Large Moths in Colorado: Quick Guide on Dealing with These Visitors

Large moths can be quite the sight in Colorado, especially during their peak months.

One such example is the miller moth, which can become a nuisance for some residents as they migrate from the plains to the mountains in late spring.

These moths are the adult stage of the army cutworm, scientifically named Euxoa auxiliaris.

Though miller moths may be bothersome, they do not breed indoors, preferring to live outside, and usually die within a few days when trapped in homes or cars.

Source: xpdaCC BY-SA 4.0, via Wikimedia Commons

But army cutworm moths are not the only large moths with an impressive appearance in Colorado.

The state is also home to large caterpillars known as hornworms, which transform into the strikingly beautiful hummingbird moths.

As a resident or visitor of Colorado, understanding and coexisting with these moths as part of the region’s diverse wildlife is an opportunity to appreciate the state’s rich ecosystem.

Should you encounter moths in your home or garden, taking a few simple steps, such as utilizing screens and limiting exterior lighting, can help reduce their presence and maintain balance in your immediate environment.

Understanding Large Moths in Colorado

Miller Moths and Their Migration

Miller moths, specifically the army cutworm moth, are a common species found in Colorado.

They migrate annually from the plains to the mountains in late spring, which can sometimes lead to them becoming a nuisance in homes.

File:Euxoa auxiliaris P1110068a.jpg
Large Moths in Colorado
Source: xpdaCC BY-SA 4.0, via Wikimedia Commons

Relationship to Colorado’s Ecosystem

  • Pollinators: Miller moths serve as important pollinators for many Colorado plants, contributing to a healthy ecosystem.
  • Prey for wildlife: They are a food source for various native birds and bears during their migration.
  • Moon-driven migration: It’s believed that miller moth migrations might be influenced by the moon, which affects the behavior of other nocturnal insects as well.

Distinctive Moth Traits

  • Euxoa auxiliaris: The scientific name for miller moths.
  • Size: Adult moths are about 1 inch long.
  • Color: They have variable colors, ranging from shades of brown to gray.

Comparison of Moth Traits:

TraitMiller MothOther Moths
Size1 inch longVaries
ColorBrown to grayVaries
MigrationYes (Colorado)Varies

Night Feeding Habits

As nocturnal creatures, miller moths are most active at night. They feed on nectar from various plants in Colorado, making them crucial for the local ecosystem.

Moths and Human Interaction

Are Miller Moths Harmful?

  • Miller moths are harmless to humans and pets.
  • They are mainly a nuisance when they enter homes and vehicles.

Reducing Miller Moth Nuisance

Some steps to prevent Miller Moth inconvenience:

  1. Seal gaps around windows and doors to prevent entry.
  2. Reduce outdoor lighting to minimize moth attraction.
  3. Switch off lights or use yellow “bug lights” on porches.

Moths and Artificial Light

  • Miller Moths are attracted to light.
  • Dimming or turning off artificial lights, like porch lights, can help reduce their presence.
Light SourceMoth Attraction Level
Bright whiteHigh

Dealing with Moths Indoors

Here’s how to manage moths inside your home:

  • Gently swatting rather than crushing moths is a cleaner way to control them.
  • Put a container with soapy water under the artificial light to trap moths.
  • Vacuuming can effectively get rid of moths in small spaces.
Source: xpdaCC BY-SA 4.0, via Wikimedia Commons

Moths and the Environment

Ecological Roles in Colorado

Miller moths are a common type of moth found in Colorado, particularly during their annual migration from the eastern plains to the mountains in late spring 1.

They play essential ecological roles, including functioning as pollinators and a food source for various animals.

Pollinator and Food Source

Miller moths contribute to pollination as they search for nectar in gardens and flowers 2.

Some examples of plants that benefit from moth pollination are evening primrose and night-blooming flowers.

Additionally, they serve as a valuable food source for many birds and bats, as they can rely on them as a stable supply of nutrition.

