Question
My crabapple tree has an infestation of small (1'2 to 1 " long) black worms that appear to be living in funnel shaped spider web like nests.  What do I do?

Answer
This is Eastern tent caterpillar.
The eastern tent caterpillar overwinters as an egg, within an egg mass of 150 to 400 eggs. These masses  are covered with a shiny, black varnish-like material and encircle branches that are about pencil-size or smaller in diameter.

 

The caterpillars hatch about the time the buds begin to open, usually in early March. These insects are social; caterpillars from one egg mass stay together and spin a silken tent in a crotch of a tree. Caterpillars from two or more egg masses may unite to form one large colony. During the heat of the day or rainy weather, the caterpillars remain within the tent. They emerge to feed on leaves in the early morning, evening, or at night when it is not too cold.



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. As the larvae feed on the foliage, they increase the size of the web until it is a foot or more in length. In 4 to 6 weeks the caterpillars are full grown and 2 to 2-1/2 inches long. At this time, they begin to wander away individually from the nest in search of protected areas to spin a cocoon. The cocoon is about 1 inch long and made of closely woven white or yellowish silk and is attached to other objects by a few coarser threads.



The adult moth  emerges from the cocoon about 3 weeks later. The moth is reddish-brown with two pale stripes running diagonally across each forewing. Moths mate and females begin to lay eggs on small branches. The eggs will hatch next spring. There is just one generation per year.

Natural enemies play an important role in reducing eastern tent caterpillar numbers in most years. Caterpillars are frequently parasitized by various tiny braconid, ichneumonid, and chalcid wasps. Several predators and a few diseases also help to regulate their populations. This, in part, accounts for the fluctuating population levels from year to year.
Prevention and early control is important. Removal and destruction of the egg masses from ornamentals and fruit trees during winter greatly reduces the problem next spring. In the early spring, small tents can be removed and destroyed by hand. Larger tents may be pruned out and destroyed or removed by winding the nest upon the end of a stick. Burning the tents out with a torch is not recommended since this can easily damage the tree.
Young caterpillars can be killed by applying an insecticide containing Bacillus thuringiensis var kurstaki. Other insecticides include carbaryl, methoxychlor, and malathion. Larvae within the tents are protected beneath the webbing and are more difficult to kill with an insecticide.

While the Eastern tent caterpillar does eat the early leaves of trees and shrubs, the defoliation usually does little damage to trees, and rarely do trees die from an infestation.  The lack of damage is due to the timing not the severity of the defoliation. Because the caterpillars hatch as soon as the young leaves unfurl in the spring, the tree has put little energy into the leaves and typically re-foliate in June, seemingly no worse for wear. The young caterpillars venture out to feed on leaves during the night and return to the tents for protection during the day. They will feed on most kinds of fruit trees, many hardwood trees such as ash, maple and oak, and other plants in the rose family, like ornamental crabapples and plums, and even pyracantha.

Here is a web link to pictures and more information .
http://www.umassgreeninfo.org/fact_sheets/defoliators/eastern_tent_catepillar.ht...