A mothy situation

Overrun with moths? Blame the worms
Katherine Sears Managing Editor
Saturday, July 9, 2022
A mothy situation

Miller moths congregate in a windowsill of a home. The insect feeds at night and will hide in cracks or crevices during the day. Photo courtesy of MSU Extension

A mothy situation

The Army Cutworm Moth (Euxoa auxiliaris) is a fairly large (40 - 45 mm wingspan) grey-brown moth. It is one of the largest moths in the Euxoa genus. Montana Field Guide

A mothy situation

An army cutworm larva rests on a leaf. Cutworm larvae will hatch, resulting in the “miller” moth found inside homes this time of year. Montana Field Guide

If you think you’re having a problem with moths this year, you’re not alone. According to MSU Extension, Montana and the surrounding regions are currently observing large numbers of “miller” moths congregating in or near buildings at night where they are attracted to light sources.

While a moth here or there may be common during the summer months, the past few weeks have yielded large hatches of the brown, winged insects.

“They kind of come and go in cycles,” said Judith Basin Extension Agent Katie Hatelid. “I think it has something to do with how cool and wet the spring was, and then the big hatch came all at once instead of being spread out.”

According to MSU Extension, outbreaks tend to cycle periodically, remaining low for several years, then increasing and peaking for two to three years. Miller moths are the adult stage of a cutworm, Euxoa auxiliaris.

“They generally come from some sort of worm,” said Hatelid. “Those are usually army worms or cutworms.”

The worms lay their eggs during the fall season and the larvae overwinter. The larval caterpillar stage feeds on a variety of plants and crops during the spring season.

“They can cause damage in the worm form,” said Hatelid. “That’s where the crop damage happens, like winter wheat and spring wheat.”

Hatelid said she didn’t receive many reports of worm damage this spring, though areas around Great Falls reported some damage.

“If you notice a lot of the worm form, you can take action and spray,” said Hatelid. “You’ll see them cocoon on currant or chokecherry bushes – they’re an inch or less in length in their worm form.”

Now, in the early summer, the emerging adult stage migrates from the plains to higher elevations in the mountains.

This means they may find their way into homes and other buildings, which can be very annoying, but not harmful.

“In the miller form, they don’t hurt anything, other than the nuisance they cause by getting into your home and being everywhere,” said Hatelid.

According to Extension, they also feed almost exclusively at night. During the day, they like to hide in small cracks and crevices, which can be in homes, under cars, and other areas around the home. They don’t reproduce or feed on anything within the home.

While you might not be able to completely keep them out of your house, there are a few steps homeowners can take to mitigate the moth populations inside their home.

Moths are attracted to lights so some suggestions include turning off outdoor lights, sealing doors and windows, and leaving an outbuilding lighted to divert them and considering yellow insect lights as they are less attractive. Vacuum up moths when they are inside the home. Jingle keys or coins, as they don’t like erratic noises. Insecticides are rarely effective against the moths, as they are not very susceptible to them.

Hatelid also suggests signing up for MSU Extension Ag and Urban alerts for more timely information on entomology and horticulture. You can sign up at urbanipm.montana.edu/