Miller Banner Light
Manases Blakemore
Army cutworm moths have a wing span of 1.5 to 2 inches. It is generally gray or light brown with wavy dark and light markings on the wings. The wing patterns of the moths are variable in color and markings, but all have a distinctive kidney-shaped marking on the forewing.
Miller moths are the migrating adult stage of the army cutworm. In eastern Colorado, spring flights move westward, originating from moths that developed across eastern Colorado and border areas of Wyoming, Nebraska, Kansas, and Oklahoma where army cutworm also occurs.
A likely explanation for the migration is that it allows the moths a reliable source of summer flowers. Flowers provide nectar which the moths use for food. In addition, the cooler temperatures of the higher elevations may be less stressful to the moths, allowing them to conserve energy and live longer.
During outbreak years, miller moth flights typically last five to six weeks, generally starting between mid-May and early June. However, they tend to cause most nuisance problems for only two to three weeks.
The return flights (mountains to the plains) in early fall usually span a shorter period of time, typically beginning in the latter half of September. However, since the majority of moths die during the summer the return flight is less obvious.
The number of miller moths in late spring is primarily related to the number of army cutworm caterpillars which occurred earlier in the season. Outbreaks of the army cutworm are usually followed by large flights of miller moths.
Many things influence cutworm outbreaks. Wet weather and extremely cold winter conditions may kill many of the caterpillars. The effectiveness of natural enemies, such as ground beetles and parasitic wasps, help regulate cutworm populations. Plowing fields where cutworms develop kills many, as does tilling gardens.
Miller moths may concentrate around buildings more intensively during some years. The presence of flowering plants and local humidity conditions are suspected as being important in concentrations of miller moths. This effect is seen particularly during drought years when there are few natural sources of flowering plants at lower elevations. The presence of certain highly favored flowering plants, notably Russian olive, is frequently associated with localized nuisance problems.
The caterpillar stage of the army cutworm is sometimes an important crop pest in the spring. For example, during outbreak years thousands of acres of alfalfa, winter wheat, and other crops are treated with insecticides for army cutworm control (See fact sheets 5.577, Caterpillars in Small Grains and 5.565, Caterpillars in Field Crops: III.). Army cutworms are also common early season pests of gardens and feed on lawn grasses along with sod webworms and other cutworms.
When large numbers die in a home there may be a small odor problem (due to the fat in their bodies turning rancid). Also, unless they are cleaned out, old moths may serve as food for carpet beetles (See fact sheet 5.549, Carpet Beetles.) and other household scavengers. These secondary insects may become problems in subsequent years.
Miller moths also may spot drapes or other surfaces, such as unfinished wood because they excrete fluid for most of their adult life. This product is slightly acidic and is sprayed by the moth. Presumably the purpose of this is defensive, although it is not particularly irritating.
Probably the greatest damage created by millers is the lost sleep resulting from their flying about the room and the needless worry that they may reproduce in the home and cause harm to household furnishings.
One commonly observed phenomenon involving birds is swallows concentrating at intersections where they feed on miller moths. (House sparrows and other birds also are found at these sites, feeding on wounded moths.) This likely occurs because many miller moths seek shelter in automobiles and emerge while the cars are idling at stop lights. Furthermore, many moths are released as drivers open vehicle windows at intersections to let the moths escape.
Before miller moth migrations, seal any obvious openings, particularly around windows and doors. Also reduce lighting at night in and around the home during flights. This includes turning off all unnecessary lights or substituting non-attractive yellow lights.
Once in the home, the best way to remove the moths is to swat or vacuum them, or attract them to traps. An easy trap to make is to suspend a light bulb over a bucket partially filled with soapy water. Moths attracted to the light often will fall into the water and be killed. (If this is attempted some wetting agent, such as soap or detergent, must be added or many moths will escape. Also, there are obvious dangers when bringing water and electrical equipment in close proximity and great care should be given to the situation. This includes use of a GFI receptacle for safety.)
Army cutworm moths are very sensitive to certain noises, making erratic flying movements in response. Among the sounds which elicit greatest response are jingling keys, dog tags, rattling coins, and crumpled pop cans. The likely reason for this is that certain sound frequencies are produced to which the moths are sensitive. Many cutworm moths make evasive movements in response to frequencies used by bats during echolocation of prey. Since bats are an important predator of night flying moths, rapid evasive movements are a means of protection. Regardless, jingling keys or making similar noises can disturb many of the moths in the home causing them to seek shelter and can sometimes dramatically speed the capture rate when using the soapy water trap.
Insecticides have little or no place in controlling millers. The moths are not very susceptible to insecticides. Furthermore, any moths killed will be rapidly replaced by new moths migrating into the area nightly.
The most common moth found in Colorado homes is the Indian meal moth. Adults are much smaller than the miller moth, about 1/2 inch, is yellow brown with a dark tip on the wing. The caterpillars of the Indian meal moth develop in various cereal products, nuts, dried flowers, and other stored foods. Information on the Indian meal moth can be found in fact sheet 5.598, Indian Meal Moth.
Clothes moths are very rare in Colorado, but can occur when infested woolen items are introduced into a home. It is a very pale colored moth even smaller than the Indian meal moth. They are rarely observed flying and do so only when dark.
Colorado State University, U.S. Department of Agriculture, and Colorado counties cooperating. Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.
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