Forest Tent Caterpillars

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Last spring/summer, many residents may have noticed an upsurge in large silky caterpillar nests adorning their trees. These nests are home to the popular forest tent caterpillar, an overpopulated species notorious for overconsuming the foliage of trees, and they are expected to make another return this spring.

The City’s Forestry department has provided the following information this year to help residents better understand the insect:

What are they?

Currently, populations of forest tent caterpillar are found to be increasing in many parts of the City of Ottawa. Forest tent caterpillars are native insects that can periodically reach high population levels and feed on the leaves of several tree species. As a caterpillar, this insect will feed on leaves of tree species such as poplar, birch, maple, and oak. Caterpillar feeding occurs during the months of May and June. In July, the insect will become a moth and lay eggs which overwinter for the following season.

 

Forest tent caterpillars have a similar life cycle to other tent caterpillars, with one distinct difference: instead of building tent-like webs, they make a type of silken mat on the trunk or branches where they collect to rest, leaving only to feed on the leaves. These caterpillars are black, and have a series of white spots on their back. The adult moth is a yellow-brown colour.

 

What is the City doing about it?

The City has communicated with the Ontario Ministry of Natural Resources and Forestry, and they report to be monitoring the issue with increased populations of this insect in other areas of the province, including around Kemptville. City staff continue to monitor this issue.

What might residents notice?
Residents may see large groups of caterpillars on tree trunks and branches and some loss of leaves (defoliation) on trees this spring as a result of this insect. Healthy trees are able to sustain loss of leaves and some trees will produce a second flush of leaves in the same season following leaf loss. It is only repeated years of caterpillar feeding that cause concern with tree health.
Should residents be concerned?

On their properties, residents can consider the following to reduce damage to trees and reduce caterpillar numbers:

  • Caterpillars can be physically removed with a broom or knocked down with a stream of water from a garden hose.
  • Burlap can be attached to the trunk of trees just below the lowest branches. The burlap can be attached with a string in a band around the trunk and folded in half. Often caterpillars will congregate in the burlap and this can be disposed of daily in compost etc.

 

For more details about this insect, please visit https://www.ontario.ca/page/forest-tent-caterpillar