Eastern tent caterpillars have been common in many areas of Minnesota this spring. This insect is easy to identify because it constructs a silken web in the fork of branches. They attack a variety of hardwood trees, especially fruit trees, including apple, crab apple, chokecherry, cherry. These caterpillars are bluish black with yellow and a white stripe running the length of the top of its body. They are also mostly smooth except for a series of hairs sticking out along the side of their bodies. They are two inches when fully grown.
Eastern tent caterpillars normally emerge late April to early May. This year they emerged several weeks early because of the unseasonably warm weather we experienced in March and April. As a result, most, if not all of the caterpillars are fully grown and finished feeding.
The best time to treat eastern tent caterpillars is when they are half full grown length or less, i.e. no more than one inch long. An easy non-chemical method to manage eastern tent caterpillars is to wait until evening or rainy days when the caterpillars are in their webbing, then pull it out along with the caterpillars. Then destroy the insects by bagging, burning, or burying them. Insecticides are an option. Because fruit trees are typically flowering when eastern caterpillars are active, use a low impact insecticide, such as Bacillus thuringiensis, spinosad, or insecticidal soap. If caterpillars are fully grown, then just ignore them.