Montrealers 'don't need to fear' tent caterpillar invasion

The swarms of caterpillars popping up around Montreal are, for the most part, harmless but should be treated with caution, a l'Université de Montréal entomologist says.

Forest tent caterpillars are mostly harmless but should be handled with care, entomologist says

In some cases, tent caterpillars can cause itchiness and rashes. The culprit? Those long, golden hairs. (Pascal Guay)

Swarms of forest tent caterpillars have been popping up around leafy areas of Montreal, alarming some people who have heard that the species is dangerous.

However, Étienne Normandin, an entomologist and collection manager at l'Université de Montréal, says Montrealers "do not need to fear" the tent caterpillar.

Forest tent caterpillars can be identified by the two bright blue lines that run along the top of their bodies and their long, golden hairs.

While these hairs can sometimes cause itchiness and rashes, they don't present a serious danger to humans or pets, Normandin says.

Confusion between species causes alarm

Some news sources have reported the caterpillars could cause severe allergic reactions, prompting at least one Montreal school to issue a warning to parents and students.

However, Concordia University biology professor Emma Despland said that harmless tent caterpillars are not to be confused with the pine processionary caterpillar, which can be dangerous.

These critters, which can be deadly if consumed by pets, are confined to Europe, Despland said.

While tent caterpillars are for the most part harmless, they should only be picked up with gloves to avoid the risk of any reaction, said Normandin.

"If you do touch them, you need to wash your hands with a really good soap," he said.

Normandin said it's normal for people to overreact when insects pop up unexpectedly, especially when they appear in large swarms, which can be alarming.

"When insects are involved, a lot of people overreact. It's a normal reaction."

The caterpillars live in large swarms as a defensive tactic against predators. 

Caterpillars can damage trees

Normandin said by July, the caterpillars will have metamorphosed into brown moths.

Until then, they will be ferociously gobbling up leaves to store up energy for their transformation. However, gardeners with low-growing plants or vegetable gardens don't need to be concerned, he said.

"[They're] not going eat your cabbage or your tomatoes, but they will eat the cherry trees, the ash trees and the apple trees," said Normandin.

Tent caterpillars can be dealt with using pesticides or, if the swarm is small, by simply picking them off the branches.

Tent caterpillars have also appeared in large numbers in other parts of Canada, including Regina, Winnipeg, Toronto, and parts of northwestern Ont.

Population outbreaks are cyclical, which means Montrealers can expect to see them each spring for the next two to three years.