What Is a Miller Moth?

Some people mark the passage of time by remembering what they did each year on their birthdays or Independence Day. For me, it’s the annual miller moth migration.

It usually starts with one or two moths who nestle around my door frame and accidentally flutter into the kitchen. Before long, there’s a whole cloud of them coming down the road, working their way into garages, under the hoods of cars and any other nook where they can seek shelter.

To me, the millers are a happy sight. They’re one of nature’s spectacular migrations, corresponding with other great events like the start of hiking and wildflower season in the mountains. But I’m the exception. Most people see them as a major annoyance.

Here’s what to know about miller moths and their migration, plus how to make peace with these little flyers.

What Is a Miller Moth?

WireStock/Getty Images

Millers are robust, drab-colored moths about the size of a quarter. They’re most common in the Great Plains and Rocky Mountains. They got their name from fine scales that fall off their wings, which resemble the dust covering the clothing of millers — those old-timers who turned grain into flour.

Miller moths are strong pollinators who play a key ecological role feeding birds, bats, spiders and bears, even grizzlies. Each moth contains only one-half of a calorie, but bears eagerly turn over rocks to find them, eating as many as 40,000 a day!

Miller Moth Migration

Miller moths begin their lives on the high plains as army cutworm caterpillars. After they pupate (i.e. turn into moths), they embark on a westward migration in search of flower nectar to feed on, finally ending up in the mountains.

For a few weeks between mid-May and early July, their route collides with the most populous cities in the region, like Denver and Colorado Springs. There they end up under our eaves, smashed on our windshields and blundering about our window panes.

We tend to see them as pests, but they’re actually just traveling through, trying to navigate our towns with lots of confusing unnatural lights so they can reach their millennia-old habitat. Miller moths also migrate the other way in the fall, but we usually don’t notice because by then so many of them have been eaten.

What Do Miller Moths Eat?

Adult miller moths feed on flower nectar. Their larvae (those cutworm caterpillars) eat a wide variety of vegetation, from broadleaf plants to grasses. Miller moths do not eat household food, fabric or furniture, which isn’t unusual. Out of 160,000 species of moths, only two eat our clothes.

What Damage Do Miller Moths Cause?

Not much. They may interrupt our sleep by bouncing around the bedroom ceiling at night. And they can leave spots on unfinished wood or drapes due to a slightly acidic fluid they excrete. But they don’t lay eggs or otherwise reproduce in a home. Plus, it’s OK if your pet eats them; they’re nutritious, not poisonous.

“Miller moths are harmless,” says Shiran Hershcovich, lepidopterist manager at Butterfly Pavilion in Westminster, Colorado. “As they migrate, the adult moths visit flowers without damaging gardens. In fact, as they pollinate, they provide benefit to outdoor spaces and gardens.”

How To Get Rid of Miller Moths

WireStock/Getty Images

The kindest way to remove them from your home is also the simplest — catch them in a cup or your hand and release them outside. Once outdoors, the moths will eventually move along to where they wanted to go in the first place.

Otherwise, you can vacuum them or attract them with a trap. But only trap them if they’re stuck indoors and you have no other option. To make a trap, hang a light bulb over a bucket containing a little soapy water, which the moths will eventually fall into.

Millers are also sensitive to noises like jingling keys or dog tags, rattling coins and crumpling pop cans, according to Colorado State University Extension. These cause them to fly erratically, probably because their sound frequencies resemble the echolocation of bats, one of their predators. Making these noises can cause the moths to take flight, speeding up the process of getting them in the trap.

As for dead miller moths, it’s better to toss them in the garden than the garbage so their nutrients don’t go to waste.

Note: Insecticides don’t work well for miller moths and can affect the health of important local pollinators like bees and butterflies. Avoid whenever possible.

Miller Moth Prevention

In preparation for miller moth season, make your home weather-tight, especially around windows, doors and anywhere else light can come through. Then once the moths arrive, turn off all unnecessary outdoor lights or replace them with yellow lights, which don’t attract millers.

Remember the moths seek dark and tight daytime shelter; that’s why they cluster around door jambs. So when opening doors, try to keep the moths from making a wrong turn into your house.

Your landscaping can also attract millers, especially lilacs, cherries, horse chestnut, raspberry and Russian olive. But of course, it’s probably not worth getting rid of your flowers and bushes just so the moths move on faster.

Sometimes the best prevention involves getting to know your foe, and realizing they can also be friends. “Approach moths with curiosity,” says Hershcovich. “Learn about the fascinating world of invertebrates in spaces like the Butterfly Pavilion.”