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Winter Cutworm

Jeffrey Hahn, Extension Professor and Asst. Extension Entomologist

Marge Kelley

Photo 1: Winter cutworm
There have been a number of reports this winter of caterpillars active on top of the snow. This mystery caterpillar is an exotic moth known as Noctua pronuba, commonly called the winter cutworm or (large) yellow underwing. The first report this season came from Itasca county in December. Then on New Years day, after we had a light snowfall, there were several reports of this insect in Washington county in the eastern Twin Cities area (note: there were also a number of reports across the border in northeast Wisconsin). One person said they found about 30 of these caterpillars while another said they saw as many as 60 - 70 at a time.

There is a precedent to seeing insects outdoors during the winter. Insects, including snow flea, snow scorpionfly, and small winter stonefly, are know to tolerate colder temperatures and can be found on top of the snow during winter. Now we can add winter cutworm to this list.

This caterpillar overwinters as a large larva. It has a smooth, hairless body and can be as large as three inches when fully grown. It is colored light to dark brown with a series of black dashes running down its back. It also has two black bracket-like markings on its head. As an adult moth, it has brownish forewings and bright orangish yellow hind wings with a black band near the margin of the wing.

Originally from Europe, winter cutworms were first found in North America in Nova Scotia in 1979. They are now generally distributed throughout the northeastern U.S. They are also found in the upper Midwest as well as a variety of other states, even California. They were first noted in Minnesota sometime in the late 1990's from moths collected at black light traps in Lamberton (in Redwood county in southwest Minnesota). It is likely there were present in other counties at that time and they are probably now generally distributed throughout the state. Interestingly, this is the first time that these caterpillars have been reported during the winter.

This insect feeds on a wide variety of agricultural and garden plants. Despite the fact that winter cutworm has been in Minnesota for 12 - 14 years, it has not been reported as a problem in agricultural fields. It is possible for home gardeners to find this insect but it is generally not expected to be a significant problem. Look for them right away in the spring and then again during mid to late summer and into the fall. If you do find winter cutworms, just treat them like any other cutworm.
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