REGIONAL— With a week or so to go before tent caterpillars complete their leaf-munching stage, it now appears that the worms will leave only spotty defoliation in their wake this year.

“There’s a little less defoliation than I expected,” said Mike Albers, forest pest specialist for the Department of Natural Resources in Grand Rapids. The rainy, cool weather in June likely slowed the development of the caterpillars this spring, according to Albers, and that reduced the amount of defoliation, at least so far. But Albers notes that the caterpillars eat most voraciously when they reach their full size, and that most of the worms are just starting to reach that point— so more defoliation is still possible.

Forest tent caterpillar populations have been slowly building for the past couple years, and DNR officials had predicted last year that 2014 could see significant defoliation.

The most significant defoliation so far in northern St. Louis County appears to be in a swath running from central Vermilion Lake Township into portions of the Britt area. Patches of young aspen along Hwy. 169, between the Y Store and the Black Bear Café, have seen significant to almost total defoliation as a result of the worms.

In most other places, Albers said the damage is mostly limited to single trees or small groups of trees.

“But we do have a lot of “friendly flies” in some places,” noted Albers, referring to the parasitic flies that lay their eggs in tent caterpillar pupae. The flies don’t bite people, but their tendency to cling persistently to any object, including humans, is responsible for their common name. Contrary to rumor and legend, the DNR did not introduce friendly flies, which are native flies that have parasitized tent caterpillars for many years. While the friendly flies are a nuisance, they are largely responsible for helping to stem outbreaks of tent caterpillars, which can cause large areas of defoliation and nuisance problems of their own.

DNR officials will have a better idea of the extent of defoliation in a couple weeks, when they complete an aerial survey of northeastern Minnesota forests.