What is it?

Forest tent caterpillars (Malacosoma disstria) is a pest of broadleaved trees and shrubs. They can completely defoliate a tree and cause tree health decline.

Symptoms

• Mature larvae are 4.5-5.5 cm long. They are hairy, dark brown to black color, with a board blue band along each side.
• They cluster together on the trunk or branches when they are not feeding.
• Trees are defoliated by their feeding.

Damage

• Trees are defoliated by the feeding of forest tent caterpillars.
• Trees generally can recover after attack
• However, heavy defoliation can cause tree health decline and more susceptible to other pests and diseases.
• Crushed caterpillar leaves marks on items.

What to do?

• Introduce natural predators like birds, parasitic wasps can control certain amount of the population.
• Scrape off egg band between fall and spring from infested plants.
• Wash off the caterpillar by using strong jet of water.
• Water your tree but don’t fertilize after an attack. Lush growth from nitrogen combined with defoliation will further stress your tree.

Other resources:

https://tidcf.nrcan.gc.ca/en/insects/factsheet/9374

https://gardening.usask.ca/articles-and-lists/articles-insects/article-forest-tent-caterpillar.php