'They're really harmless': Tent caterpillar population explodes in northeastern Ontario

Sudbury and many other parts of northeastern Ontario are at the centre of an outbreak of tent caterpillars, as the insects' population has exploded.

Chris McQuarrie, an entomologist at the Great Lakes Forestry Centre in Sault Ste. Marie, Ont., says the caterpillars, which eventually transform into tent moths, experience outbreaks every 10 years on average.

"Normally the insect gets controlled by diseases and predatory parasitic wasps and flies that eat the caterpillars," he said.

"And every once in a while, whatever these conditions are that limit them go away for a little bit and we get a big outbreak."

McQuarrie says researchers don't fully understand why some years those conditions don't keep the tent caterpillar population in check.

But the end result is that some trees in Sudbury, and other parts of northeastern Ontario, are covered with hordes of the insects and often stripped of their leaves.

Some species in the tent caterpillar family build tent-like structures with their silk, which is where they get their name.

The species most commonly found in northeastern Ontario doesn't build the silken tents, but are part of that caterpillar family nonetheless.

While a large group of caterpillars might appear distasteful to some, McQuarrie says they should not be a cause for concern.

"I remember years ago hearing about a school where they were kind of hanging around the doors and kind of grossing people out. They're really harmless," he said.

Birds are a top predator for the caterpillars, but they can also fall victim to parasitic flies that lay their eggs on them.

"Then the fly larvae eat those caterpillars," he said.