The Miller Moth Returns - UNL CropWatch, May 3, 2013
May 3, 2013
Early this year we mentioned the large population of army cutworm larvae that had been reported in western Nebraska. Those cutworm larvae turn into moths that are commonly known as “miller moths” in the spring.
Spring miller moths have begun their emergence in some parts of Nebraska. The moth’s initial arrival can be noted by the presence of 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 us) 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, there 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 (Figure 1), with a wingspan of 1 1/2 to 2 inches. Each forewing is marked with spots, wavy lines, and other dark and light markings. 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.
Just a Stop on Their Migration
The great hoards of millers noticed in the spring are a result of the migratory nature of these animals. The severity of moth aggregation during the migration 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 average temperatures increase in the high plains, the moths move to the Rocky Mountains.
This migration allows the moths to escape severe summer temperatures and find alpine flowers, their primary food source. When the alpine summer comes to a close in September, the moths once again take flight, returning 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.