In the Garden:
New England
June, 2004
Regional Report

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I can appreciate the beauty of this Eastern tent caterpillar, but in large numbers it can be very destructive.

Eastern Tent Caterpillars on the Rise

While New England has been spared the worst of the locust invasion this spring, we face other pests that also have cyclical population explosions. This year, eastern tent caterpillars have me climbing the walls, or, rather, the trees.

Tent Cities
In the past we've had the occasional caterpillar tent in our trees, but last year a favorite crabapple tree was damaged from their feeding and this year the caterpillars are everywhere -- lurking in the grass, climbing up the siding of the house, crawling on tree trunks ... everywhere. I watched a blue jay pecking away at something in our pin cherry tree, and when I looked closer I was delighted to see he was opening a web of tent caterpillars for lunch.

The white webs in the crotches of tree branches might be the first visible signs that you have these leaf-eating insects in your yard, but the larvae actually spend the winter close by. If you look closely in autumn after the leaves fall, you can see their black, shiny, egg masses on twigs and branches of their host trees: apple, crabapple, plum, peach, cherry; and to a lesser extent: ash, birch, willow, maple, oak, and poplar. If you've had problems in the past, you may be able to eliminate them by checking these trees and destroying the eggs.

The larvae hatch about the same time their host plants leaf out in spring, feeding on leaves while taking shelter in the protective tents. These black caterpillars have a white stripe along their length and a series of blue dots along each side of the stripe. They crawl to young leaves to feed, usually in the morning or early afternoon. Then they return to their tents. The larvae lay down silk trails as they move, and these serve as roadways for other larvae to follow.

Tent caterpillars have an uncanny way of making their tents so high in trees that you can't reach them easily, but it's worth finding a ladder and a long pole because a couple of large webs full of caterpillars can defoliate a small tree. While most healthy trees can withstand some loss of leaves and will send out new ones, if the damage is severe the tree might not recover.

So after the blue jay had its fill, I poked into the webs, twirled them around a broom handle, knocked them to the driveway, and stepped on the caterpillars. You also can drop them into a can of soapy water.

After about four to six weeks of feeding, the caterpillars are about 2 inches long. Then they start their travels in search of a place to pupate, and that's when we encounter them underfoot and overhead.

Fortunately there's only one generation per year. The caterpillars spin their silvery cocoons (check the sides of buildings and fences), and reddish brown moths with two white stripes on each wing emerge in July to mate, lay eggs, and die.

A spray of Bt (a biological control) can be effective when the caterpillars are small, but sprays don't easily penetrate the tent so it still helps to break them open and expose the larvae. Ground beetles and predatory wasps eat tent caterpillars, as do various birds, most notably Northern orioles. But your best strategy is to squash egg cases, tents, cocoons, and any caterpillars you see strolling around your yard. Wear an old shoe.


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