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Forest Tent Caterpillars

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Forest Tent Caterpillars are fuzzy, blue-green, and will grow to about five centimetres long. Their eggs hatch early in the spring when the leaves begin to open. They build cocoons in June and emerge as moths in late July. While 2017 does not appear to be a mass infestation year in Fort McMurray, you may still see some and can take steps to eliminate the caterpillars in your yard.

The Problem With Forest Tent Caterpillars

Tree species affected by the caterpillar are aspen, poplar, ash, oak, maple, cherry and mayday. You may see caterpillars on the trunk, branches or among the leaves. The caterpillar will eat the green foliage and damage it, causing stress for the tree, weakening it and making it more susceptible to other types of stress. Trees usually re-leaf by July; however, this problem can be reduced by controlling the caterpillars.

How To Eliminate Forest Tent Caterpillars

Use a spray such as BTK insecticide (Bacillus thuringiensis var. kurstaki), which is available at most home and garden stores. You can also try mixing insecticidal soap with water and spray the caterpillars. You can get rid of the cocoons and egg cases by carefully removing them from the tree to avoid damaging the bark, and disposing of them in a sealed bag. Squishing the caterpillars, cocoons or adult moths is also effective.

Prevention Techniques

Cocoons are yellow to white and egg masses are shiny, dark brown or gray, and will straddle or wrap around tree branches.

One of the best methods of long-term control is to inspect your trees for egg masses in the fall, winter and early spring. Remove the mass by cutting off the affected branch and disposing of it in the trash.

Putting tin foil, grease or lard on the tree base is not advised as it can damage the bark.

More Information

For more information on Forest Tent Caterpillars, visit the Government of Canada’s website.


Contact us for more information on Forest Tent Caterpillars or to schedule an appointment with a Tree Doctor.

Parks Services: 780-799-5832
After hours: Pulse Call Line: 780-743-7000 (evenings, weekends and holidays)

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