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This Caterpillar Infestation in Saskatchewan Is the Stuff of Nightmares

They’re wiggling, hairy, and stripey blue.

by Emily Senger
Jun 10 2016, 12:00pm

Forest tent caterpillars outside the washroom in Moose Mountain Provincial Park. Image: Melissa Lebersback

Millions of wriggling, hairy, blue-striped caterpillars are eating and pooping their way through the Canadian prairie province of Saskatchewan, in the worst forest tent caterpillar infestation the area has seen in well over a decade.

Melissa Lebersback, a resident of Weyburn, Sask., went camping at her usual spot in Moose Mountain Provincial Park, near the Manitoba border, on the weekend of June 4 and 5 and found the women's washroom unusable due to a giant mass of caterpillars blocking the front door.

"They were two-to-three inches thick on the ground in front of the door," she told me. She posted a photo of the caterpillar pile on Facebook, which has since been shared more than 6,000 times.

Forest tent caterpillars in Echo Valley Provincial Park, Saskatchewan. Image: Ministry of Parks, Culture and Sport, Government of Saskatchewan

Forest tent caterpillars have been an issue in parts of Saskatchewan for the past three years. But this year is the worst, with much of the southern and central part of the province blanketed by the little wigglers. In a phone call from his office in Regina, Glen Longpre, the manager of landscape protection for Saskatchewan Parks, explained that the caterpillars are native to the Prairies and pose no real danger. (They've been seen in other provinces, too, but apparently not in numbers that would rival the situation in Saskatchewan right now.)

The current infestation is part of a natural cycle, which repeats itself about every 10-to-15 years. The last big caterpillar infestation in Saskatchewan was around 2003-04, he said. But even if the caterpillars are natural, they're still a nuisance.

"I was out there last weekend in Echo Valley Park [just north of Regina] and they're crawling all over you," said Longpre. "Of course they're defecating material all over everywhere."

That's right. Caterpillar poop. All over everything.

Falling caterpillar poop "almost sounds like rain on the camper roof"

"Oh yeah," said Longpre. "It's like big black pepper flakes. When you're sitting there, when it's quiet, you can hear it raining down. It's not pleasant." (At this comment, Karen Webb, the SaskParks spokesperson who was also on the call, burst into laughter.)

Lebersback confirmed the caterpillar poop phenomena.

"It's like a little hard black pellet. When you're sitting, it falls all over you," she said. "It almost sounds like rain on the camper roof."

The ick-factor gets worse. Though birds don't eat the forest tent caterpillars, the Sarcophaga aldrichi population, commonly known as the friendly fly, often swells along with a caterpillar infestation. The flies deposit their larvae directly into the caterpillar cocoon. The larvae then feast on the caterpillar pupae, killing the growing moth inside. Good, right? Yes, until fly maggots drop out of the tree and onto your head.

Oh, and the flies also regurgitate. Yep, puking flies.

The current forest tent caterpillar infestation started back in the summer of 2015, when the female moths laid their eggs on tree branches, hundreds of them in a single egg band, said Lonpre. The eggs then over-wintered on the branches. The past winter was mild in Saskatchewan, meaning millions of the eggs survived and hatched in the spring.

A photo from the government survey of caterpillar egg masses in Great Blue Heron Provincial Park in March 2016. Image: Ministry of Parks, Culture and Sport, Government of Saskatchewan

The forest tent caterpillar pupae are very hungry when they emerge after a winter of cocooning. Their favourite thing to chow down on is the trembling aspen, a tree in great supply on the prairies, but other trees and shrubs will also do.

During its most frenzied period of eating, a single caterpillar can consume up to seven leaves. Multiply that by millions of caterpillars and they can do some serious damage.

"Basically, it looks like fall here now," said Longpre.

However, the caterpillar-caused defoliation doesn't usually kill the trees. The entire caterpillar life cycle is only six weeks, so the leaves regrow later in the summer.

Saskatchewan Parks does monitor the caterpillar population by counting egg masses on frozen branches in the winter months and then doing some limited aerial spraying in parks and other high-use areas, such as campgrounds, based on what they find. The pesticide used, Bacillus thuringiensis kurstaki, is actually a bacteria that is toxic to caterpillars, but not to other species. The downside: it takes six weeks to make and has a short shelf life. "You can't store the product. It goes inert," said Longpre. So, unfortunately, the application now is over for this year and the current caterpillars are here to stay until the end of their lifecycle.

Forest tent caterpillars in Echo Valley Provincial Park, Saskatchewan. Image: Ministry of Parks, Culture and Sport, Government of Saskatchewan

There is some good news. The hungry caterpillars will disappear soon, forming cocoons, where they will live for five-to-10 days before emerging as beautiful… well… just as furry orangish-brown moths. The nocturnal moths lay their eggs and then die, surviving only 5 or 6 days in total.

So, somewhere near the end of July, residents of Saskatchewan can look forward to the caterpillars dying off and a week-long plague of moths descending upon them.

Saskatchewan residents should also hope for a cold snap in January. "If you do get some hard, cold weather, it's a good sign for helping to control the hatch for next year," said Longpre.