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'Army worm' sightings in Thunder Bay don't mean a new invasion is imminent (3 Photos)

An MNRF expert says the next big infestation is likely years away.

THUNDER BAY — An expert with the Ministry of Natural Resources and Forestry says sightings of "army worms" in the Thunder Bay area don't necessarily point to an imminent invasion.

Recently, some local residents have posted photos of forest tent caterpillars.

In years when there are heavy infestations, outbreaks in Northern Ontario can cover millions of hectares and lead to extensive defoliation of hardwood trees such as poplar and white birch.

Some trees may die, but most will rebound and produce new leaves.

However Dan Rowlinson, provincial lead for the Ministry of Natural Resources and Forestry's forest health monitoring program, says the last significant infestation in Northwestern Ontario collapsed in 2017.

Outbreaks may last three to five years before going dormant for a decade.

"It's actually something you can set your clock by. About every 10 years, you'll see an outbreak flare up. So we're still in the green in the northwest part of the province," Rowlinson told TBNewswatch.

Thunder Bay entomologist Ken Deacon said the caterpillars can still persist as small, local populations between outbreaks.

During outbreaks, Deacon said, "They're usually pretty abundant by now. I remember back in the 80s, it looked like autumn at the end of June. The poplar and the birch get really hammered."

The forest tent caterpillar gets its name from the silk mats in which it rests in foliage.

Rowlinson noted that people sometimes confuse it with a different insect, the eastern tent caterpillar, which forms a communal tent in the crotches of tree branches.

"When you're seeing those tents along the roadside, in shrubs and so on, that's not the forest tent caterpillar. I was working in the Northwest the last few weeks and I noticed they are quite visible along the roadways," he said.


Gary Rinne

About the Author: Gary Rinne

Born and raised in Thunder Bay, Gary started part-time at Tbnewswatch in 2016 after retiring from the CBC
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