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Caterpillars are infesting Canadians’ yards, but researchers say not to be alarmed

Forest tent caterpillars are pictured on Manitoulin Island, Ont., on June 6, 2018.

John Savage

John Savage has spent several afternoons in the past week vacuuming caterpillars off his property on Manitoulin Island in Ontario’s Lake Huron. He admits it has been “a totally futile operation.”

“There are billions of them,” Mr. Savage said. “They are on the trees, they are on the roads, they are on your deck, they are in your driveway ... they climb the houses, you name it.”

Mr. Savage’s yard isn’t the only place in Canada these caterpillars have infested. The fuzzy, slow-moving creatures have crawled their way right across the country, from Nova Scotia, to Alberta, to pockets of British Columbia. The caterpillars are appearing in huge numbers this season, particularly in Northern Ontario and around Ottawa, but scientists say it is not a cause for alarm.

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“They’re always in the forest,” said Amanda Roe, a researcher with Canadian Forest Service. “It’s just whether there are enough of them there that people really start to notice.”

According to Dr. Roe, the caterpillars currently seen coast to coast are forest tent caterpillars, whose population hits a peak every 10 to 12 years. While the numbers vary per region, researchers say Canadians are now in the midst of a caterpillar outbreak.

Forest tent caterpillars feed on Trembling Aspen and other deciduous trees, which are commonly found in Canada’s boreal forest, according to Dr. Jens Roland, a retired professor with the University of Alberta’s department of Biological Sciences. As they chew their way through the forest’s canopy, they eventually begin crawling towards homes and yards looking for more food.

“They move out of the trees, and that’s when they start moving onto your house,” Dr. Roland said.

“Most people have a childhood memory of when the caterpillars were bad,” Dr. Roe said. Some regions tend to be worse than others, she added.

Mr. Savage said he remembers seeing a caterpillar infestation as a child growing up in Kirkland Lake, Ont. But he maintains this year is one of the worst he has ever seen, particularly on Manitoulin Island, his home for the last 20 years.

Forest tent caterpillars can be a nuisance to both homeowners and entire municipalities as well. Luc Adam, a spokesperson for Quebec’s Ministry of Transportation, recalled an instance in the early 2000s when warning signs were put up to caution drivers of caterpillars crossing a highway between Beaudrie and Rouyn-Noranda.

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“They cross the road at the same place ... and they get crushed,” Mr. Adam said, comparing the potential safety hazard to an oil spill or an icy patch on the road. The caterpillar population has hit a peak in the region during the last few years, he said, but nothing quite like the previous highway scare.

Dr. Roe said there are no exact numbers yet on the scale of the caterpillar infestation this year, as the Ontario Ministry of Natural Resources has yet to conduct aerial surveys of the province’s disappearing forest canopy, but she says 2017 was a peak year across the region.

Caterpillar-related nuisances are not only exclusive to forest tent caterpillars. Eastern tent caterpillars, their cousin species, are also known to be a springtime problem for regions in Eastern Canada. They are responsible for webs resembling cotton candy that can be found engulfing tree branches.

The two species are often confused with another, Dr. Roe said, as many believe the eastern tent caterpillars are responsible for the webs, when in fact they are not. One simple way to tell them apart is to look at the markings on their back, Dr. Roe said. Forest tent caterpillars have white markings on their back and blue stripes on the side, while eastern tent caterpillars have one, single straight line down the back.

Residents in affected regions say they have tried multiple methods to rid themselves of the caterpillar infestation. Sherry Hunt, who lives in Espanola, Ont. roughly 100 kilometres northeast of Manitoulin Island, said she has resorted to parking behind her home to avoid the caterpillars in her driveway.

“Just trying to get to your vehicle was a bit of a sport,” Ms. Hunt said. She attempted to use a mixture of water, soap, vinegar and detergent to ward off the caterpillars. While it proved to be effective, she said the cleanup can get quite messy.

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Dr. Roland said pesticides can be helpful as well, but the sheer volume of caterpillars makes controlling the population “impossible.” For Mr. Savage, the preferred method is a vacuum.

Dr. Roe said worried residents can spray the caterpillars away with a water hose, but they should not be worried for much longer, since the caterpillars will pupate in a few weeks and begin the transition to their next life cycle – becoming a moth that will lay eggs that will hatch next spring. These moths only live for a day or two, Dr. Roe said.

“Two weeks from now, people won’t see them at all,” Dr. Roland said, and they become “out of sight, out of mind.”


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