Residents in St. Lazare are back shovelling their steps, but it’s caterpillars, not snow, they’re clearing away in buckets.
Droves of forest tent caterpillars have moved through southern Manitoba and Saskatchewan this spring, stripping foliage off deciduous trees and shrubs and leaving behind masses of squashed larvae and fecal matter.
Both the Municipality of Ellice-Archie and Upper Assiniboine River Conservation District have identified St. Lazare as a hot spot for the caterpillar invasion this year. Trisha Huberdeau, chief administrative officer for the municipality, said caterpillars have moved through the Assiniboine River Valley and inundated the community of 260 people.
“They sort of move in a path, I would say, so if the path has gone across the highway, you’ll see the highway just basically covered black, kind of like an oil slick almost. And then, for houses, if your house is affected — your yard is affected — then your trees will be all covered and eventually all of the leaves disappear,” she said. “The worms crawl up on the front of the house and kind of crawl over the deck and crawl over the grass. As bad as it is in some areas, you’ll actually be shovelling them away. I have a co-worker who actually has to shovel it away from her house. In other areas, it’s not so bad. You’ll sometimes get a few of them sort of on the ground and on the deck and on your walls that you’ll have to sweep off.”
Efforts to deter the caterpillars have been largely unsuccessful, according to Huberdeau. Chemical sprays have been effective short term, but dead caterpillars are quickly replaced.
“There’s not a lot that you can do, honestly,” Huberdeau said.
Similar scenes have been reported in other areas of Western Canada. In Dundurn, Sask., south of Saskatoon, Tammi Hanowski made headlines after sharing video of her caterpillar-carpeted farm while residents near Windthorst, Sask., shared images of roads covered with caterpillars.
The larvae stripped a quarter of wildlife habitat near the area, resident Joe Widdup shared over social media.
The Municipality of Ellice-Archie is not concerned about dead trees at this time, Huberdeau said. Only select trees are attractive to the caterpillars and those that do lose foliage often recover.
Despite being stripped of leaves, Jordan Bannerman, entomology instructor with the University of Manitoba, said trees may begin to flush again within weeks.
“It takes quite a few years — consecutive years — of defoliation to kill most otherwise healthy deciduous trees, so although it looks quite terrible, there really isn’t a huge risk for individual trees to be killed by forest tent caterpillars, even if the defoliation is very high,” he said.
The Upper Assiniboine River Conservation District, which counts St. Lazare in its northern region, also said it is not concerned over tree loss.
Ryan Canart, district manager, said damage has been, “pretty sporadic, but at the same time, pretty aggressive.” Trees survived last year’s caterpillar swarm, which caused significant leaf loss in the St. Lazare area, he noted.
The pattern holds through the affected area, he said, with some bluffs more defoliated than others, depending on tree type.
“(The caterpillars are) kind of up that west side of the province right out at the Saskatchewan border up as far as St. Lazare, for sure, and then it kind of peters out to the north of that,” Canart said.
What goes up…
Manitoba is at the peak of its forest tent caterpillar boom-bust cycle, Bannerman said. Like most butterflies and moths, the notorious defoliator will peak for several years every 10 to 20 years in a region.
“In terms of Manitoba, what’s been going on is a number of years ago the populations first started really increasing sort of in the Interlake area, so a ways north of Winnipeg, and then it kind of progressively spread south and east such that last year and this year as well are pretty heavy years for Winnipeg and all of the surrounding area. Now, it’s actually spreading to the west,” he said, noting the species largely spreads through the adult moths, which emerge in early July.
This year is year two of peak tent caterpillar activity for parts of the province, including Winnipeg, and populations will likely decline in upcoming years, he added.
The species averages two to three years of high population before dropping down.
“It varies, but there are a number of natural controls that just cause the populations to crash, and that’s mainly viruses that are naturally in their populations and also parasites,” he said. “There are species of flies and wasps that kill the caterpillars and they really increase in numbers in an area where there’s an outbreak.”
This year’s problem is expected to drop off in the next weeks as larvae begin to pupate, he said.