The wave of forest tent caterpillars arrived sooner than expected this year. But the good news for those who have been spraying down their walls and wrapping tin foil around their trees is that they’ll be leaving sooner than expected, too.
“We expected them to cocoon in the last week of June but it looks to be in about a week-and-a-half they’ll be entering the pupal stage,” said Mark Breon, a forest health technician with the Ministry of Natural Resources in Fort Frances.
The caterpillars then will transform into moths, which will be light brown or beige in colour, and hatch three weeks later (early July).
“Then they’ll stick around for between one and two weeks, lay their eggs, and die out,” noted Breon, adding the moths lay their eggs around the twigs of trees.
Meanwhile, Breon also said the army worms haven’t been as ravenous as some feared.
“Right now, they’re sticking to their preferred host trees, like trembling aspen,” he noted. “Like right now, on Highway #71 between Emo and Kenora, almost every trembling aspen has suffered severe to moderate damage.
“But they haven’t really hit their non-preferred host trees so as far as that goes, our forecast seems to be pretty accurate,” he added.
As they mature, the caterpillars may become hungry enough to move beyond their preferred host trees–such as aspen, oak, apple, birch, and all maple except red–to almost any species, including conifers.
And as people search for the “perfect” way to keep the pests at bay, Breon noted there’s no easy solutions.
“Everyone has their own remedy, whether it’s soap and water, or using a registered pesticide,” he said. “I’ve seen a few people using tin foil around trees, which is their own choice.
“But they should be sure to put it high in the tree, into the shade, so the sun doesn’t beat down and cook the bark,” he warned.
In related news, Breon noted rumours the MNR is importing a “friendly fly,” which resembles a large black fly, to combat the caterpillars just aren’t true.
“There is a species of insect, which is a natural parasite and an enemy of the forest tent caterpillar, which people call the ‘friendly fly,’” he explained.
“The flies lay an egg on the caterpillar’s cocoon and this egg turns into a maggot, which kills the caterpillar while it’s pupating. But it was not brought in by the MNR to fight forest tent caterpillars,” Breon stressed.
Forest tent caterpillars–which are distinguishable by their silky hair, blue stripe down their side, and white keyhole markings on their backs–have had outbreaks in Ontario every 10-12 years since the first recorded account in 1834.
At the peak of the last outbreak in 1991 in Ontario, the army worms covered more than 18.8 million hectares.
Next summer will mark the third–and peak–year in the forest tent caterpillar’s four-year cycle.