There are thousands of invasive species in the U.S. An exact number of these animals, plants and insects is unknown but, the U.S. Fish and Wildlife Service research suggests there are about 4,300 invasive species in the country.

One found in Wisconsin and Minnesota is the gypsy moth.

Arborist Tyler Hesseltine explained to the Republican Eagle that one of the threats of gypsy moth caterpillars is that they eat a variety of trees.

“We’re not worried about losing just the elm trees or just the ash trees,” explained Hesseltine. He added that this “makes it more concerning than something that focuses on a targeted plant.”

This moth was introduced to U.S. ecosystems between 1868 and 1869. A Smithsonian article explains that Leopold Trouvelot, an amateur lepidopterist living in Medford, Mass., had more than one million gypsy moth caterpillars in his backyard. Several escaped and about 10 years later the trees in Trouvelot’s neighborhood were severely defoliated. These escaped moths and their descendants began moving west.

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Along with being a threat due to the consumption of numerous trees, gypsy moths can be difficult to eradicate.

“The gypsy moth has special methods of dispersal. The young larvae have hairs with small air pockets that create buoyancy, allowing them to travel great distances when the wind is strong. They have been found as high as 2,000 feet in the air, and are known to travel five miles a day by this method,” the Smithsonian’s website states.

The moths are also “expert hitchhikers” according to the Minnesota Department of Agriculture. Female gypsy moths will lay eggs in mass, anywhere from 500 to 1,000 eggs according to Hesseltine. Usually the eggs are placed on solid surfaces such as cars, mobile homes, outdoor furniture, firewood and trailers.

Examples of gypsy moth egg sacks. Photo provided by the Wisconsin Department of Agriculture, Trade and Consumer Protection.
Examples of gypsy moth egg sacks. Photo provided by the Wisconsin Department of Agriculture, Trade and Consumer Protection.

Because of the moth's ability to hitchhike, numerous northeastern states have travel quarantines on items that are commonly used as nurseries for moth eggs. Central and eastern Wisconsin have these restrictions, as do Cook and Lake counties, the two largest counties in Minnesota.

“Quarantine violations occur when companies or individuals transport regulated articles out of the quarantined area without appropriate documentation and can result in civil or criminal penalties. Entities that regularly move regulated articles can continue to do so if they are operating under a compliance agreement,” the Minnesota Department of Agriculture website states.

While the gypsy moth has not been eradicated in the U.S., its spread has been limited. Hesseltine explained that he was surprised to learn that the moths were first introduced to the U.S. around 1869, stating that he was impressed by the control of gypsy moths.

There are a variety of natural and human made methods to decrease the gypsy moth population. Hesseltine listed cold weather, woodpecker predation of eggs over winter and individuals removing egg sacks that they find and destroying them before the larvae hatch.

“But really it's our management strategies that control the amount from year to year,” Hesseltine said.

Gypsy moths are targeted during the larval stage when they do not have eggs to help protect them and before they reach adulthood they begin laying eggs. The management strategy is a microbial insecticide, which is spread in areas where gypsy moth populations have been discovered.

The Minnesota DNR’s website states that “Bt products are considered nontoxic to humans, animals, fish, plants, other insects and microorganisms. Bt is highly selective; it only kills caterpillars of moths and butterflies. Bt will not contaminate groundwater because it degrades rapidly and becomes a natural component of the soil.”

Now, the Wisconsin Department of Agriculture, Trade and Consumer Protection is preparing for a second phase of gypsy moth treatments. This step focuses on adult male moths. Planes will apply a mating disruptor that will prevent male gypsy moths from finding female moths. This step will be done in 15 Wisconsin counties.

Hesseltine explained to the Republican Eagle that while gypsy moth management is still important, it is not always top of mind for residents in Minnesota and Wisconsin.

“Since we know that gypsy moths have been around for so long we’re a little desensitized to it,” said Hesseltine. He added, “It’s actually something we can’t take our eye off of.”


Invasive species: an organism that causes harm (which can be ecological and/or economic) in an environment to which it is not native.

Lepidopterist: a specialist of lepidopterology, which is a branch of entomology that focuses on butterflies, moths and skippers.

Larvae: The wingless and immature form that hatches from an egg. The next stage for these organisms is transforming into a pupa, which is a cocoon for moths.

Defoliate: To remove leaves from trees before they would fall naturally.

Bt: Bacillus thuringiensis, or the naturally occurring bacteria in many sprays used to kill gypsy moth caterpillars.