Tent caterpillars are called such because they can be found in the crotches of trees in large groups (upwards of 300) surrounded in a web-like substance that resembles a tent. These tents appear in trees in spring and midsummer.
There are two types, Eastern tent caterpillar and Forest tent caterpillar. They’re both hairy and form “tents”, webs to live in.
Forest tent caterpillars are the more destructive of the two:
In Minnesota they attack a number of broadleaf trees and plants like quaking aspens, balsam poplar, basswood, oaks, ashes, birches, alder and fruit trees.
- Feeding damage by these caterpillars slows down the growth rate of deciduous trees.
- When target trees are defoliated, forest tent caterpillars may also damage other nearby plants.
- Damage can be seen on vegetables, fruit trees and other small fruits, and nursery crops.
- They are a nuisance when they are found around buildings or on roads.
Forest tent caterpillar are very hairy. They are also heavy feeders. They can devour surrounding foliage and many strip whole trees.
Forest tent caterpillars photo from Duluth News Tribune
Easter tent caterpillars:
- Eastern tent caterpillars are found on fruit trees like apple, chokecherry, crabapple, plum and cherry in May and June.
- The larvae feed on leaves, sometimes defoliating trees.
- Larvae make a noticeable web or ‘tent’ in the fork of the branches.
- The tree is covered in webbing and is defoliated when the caterpillar population is high.
- These caterpillars generally do not affect tree health.
- Young trees, as well as unhealthy, stressed trees, suffer more damage and are more susceptible to feeding damage and may need to be protected.
Eastern tent caterpillar photo by University of Kentucky
Eastern tent caterpillar nest photo by University of Kentucky
How to Control the Tent Caterpillar:
- Remove and destroy egg masses from branches of small trees before eggs hatch in the spring.
- Pull the webbing down when the caterpillars are inside at the end of the day or when it rains.
- Use a spray of water to knock caterpillars off if they’re on your buildings.
- Be careful not to crush too many caterpillars as they can smear and leave marks on some paints.
- If you plan to use pesticides, do so when the caterpillars are less than one inch or less. As they get to their full-grown size (two inches), the pesticides might no longer be effective. Bonide Eight is recommended, please read and follow directions on the label.
- Bacillus thuringiensis is a good option if the tree is flowering as it will not harm visiting honey bees and other pollinators.
Note: Sprays can be ineffective as the “tent” can keep spray from penetrating and getting to the caterpillars.
The experts at Gertens are always available to answer your questions!