Skip to main content

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

  • Author:
  • Updated:

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


After long wait, storms eventually cancel Duran Duran concert

The newly inaugurated Rock 'N Roll Hall of Famers were kicking off their North America tour in Minnesota.

ITT Tech

Student loans cancelled for 1,380 Minnesota ITT Tech students

President Joe Biden moved to cancel the federal debt this week.

Screen Shot 2022-08-19 at 2.17.19 PM

Twine kills 2 young ospreys in Long Lake, Minnesota

One bird was found hanging by its leg from the nest.

Mindy Kiepe

5 Great Danes kill owner on northwest Iowa farm

The dogs were euthanized after the incident.

Becker Public Schools

School district sued by teachers' union over staff 'gag order'

The district has faced heightened scrutiny for months now.

Andrew Luger, former U.S. Attorney of Minnesota

After dozens of arrests, concern over rising 'militaristic' weapons on MN streets

The U.S. Attorney provided an update on the violent crime strategy in collaboration with federal and local law enforcement agencies.

Screen Shot 2022-08-19 at 1.31.41 PM

Outrage after ‘vote with bullets’ remarks from GOP Senate candidate

The candidate's comments were recently brought to light in a video recording.

State Patrol

2 killed after driver crosses center line near Silver Lake

A toddler in the vehicle survived the crash.

Screen Shot 2022-08-10 at 4.12.14 PM

The answer to winter woes: St. Paul's upcoming Palm Springs-style supper club

Take a first look at inside the menu at The Apostle Supper Club.