Posted 12 months ago
By Kevin Horn
Earlier this year a large population of army cutworm larvae was reported in western Nebraska. In the spring, cutworm larvae turn into moths that are commonly known as miller moths, and now the millers have begun emerging in parts of Nebraska.
One sign of the moths’ initial arrival is birds scattering about in the streets to chase down the succulent treats (the moths are attracted to street lights at night). What isn’t such a treat for humans is that the moths can invade homes, garages, and vehicles.
When disturbed, great clouds of moths can suddenly disperse, and often defecate as they disperse. While sometimes irritating, they cause little harm and are present in large number for only a few weeks. There is a return flight in the fall; however, their numbers are often much less.
Army cutworm moths or millers usually begin to appear in early to late May. The moths are generally gray or light brown with a wingspan of 1 1/2 to 2 inches. Each forewing is marked with spots, wavy lines, and other dark and light markings. Individual moths can vary considerably in their markings and can look similar to another species of moth (the western bean cutworm moth) that occurs later in the year.
The moths prefer to feed at night on the nectar of flowering shrubs and trees. This feeding does not harm the plants. As dawn approaches they congregate and may enter homes, garages, barns, and sheds in search of resting sites. Narrow cracks or crevices are preferred, but any protected area is suitable. If they are disturbed during the day, they will quickly escape and find new hiding places.
At dusk, the moths re-emerge and continue feeding on nectar or migrate to other areas. Some moths, however, may enter homes, where they become a nuisance. With the exception of occasionally staining curtains and other surfaces with their droppings, they cause little harm.
The great hoards of millers in the spring are a result of their migratory nature. Their numbers will depend on spring cutworm populations and environmental conditions. Moths emerging in Nebraska tend to remain in the area for two to three weeks, but may stay for up to six weeks or as long as local plants are flowering. Cool, wet conditions during this time will extend their stay. Hot, dry conditions will encourage them to move westward.
The moths will migrate westward to higher elevations as they follow the progression in the initiation of spring flowering plants. During this time, with the aid of easterly winds, moth concentrations can increase dramatically. When the last trees finish flowering (e.g. locusts and lindens) and temperatures increase in the high plains, the moths move to the Rocky Mountains. There they escape severe summer temperatures and find alpine flowers, their primary food source.
In September the moths once again return to the plains. Army cutworm moths are noticed throughout Nebraska from mid-September through October.
As they migrate eastward, they mate and lay eggs in barren or sparsely vegetated fields, especially winter wheat, alfalfa and grasslands. The eggs hatch within a few weeks and the larvae begin to feed.
Sidebar: Home Management of Millers
When millers emerge and begin to move westward in the spring, area residents have little recourse but to patiently await their departure. There are a few tactics, however, that can help lessen moth activity in and around homes:
If millers enter a house or other buildings, they can be swatted, vacuumed, or trapped. An insecticide application will have limited effectiveness, as it will only kill those that it contacts. The best solution is to simply keep doors and windows closed, keep porch lights off and patiently wait for these annoying migrants to move on.