Eastern tent caterpillar
Eastern tent caterpillars, Malacosoma americanum, are active this year in southern Minnesota. They are native defoliators, occurring from the Rockies to the east coast. Further east they are much more common than in southern Minnesota. Their favorite hosts are wild cherry, apple, and crabapple, but they occasionally feed on other deciduous trees.
Tiny caterpillars hatch from eggs in the spring about the time wild cherry leaves begin to unfold. The young caterpillars quickly gather at a major branch fork and begin to build a web from which they go forth to feed on newly opened leaves. Larvae spin a fine strand of silk wherever they go. As the caterpillars grow, so does the size of their tent. When populations are large, whole trees become covered with webbing and all leaves are devoured. There have been times when entire country sides have been populated with their silken tents. It is their tents that distinguish it from its close relative, the forest tent caterpillar.
The fully grown caterpillars are generally black with a white stripe down the back and a series of bright blue spots between longitudinal yellow lines. When the larvae reach this stage, they leave the host tree and search for a place to spin white cocoons; on fences, tree trunks, or other natural or constructed objects. The adults emerge in late June or early July. One generation occurs each year. This defoliation generally does not hurt the trees. They will refoliate and should do just fine.