We had tons of army cutworm larvae in many of our wheat and alfalfa fields this spring. I have never used the word tons when trying to describe a quantity of insects, but here is some math. We recently conducted an insecticide efficacy trial on these larvae, and they averaged 7 per square foot. An acre would have 304,920, and a 50-acre field would have 15,246,000. We have many, many wheat fields that are infested this year. The larvae are now entering the pupal stage and will soon emerge as adults and invade our homes and structures.
Army cutworm larvae from two plots in the efficacy trial.
They prefer to fly at night and seek shelter in the day, which is why you will get up one morning and find your porch covered, and more moths in the house if it is not sealed up well. Don’t leave your truck windows down either. Some people say that a bowl of water and a little dish soap can be left under a porch light. The moths come to the light and contact the water where the dish soap has eliminated the surface tension so the moths sink and drown. This is true, but it won’t really reduce the number of moths to any degree, although the revenge factor might make you feel better. Revenge might be on your mind because the two biggest complaints about the moths are that they keep people from sleeping because of all of that flying around in the bedroom while they are trying exit the house, and because the oils from their bodies stain draperies and furniture.
An army cutworm moth.
“Miller moth” is a generic term that refers to several moth species that fly in large numbers and create a nuisance. Here on the High Plains the Millers are usually the army cutworm. The adults that fly in a few weeks will spend some time feeding on plant nectar, making us even crazier than we already are under this COVID-19 isolation, and then they will begin their long migration to the Rocky Mountains where they will spend the summer annoying people there. The bears won’t mind though because Miller moths are a delicious treat for them and they are known to eat up to 40,000 per day, which provides approximately 20,000 calories. (Our insectivorous bats and birds will have a good time in the next month or so as well.)
As summer wanes the surviving moths will begin migrating back to Nebraska, Kansas, Oklahoma and the Texas Panhandle. Each female will lay as many as 1,000 eggs in the fall on wheat, alfalfa, various weeds and even turfgrass. The eggs will hatch and the resulting larvae will overwinter. Larval development in the spring is slow because it is cold, and insect metabolism is very slow when it is cold. Eventually though they will become fully grown, pupate, and next year’s moths will emerge.
