Incoming! Radar lights up as 110km swarm of butterflies drifts across Colorado

A lacy, cloud-like pattern drifting across a Denver-area radar screen turned out to be a 110km-wide swarm of butterflies, forecasters say.

Paul Schlatter of the National Weather Service said he first thought flocks of birds were making the pattern he saw on the radar Tuesday, but the cloud was headed northwest with the wind, and migrating birds would be southbound in October.

He asked birdwatchers on social media what it might be, and by Wednesday had his answer: People reported seeing a loosely spaced net of painted lady butterflies drifting with the wind across the area.

Schlatter said the colours on the radar image are a result of the butterflies’ shape and direction, not their own colours.

Midwestern radar stations occasionally pick up butterflies, but Schlatter believes it’s a first for Denver.