People in some parts of central and northern Minnesota have been finding themselves inundated by forest tent caterpillar, also called armyworms. The caterpillars feed during May on a wide variety of trees and shrubs, especially aspen, birch, linden, and oak. As they become fully grown, they move down the trees and start crawling on the ground to do some last minute feeding and looking for places to pupate.
|Forest tent caterpillars crawling up a house; unfortunately,|
there are few good options when these insects are numerous.
Photo: Jeff Hahn, UMN Extension
This brings them onto lawns, gardens, homes and other building, and essential any object they encounter. Interestingly while people generally did not notice forest tent caterpillars feeding in trees this year, it is hard to miss large numbers moving across a property. Unfortunately, a resident’s options are limited. For those found in lawns, they are not injuring the grass and treatment is not necessary.
However, when they get on buildings, people can try physical removal, e.g. taking a broom and sweeping them off and/or spray the exterior with an insecticide treatment, such as permethrin. Be sure that the product is labeled for use around the outside of buildings. Be extremely careful when making an application near water so pesticide does not move into surface water.
However, if there are a lot of caterpillars, neither of these methods will completely control them. People will ultimately have to patient until they eventually go away on their own.