Once again, the eastern tent caterpillars (Malacosoma americanum) have become apparent in Iowa landscapes and along the highways. The caterpillars can go largely unnoticed; it’s the unsightly, silken ‘tents’ in the crooks of branches of the tree or shrub that are obvious. Tents start out very small but enlarge as the caterpillars feed and grow and add to the tents, making them more obvious in the landscape as the weeks go by.
Eastern tent caterpillar populations vary greatly from year to year and place to place. When they do appear, the caterpillars feed on buds and foliage a variety of trees and shrubs but prefer apple, crabapple, wild plum, cherry and similar trees.
An earlier newsletter article that includes a video about eastern tent caterpillars: https://hortnews.extension.iastate.edu/2015/05-08/tentcaterpillar.htm
ISU Horticulture & Home Pest News Encyclopedia article: https://hortnews.extension.iastate.edu/eastern-tent-caterpillar
Tents that are not discovered until late May can be ignored as the caterpillars have nearly finished feeding and are at their maximum size of 2 to 2.5 inches long. Spraying the foliage in an attempt to kill caterpillars as they feed is no longer warranted as insecticides are generally ineffective against grown caterpillars. Where it can be safely done, remove and discard the tent and remaining caterpillars as in early morning or late evening or on cool rainy days when the caterpillars are inside the tents.
There is only one generation of eastern tent caterpillars each year. As we used to say back in the day, “What you see is what you get.”
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 22, 2020. The information contained within may not be the most current and accurate depending on when it is accessed.