seasonally), forest tent caterpillars behave similarly to the eastern tent caterpillars. Their favorite trees are maple, and the larvae can be found throughout the forested parts of the United States and in northern Mexico and southern Canada. These creatures build a silken carpet to be used as a home base rather than a tent. Where the eastern tent caterpillar has the continuous stripe on its back, the forest tent caterpillar has white dots instead.

Tent caterpillars search for a new source of food by migrating en masse, and thousands of them can be observed traveling together over ground surfaces such as roads, driveways, and sidewalks. Eggs of the tent caterpillars are placed in cylindrical bands on the twigs of trees in midsummer, and they don't hatch until the following spring. Larvae instantly head for a fork in the tree, where they build a large silken tent, or a carpet, as in the case of the forest tent caterpillars. Each morning, the larvae leave the nest (either a tent or a carpet) and feed, returning to the nest in the evening. This pattern repeats itself every day until early summer, when the caterpillars are grown.

Three methods have been employed in an attempt to control or prevent tent caterpillars from assuming residence in their trees. They are:

1. Insecticide Sprays - Direct sprays of most contact and stomach insecticides to the nest and plant foliage afford rapid control. Late morning is the best time of day for this, as the larvae gather on the surface of the tent to bask in the sun.

2. Bacillus thuringiensis (Bt) - Although several predators and parasites attack tent caterpillars, they do not appear in sufficient numbers in some years to be effective. This type of control is designed to control caterpillars of any kind, but it will also eliminate tent caterpillars.

3. DIY (Do It Yourself) -Egg masses will be present and clearly visible after the leaves drop in the fall. They can be cut off for disposal. If you miss a few masses, you'll have lots of time in the spring to remove them. Pull the nest onto the ground, and crush the caterpillars either early in the morning or the late afternoon, which is when most of the caterpillars will be in the tent. Be sure to use gloves since some people find the caterpillar hairs irritating.

Considering that large colonies in the thousands often migrate in search of new food sources, you can't really avoid tent caterpillars completely without the use of insecticides, and you need to consider carefully whether you think they do enough damage to warrant that kind of strong treatment. Defoliation occurs early enough that the leaves are replaced, and it's easy enough to destroy the webs with a strong spray from a garden hose. This will eliminate the unsightliness of the tents and carpets. And, as stated earlier, large colonies don't usually attack ornamental trees.

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