Predators of Miller Moths

There are several predators of miller moths:

Birds: One of the primary predators of Miller moths are birds. Species such as swallows, nighthawks, and robins are known to feed heavily on moths during their migration.

The abundance of Miller moths during their peak months provides a rich food source, aiding birds, especially during their breeding seasons.

Bats: Bats are nocturnal hunters, and moths are a staple in their diet. The echolocation abilities of bats allow them to detect and capture Miller moths efficiently during the night.

Spiders: Spiders, with their intricately woven webs, often capture Miller moths. Orb-weaving spiders, in particular, are adept at trapping these moths, making them a significant predator.

Rodents: Ground-dwelling rodents such as mice might feed on moths when they are available in abundance, especially if the moths are resting or have fallen to the ground.

Bears: In some regions, especially during the Miller moth migration in Colorado, bears have been observed feeding on them.

The moths provide a source of fat, making them an attractive, albeit unusual, food choice for bears.

Insects and Parasites: Certain insects, like predatory beetles, might prey on Miller moth larvae.

Additionally, parasitic wasps and flies can lay their eggs in or on the moth larvae, with their offspring consuming the host.

Source: xpdaCC BY-SA 4.0, via Wikimedia Commons

Climate Impact on Moth Populations

Colorado State University entomologists believe increased moth populations in some years may be due to a climate-driven seasonal surge 3.

Climate change affects the life cycles and distribution of moths across the state, leading to higher moth numbers and increased impact on gardens and flowers.

Climate FactorImpact on Moth Populations
Warmer temperaturesExtension of breeding season
DroughtMay lead to food stress for moth larvae
Extreme weather eventsCan disrupt moth migrations

Protecting Moth Species

Protecting moth species is essential for maintaining a balanced ecosystem. Here are some steps to help protect them:

  • Promote native plants: Planting native flowers in your garden provides moths and other pollinators with a natural habitat and nectar source.
  • Limit light pollution: Reducing unnecessary outdoor lighting can help moths navigate and reduce disorientation during their migrations.
  • Avoid harmful pesticides: Utilizing eco-friendly pest control methods prevents harming moth populations and their natural predators.

Encouraging Moth-Friendly Habits

Moth-Compatible Gardening

Create a welcoming environment for moths in your garden by planting native flowers. Incorporating plants such as:

  • White and cream-colored flowers that bloom at night
  • Seasonal blooming flowers to provide food sources throughout the year
  • Colorado-specific plants such as columbine, penstemon, and blanket flower

In addition to native flowers, reducing the use of irrigated lawns can promote a healthier ecosystem for moths and other wildlife.

Source: xpdaCC BY-SA 4.0, via Wikimedia Commons

Reducing Light Pollution

Moths, like other nocturnal creatures, rely on moon and starlight for navigation.

Artificial lights can disrupt their natural behavior. To minimize light pollution, consider:

  • Switching off outdoor lights when not needed
  • Using motion-activated lights
  • Opting for amber or red light bulbs, which have less impact on moth behavior

Reducing the use of reading lamps and bedroom window lights during miller moth season in Colorado can also help.

Coexisting with Moths

While moths may seem like a nuisance during their seasonal surge, it’s important to remember their ecological role. They:

  • Act as pollinators for a variety of plants
  • Serve as a food source for migratory birds and other wildlife

During moth season, use a vacuum to clean up any moths inside your home instead of using harmful chemicals.

By implementing these moth-friendly practices, you can both support moths and enjoy the benefits they bring to Colorado’s ecosystem.


In the vibrant ecosystem of Colorado, the Miller moth stands out not just for its seasonal presence but also for its ecological significance.

As the adult stage of the army cutworm, these moths migrate annually, serving as vital pollinators and a crucial food source for various predators.

While their nocturnal habits and attraction to light can make them a nuisance in homes, understanding their role and importance, from pollination to supporting wildlife, fosters a deeper appreciation for these winged wonders.




  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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