Tent caterpillar outbreak for the fourth year in a row in northern Ont.

They’re gross and squishy and seemingly everywhere at this time of year – and their time is running out.

A provincial expert says the tent caterpillar outbreaks we’ve seen in northern Ontario for the last four years are coming to a close this or maybe next year.

Dan Rowlinson, provincial lead of Ontario Forest Health Monitoring with the Ministry of Natural Resources and Forestry, said the caterpillar outbreak this year is most severe in the Timmins area, all the way east to the Quebec border.

While the length of the outbreaks varies from three to six years, he said new outbreaks happen like clockwork.

“You can almost set your calendar by every 10 years somewhere in the province is going to be an outbreak,” he said.

“We're entering into four years, which I'm hoping is going to be one of the final years.”

Rowlinson said the tent caterpillar is native to North America and the outbreaks begin and subside naturally. As the number of caterpillars increase, so, too, does the population predators attacking them.

“So as the diseases and parasites build up in the population, they start to eat themselves out of house and home,” he said.

And as the large caterpillar population is beset by disease and parasite, they weaken. And in their weakened state, a fly emerges that plants parasites in the caterpillar larvae.

“And it will cause that widespread mortality,” Rowlinson said.

So how do outbreaks begin? He said it’s the reverse process. As the caterpillar population shrinks, food for the parasites disappears, and eventually parasites die off from lack of food, allowing the cycle to begin again.

This year’s tent caterpillar outbreak is just about done. In mid-June, they enter cocoons to emerge later as tiny moths that will be attracted to the lights outside homes. (Lydia Chubak/CTV News)

The north isn’t the only spot to see outbreaks. In southern Ontario, he said tent caterpillars tent to feast on oak and sugar maple trees, rather than poplar.

“You can have active tent caterpillar populations basically from Kenora to Cornwall,” Rowlinson said.

“They're not selective to specific areas. Currently we're dealing with one right now in the Northeast region, as I mentioned, in the northern part of the region.”

While they devour leaves, Rowlinson said that doesn’t mean they cause widespread damage.

Defoiliated, not dead

“A defoliated tree is not necessarily a dead tree,” he said.

“If they're severely defoliated they can put out a second crop of leaves in the growing season. So once for his tent caterpillar completes its annual cycle in the in the coming weeks, those trees will be defoliated for a few weeks and then they'll start to put on a second crop of foliage.”

This process allows the tree to store their root starches, he said, enabling them to survive.

“So although it looks devastating on the landscape, it's not as detrimental to the whole species as something like a Spongy moth would be,” Rowlinson said.

While largely benign, he said the tent caterpillar is certainly not “a very good people bug.”

“They are a disgusting bug from a homeowner perspective,” Rowlinson said.

“I mean they crawl on your decks and they can stain your laundry when it's on the line ... June is a popular time for outdoor weddings and family reunions things like that, and it's just sort of loses some of the pizzazz when you're having insects crawling all over your buffet.”

While unpopular, Rowlinson said they are part of the amazing natural landscape in Ontario.

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“It is, in fact, a wonder of nature, so get out there and check it out (and) learn a little bit about the insects (and) understand how they coexist in our natural environment.”

This year’s outbreak is just about done, he added. In mid-June, they enter cocoons to emerge later as tiny moths that will be attracted to the lights outside homes.

The moths then mate and lay eggs for next year.