VIDEO: Huge butterfly swarm on radar confuses weather analysts

A swarm of butterflies migrating over Denver, Colorado was so large that meteorologists studying the weather radar thought they were birds.

After scientists at the National Weather Service detected a 110km mass of flying creatures, they requested help from social media to identify the species responsible. 

However, the replies they received were not what they were expecting.

"Could it be butterflies? Butterflies EVERYWHERE in #Denver!" wrote one Denver local.

"Those are painted-lady butterflies," wrote another.

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Sure enough, Denver locals had been inundated with a descending kaleidoscope of painted lady butterflies over recent weeks, which often aren't picked up on radar.

National Weather Service staff, a little confused by all the butterfly responses, then able to confirm what was seen on their radar images via Twitter.

"YES! This signature is butterflies, rarely seen on our radar'," they wrote.

The species can glide hundreds of kilometres each day and follow wind patterns down to the US southwest in colder months, the opposite direction of migrating birds.

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One insect expert, Andrew D Warren, captured video of the invasion in a nearby area which can be viewed above or here.