Radar Picks Up Massive Butterfly Migration

Painted Lady butterfly on a flower bloom
The painted lady butterfly, commonly confused with the monarch, migrates each spring and fall in response to the changing seasons.

novofotoo / Flickr

In October 2017, Denver meteorologists monitoring radar spotted unusual 100-mile-wide, red-and-purple blotches moving into the region. The bizarre patterns, which appeared to follow the direction of the wind, had all the appearances of tight bird migration. Nevertheless, the National Weather Service team thought a bit of crowdsourcing could help solve the puzzle and posted the radar signature on Twitter.

After many helpful responses, it was determined that the radar had captured a rare butterfly migration.

The insect responsible for this rare signature is the painted lady butterfly. Often confused with the monarch butterfly, the painted lady migrates in the fall from states like Colorado to warmer locales in the Southwest. Thanks to an earlier-than-usual spring and consistent rainfall, the population of painted ladies has exploded.

"I have been getting phone calls from people all over the Front Range in many different counties," Butterfly Pavilion lepidopterist Sarah Garrett told the Denver Post. "Last week, I spoke to folks in North Dakota and South Dakota who have seen them. They are making their way progressively through these Western states."

A beautiful sight from any angle

So what does a butterfly migration look like from the ground? Andrew Warren captured this video of a swarm of painted ladies in Douglas County, Colorado, last week.

In addition to the painted lady, the annual fall monarch migration is also underway. Last week, a town in New Jersey made the news after scores of monarchs on their way to Mexico decided to make a pit stop in a local cherry tree. Residents in Texas are also preparing for clouds of the beautiful orange-and-black insects to fly through what's known as the "Texas Funnel," an ancient migratory route more than 300 miles wide that cuts through the center of the state. Even schools are getting in on the fun of tagging and releasing young butterflies on their journey south.