Forest tent caterpillar invasion looms in northwestern Ont.

The Ministry of Natural Resources expects an outbreak of forest tent caterpillars to expand in northwestern Ontario this year.

Insect expert Taylor Scarr said the caterpillars will eat most of the leaves from trees in an area spanning more than a million hectares — and the cold winter won't stop the infestation.

"This insect, forest tent caterpillar, is adapted to our cold weather ... it's sitting there inside the eggs on the branches,” he said.

“It's actually sitting there as a tiny caterpillar inside the egg, but it is relatively cold-tolerant at this time of year.”

Scarr said cold weather could kill forest tent caterpillars if it happens for several days in the spring, after the insects have emerged from their eggs. 

The infestation is expected to include areas in Kenora, Dryden, Sioux Lookout and Fort Frances, and it could also reach Thunder Bay.

Scarr said the caterpillars affect more than trees. 

"They'll start to look for a place to pupate ... to spin their cocoons ... then they're crawling up on people's houses and buildings ... on top of decks... they can become quite a nuisance."

Scarr said people need to be patient, as the outbreak will last a couple of years. Most trees — despite being defoliated by the insects — will survive, and then the caterpillars will be gone. Outbreaks of forest tent caterpillar infestations happen about once every 10 years, he added.   

Scarr said people should not cut down their trees when they see forest tent caterpillars in them. Alternatively, homeowner can use an insecticidal spray that's safe for organic use, or put sticky bands on the bottom of trees to stop caterpillars from climbing up the trunks.