Warmer weather across Colorado means it’s time to prepare for the annual influx of migrating miller moths. Soon, the dusty pollinators will be hovering around city street lights and sampling Front Range flowers on their journey to the mountains.
Miller moths, infamous in Denver for their large numbers and ability to find their way into homes, are critical for Colorado’s environment, Butterfly Pavilion lepidopterist and entomologist Shiran Hershcovich said.
As they travel from one plant to the next, transferring pollen while following the blooms across the state, moths help sustain Colorado’s environment, Hershcovich said.
“As they come into our spaces, just approach them with curiosity and respect,” she said. “They’re not coming into our living rooms, we’ve built our home in theirs.”
When is miller moth season in Colorado?
Miller moths typically swarm across Colorado from mid-May to mid-June, Hershcovich said.
Moths metamorphose from army cutworm caterpillars on the Great Plains in March and take off for western Colorado’s mountains in late spring, making pit stops on the Front Range during their journey, according to the Colorado State University Extension.
The moths come in waves as they emerge from their cocoons, said Genevieve Anderegg, assistant collections manager of invertebrate zoology at the Denver Museum of Nature and Science.
They travel west across the state for the cooler weather and to feed on the vast pollen and nectar that Colorado’s diverse environments offer, Anderegg said. They do the same thing on the other side of the mountain, but the population is smaller and less noticeable, she said.
The number of miller moths can vary dramatically each year and is largely unpredictable, Hershcovich said.
“Even though they visit our backyards each year, we know next to nothing about them,” Hershcovich said. “They’re so essential to life as we know it, but they’ve only recently begun to gain visibility in terms of research.”
The climate and the number of flowers in bloom have the biggest impact on the moth population.
How long do miller moths live?
Miller moths live about a year — just long enough to emerge from their cocoons on the Great Plains, migrate west to Colorado’s mountains and return to the grasslands in the fall to lay their eggs, Anderegg said. That is, if they don’t die during the migration.
The moths get confused by urban lights and often end up finding their way into Colorado homes, Hershcovich said, adding that miller moths use light from celestial objects like stars and the moon to orient themselves.
Once the moths start to appear in Denver, depending on the year and weather conditions, the peak will last from two to four weeks, Hershcovich said.
How can people control the number of miller moths in their home?
To prevent miller moths from making a home inside human spaces, Coloradans should seal any obvious openings, especially around windows and doors; reduce the number of lights in and around the home; or substitute yellow lights, according to the CSU Extension.
Miller moths may concentrate around buildings with more plants and increased humidity, the CSU Extension’s article stated. This effect is seen particularly during drought years when there are fewer flowering plants at lower elevations.
If they do make it inside, residents should carry them outside in a cup or their hands, Hershcovich said.
What happens if your pet eats a moth (or several dozen)?
“Miller moths are not dangerous in any way to us, our pets or our kids,” Hershcovich said. “They’re not venomous or poisonous.”
Many animals in Colorado — including birds, lizards and bears — rely on the moth population for food and as a key source of protein, she said.
“Your cat could eat cupfuls of moths and still be safe,” she said. “Honestly, the moths have the short end of the stick on this one.”
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