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Annual miller moth migration off to early start in southern Colorado

Dr. Whitney Cranshaw, CSU Entomologist
Dr. Whitney Cranshaw, CSU Entomologist(KKTV)
Published: May. 14, 2020 at 8:39 AM MDT
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Whether you like them or not, miller moths are a spring tradition in Colorado. They're already invading homes or hanging out in yards across Colorado Springs and Pueblo.

This year's migration is happening earlier than usual. The moths typically fly from the eastern plains to the mountains for the summer starting in late May. Some of the first moths were spotted at the beginning of the month.

"The migration of the Army cutworm across the eastern plains to the mountains is a unique kind of event," said CSU Entomologist Dr. Whitney Cranshaw.

Cranshaw has been watching the annual miller moth migration for 35 years. He isn't sure why the moths are getting an earlier start this year, but he said this will be the first substantial flight since 2016.

There are two reasons for this. First, Cranshaw said there have been higher numbers of the Army cutworm reported on the eastern plains. The caterpillar is the immature form of the miller moth. He also said due to lower moisture in the fall, winter and spring, there aren't as many flowering plants to attract the moths on their way to the high country.

That means the moths will concentrate in areas where there are more flowers, like in local yards.

"That's usually irrigated landscapes, people's yards," said Cranshaw. "So, more of them will be in people's yards than there were last year when they were spread all over because everything was blooming."

The actual number of miller moths flying across the Front Range will be about average in 2020, but it may seem like more because there were below average numbers the past few years.

"For someone who has just recently moved here, they've never really experienced this," Cranshaw said. "The last four years have been extraordinarily low numbers."

The good news for anyone who cringes at the sign of a moth: because the miller moth migration is starting earlier, it will also likely end earlier. It usually lasts up to six weeks.

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