There are caterpillars and tent-like structures in the crotches of my crabapple tree. How do I get rid of them?
The caterpillars are likely eastern tent caterpillars. Eastern tent caterpillars emerge in late April and early May from eggs that were laid on small twigs last summer by female moths. The caterpillars feed on the buds and foliage of apple, crabapple, wild plum, cherry, and similar trees. On cloudy rainy days and at night, the caterpillars remain in the protective confines of their tent. On warm sunny days, they go out and feed on the tree's buds and foliage. Tents are initially small, but are gradually enlarged as the caterpillars feed and grow in size. The caterpillars are full grown about 6 weeks after hatching.
While eastern tent caterpillars may defoliate branches or portions of a tree, they do not seriously harm most healthy, well-established trees. The defoliated branches will leaf out again in a few weeks. Trees may be seriously weakened if heavily defoliated in several consecutive years.
Damage to trees can be minimized by removing and destroying the tents and caterpillars as soon as they are noticed. Tent removal should be done in early morning, late evening, or on cool rainy days when the caterpillars are gathered in their tents. The tents and caterpillars can be removed with a broomstick, forked branch, or by hand.
Do not attempt to burn the tents and caterpillars. This is a dangerous procedure that may injure the tree.
It is seldom necessary to control eastern tent caterpillars with insecticides. If insecticides are used, they should be applied when the caterpillars are small. Insecticides are less effective on mature caterpillars. Spray the tree's foliage within 2 feet of the tents. (Tents are water repellent so spraying them with water based insecticides are not very effective.) Effective insecticides include Bacillus thuringiensis (Dipel, Thuricide, etc.) and carbaryl (Sevin).