Meteorologists depend on radar to help track weather patterns and dangerous conditions before they hit. Sometimes, though, they get caught off guard by what shows up.

A team of scientists for the National Weather Service in Boulder, Colorado got a little tripped up by what was showing up on their radar. The moving blip caught their attention, and at first they thought it was a flock of birds.

The large mass was 70 miles wide and was traveling through the region, but forecasters were stumped by which species it could have been. So, they put out a call through social media to see if any birdwatching folks could help to identify them.

Reponses poured in to share that it was a swarm of migrating butterflies! A group of painted lady butterflies to be exact. This particular migratory butterfly is known for flying up to 30 miles per hour when on the move and can travel long distances. That purple blob you see in this radar picture that resembles a cloud is due to them flying together with the wind current.

Often mistaken for monarch butterflies, painted ladies are smaller and have brown coloring on both sides of their wings. The creatures are found all over the world. It’s not uncommon for hundreds of thousands of them to flock together during a migration, and sometimes, their numbers can reach into the millions.

Typically, the painted lady will lay eggs along the way to their fall destination, allowing for another generation to repopulate by spring. Their remarkable stamina helps them to travel over 1,000 miles in their short life spans.

Though their migratory patterns are unpredictable, they don’t favor the cold and tend to head south or southwest when temperatures start to drop. Colorado State University told Denver’s Fox 31:

“During winter, they vacate most of the US remaining active only in parts of the extreme southwestern states and northwestern Mexico, particularly Baja, Mexico.”

Experts at the weather center noted that it’s rare for an insect migration to register on their radar systems in the same manner as a large bird flock. Between September and now, Colorado and other western states are being treated to a flush of the insects as they head for warmer, food-rich pastures.

People are excited about seeing them in droves in their yards and other flowery environments as they stop to drink nectar. Though the painted lady is one of the most widely distributed and common butterflies in the world, to see this many at one time is a sight to behold. Click on the clip below to get a glimpse of the beautiful insects!

Unfortunately, the life span of the painted lady is only two weeks. It’s new generations of them that are seen when they migrate in between seasons. Warmer temperatures help to keep them well-fed and mating over and over. So, if you happen to see a battalion of painted ladies near you, cheer them on!

Do you live a region where you get to see swarms of painted lady butterflies? Have you ever witnessed a large insect migration?


U.S. Fish & Wildlife Service