Check for signs of the gypsy moth this spring

As I write, my colleagues at the Washington Conservation District are out at the County Fairgrounds in Lake Elmo, handing out approximately 20,000 trees and more than 100 rain barrels, ordered during this year’s spring sale. Indeed, spring is a time when many of us look out the window into our yards and realize we aren’t quite satisfied with what we see. The nurseries will be humming in a few weeks as people get ready to plant new gardens or buy additional flowers for existing plantings. Some will be replacing trees and shrubs that were damaged by deer and rabbits over the winter. In addition to inspecting our yards for obvious damage, though, we should all be on the lookout for signs of gypsy moths. 

Ranked among America’s most destructive tree pests, the gypsy moth has caused millions of dollars in damage to forests as it has spread from New England to Wisconsin in recent decades. It is an invasive leaf-eating insect that can defoliate large sections of forest, especially oak, poplar, birch and willow. The pests are common in Wisconsin and are now threatening eastern Minnesota.  In fact, a statewide monitoring program, led by the Minnesota Department of Agriculture (MDA), found a localized infestation of gypsy moths last summer in an 844-acre section of the city of Grant along Keats Avenue just west of Stillwater and north of Highway 36.

Gypsy moth caterpillar

Female gypsy moths lay egg masses, containing 500-1000 eggs, on any available outdoor surface in late summer. The eggs remain dormant during the winter until they hatch in the spring as little fuzzy caterpillars, up to 2.5 inches long, with a two distinctive rows of spots down their backs. The first five pairs of spots, working from the head down, are blue, while the remaining six are red. Although they may look innocent at this stage, the gypsy moth caterpillars are extremely dangerous for trees. They feed for five to six weeks during late spring to mid-summer, during which time each caterpillar can eat up to nine square feet of leaves. Eventually, the caterpillars form cocoons in the mid to late summer, with adult gypsy moths emerging shortly thereafter.

Over the years, the Minnesota Department of Health has successfully treated dozens of gypsy moth infestations across eastern Minnesota from Grand Marais to Winona County.  In the Twin Cities, they successfully eliminated infestations in Minneapolis and Golden Valley in 2002, Edina in 2004, Brooklyn Park in 2006, and Minnetonka and Richfield in 2009.  These successful treatments help postpone the full-scale invasion of gypsy moth, saving local communities and homeowners money and protecting the health of the state’s forests. MDA plans to treat the area in Grant, as well as two other metro-area infestations, in May using a biological insecticide called Bacillus thuringiensis var. kurstaki, or Btk. Btk contains proteins from naturally-occurring bacteria, which become toxic when eaten by certain susceptible caterpillars like the gypsy moths and tent caterpillars. The insecticide is not dangerous for humans and other mammals.

If you find egg masses or caterpillars in your yard this spring and believe they may be from gypsy moths, note their exact location, take a digital photo if possible, and then call the “Arrest the Pest” hotline at 651-201-6684. If you travel to any infested areas within Wisconsin, be sure to check your vehicle for gypsy hitchhikers before returning and avoid bringing back firewood or logs that could harbor gypsy moth eggs.

More information about gypsy moths and MDA’s battle against these forest pests can be found on the department’s website at