Over the last week, homeowners in the Lake Superior Counties of Wisconsin have been reporting egg masses on the sides of buildings or under the eaves. These yellow to orange-colored egg masses are being deposited by variegated cutworm moths, primarily at night. Cutworms are a large group of lepidopteran insects that include the more common black cutworm. The variegated cutworm adults are moths that lay eggs on weeds (and buildings). The eggs hatch caterpillars that feed on herbaceous plants. After a few weeks of feeding the caterpillars pupate and another generation of moths is hatched. Variegated cutworms are a climbing cutworm with the caterpillars climbing into the plants to feed during the night and hiding in shade or in the soil during the day. The current flight of cutworm moths likely flew into the region from the South with the help of prevailing winds. Farmers in Oklahoma, for example, experienced high levels of variegated cutworms in April of this year. With most lepidopteran species there is a concentrated flight of adult moths, followed by egg-laying and hatching of the caterpillars from the eggs. How long this flight of moths will last is unknown, as a flight of this magnitude of variegated cutworms has not been seen in recent memory. However, like other lepidopteran insects this peak flight and egg-laying is likely to last for at least another week or two. To limit egg laying on houses, turn off outdoor lights.
The best option for homeowners at this point is to wash off the egg masses with a pressure washer or garden hose. What comes next is unknown. Eventually, the eggs will hatch, but it is unclear whether the caterpillars will become a problem. Homeowners are encouraged to monitor vegetables, flowers, and ornamental shrubs carefully over the coming weeks. If caterpillar feeding is observed on desirable garden or ornamental plants, it may be worth spraying the vegetation with an insecticide containing Bt, spinosad, or permethrin when the caterpillars are active. Insecticides are poisonous and can be harmful to people, pets, or beneficial insects. Always carefully read and follow the label of any insecticide. The South shore of Lake Superior is likely to see quite a bit of caterpillar activity this spring as eastern tent caterpillar and gypsy moth populations are currently high and the forest tent caterpillar population is building.
The following website links will provide you with additional information on Gypsy Moths, the Forest Tent Caterpillar, the Eastern Tent Caterpillar and the Black and Variegated Cutworm.