They're about to attack, but don't call them "Army" worms

Publish date:

The Duluth News Tribune reports summer 2014 is likely to bring a massive infestation of forest tent caterpillars. Those planning weddings or camping trips should know what they may be in for.

The last major outbreak, in 2001, defoliated 8 million acres of forest. Those too young to remember it would do well to take heed.

The insects hatch in May, emerging as small caterpillars to munch on new leaves. They eat and eat, then spin cocoons, or tents, where they change into small brown moths.

They have various obnoxious ways to make their presence known, from plopping onto picnic tables to raining down greenish-black excrement from trees above.

Eventually they run out of food and starve to death before they can mature. Flies love to feed on them, so fly numbers multiply after the caterpillars emerge. They're called friendly flies because they don't bite people, but they are large and buzzy and land on people even though they don't bite.

The news is based on aerial surveys released in a report this week. It called 2013 "a building year" that usually precedes an outbreak.

The 2013 DNR update includes a graph showing big peaks occurring approximately every 12 years, and lasting for 2 to 3 years. You can see last summer's rapid expansion.

Bug experts have learned to predict outbreaks based on population spikes rather than passage of time. They don't know whether the peak will come in summer 2014 or summer 2015.

Experts will know more after counting egg masses on trees later this winter. Because they are natives, they are well-adapted to cold temperatures and won't have any trouble staying snug in their tree branches.

Most healthy trees can bounce back from defoliation. But if they are stressed from drought or other pests at key times during the summer, they can die. With each major outbreak, about 10 percent of defoliated aspen trees die.

Of course, because it's nature, there is a silver lining. Weeks of defoliation can help species on the forest floor get enough sunlight to grow. Caterpillar poop helps fertilize the soil. Finally, the caterpillars give Minnesotans something to complain about during summer.

Next Up