Northwest Minnesota dodges brunt of tent caterpillar infestation

Forest tent caterpillars have been making the news this spring as the creepy-crawly leaf munchers chew their way across parts of Minnesota, but the northwest part of the state appears to have escaped the worst of the outbreak.

For this year, at least.

"I think it's kind of a 'brace yourself' situation -- maybe," said Jana Albers, forest health specialist for the Department of Natural Resources in Grand Rapids, Minn. "There's not much going on right now that we know of (in the northwest). We did have significant acres in Mahnomen County and Beltrami County as far north as Red Lake."

Native to Minnesota and forested areas of North Dakota, tent caterpillars typically occur in 10- to 12-year cycles. They'll build up for two or three years, Albers said, a couple of peak years will follow, and "they basically eat themselves out of house and home."

The cycle then repeats itself. According to Albers, the next "Big One" appears to be two to three years off.

"We noticed some last year, and this year, quite a few more people are calling in," she said. The last tent caterpillar outbreaks in northwest Minnesota peaked in 2001.

Adam Munstenteiger, area forestry supervisor for the DNR in Warroad, Minn., said reports that far north have been spotty. Tent caterpillars also have been reported in parts of northeast North Dakota, according to the North Dakota State University Extension Service.

"We try and tell people, while they are a nuisance, they are for the most part a pretty benign force of nature," Munstenteiger said. "We'll get them bad for one year and things will taper off and we'll be good for a few more years."

Two populations

Albers said Minnesota has two populations of forest tent caterpillars. The northern Minnesota population occurs in cycles, she said, while caterpillars in the west-central part of the state are sporadic, but always present across a fairly broad area.

This year's outbreak appears to be worst in northeast Minnesota, but Albers said the DNR won't know the extent of the infestation until September, when it compiles results from an aerial survey set to begin next week.

The annual survey takes about 2½ months to complete, and covers 13 million acres.

The good news is that while the tent caterpillars cause widespread defoliation of trees such as aspen, basswood and oak, they rarely do permanent damage, Albers said. The caterpillars now giving people the creeps will crawl into cocoons in the next week or so, she said, and most trees should have leaves back by July 4.

Albers said she's getting about 20 calls a day, mostly of the "ick" variety, from homeowners and property owners wondering how they can keep the caterpillars out of the yard or off their patios. She said the DNR offers several tips for minimizing the impact on its website, but a bacterial control known as Btk -- short for Bacillus thuringiensis -- is recommended. Btk works well to control smaller caterpillars but has no effect on birds, humans, other animals and most other insects.

Pick your battles

In terms of bracing for the inevitable "Big One" that's coming in a year or two, Albers said all she can recommend is turning out porch lights and yard lights at night to attract fewer of the moths that will emerge later this summer to lay eggs that produce tent caterpillars next spring.

"That's about the only thing," she said. "Spraying doesn't control the population at all."

They might look like something out of a B horror movie, these soft and squishy caterpillars, but they don't bite or pose health hazards. Still, Albers says, it's hard not to get the willies.

"You think you can handle it and you get into situation where they're crawling on you," she said. "I've even been freaked out."

She said homeowners should pick their battles in the war on tent caterpillars.

"Figure out what you absolutely have to do something about to make you feel better about the situation," she said. "Is it your patio furniture? Is it your house? Be persistent. If it's sweeping them off or spraying, you have to be persistent. That's the basic thing, and you're just going to have to ignore the rest, and that's the hard part.

"You can get overwhelmed very easily."

• On the Web: dnr.state.mn.us/treecare/forest_health/ftc

This story includes material from The Associated Press.

Dokken reports on outdoors. Reach him at (701) 780-1148; (800) 477-6572, ext. 148; or send email to bdokken@gfherald.com .