Butterfly swarm shows up on Denver radar system
Image copyright NWS Image caption Birds (left) leave a different radar signature to butterflies
A colourful, shimmering spectacle detected by satellites over the US state of Colorado has been identified as swarms of migrating butterflies.
Scientists at the National Weather Service (NWS) first mistook the orange radar blob for birds and had asked the public to help identifying the species.
They later established that the 70-mile wide (110km) mass was a kaleidoscope of Painted Lady butterflies.
Forecasters say it is uncommon for flying insects to be detected by radar.
“We hadn’t seen a signature like that in a while,” said NWS meteorologist Paul Schlatter, who first spotted the radar blip.
Image copyright USFWS Image caption The Painted Lady is often mistaken for the monarch butterfly
“We detect migrating birds all the time, but they were flying north to south,” he told CBS News, explaining that this direction of travel would be unusual for migratory birds for the time of year.
So he put the question to Twitter, asking for help determining the bird species.
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Skip Twitter post by @NWSBoulder
Look at what's flying into Denver! Radar from last hour showing what we believe to be birds. Any bird experts know what kind? #ornithology pic.twitter.com/EAqzdMwpFU
— NWS Boulder (@NWSBoulder) October 3, 2017 Report
End of Twitter post by @NWSBoulder
Almost every response he received was the same: “Butterflies”.
“Migrating butterflies in high quantities explains it”, he later wrote on the NWS Boulder Twitter account.
Namely the three-inch long Painted Lady butterfly, which has descended in clouds on the Denver area in recent weeks.
The species, commonly mistaken for monarch butterflies, are found across the continental United States, and travel to northern Mexico and the US southwest during colder months.
They are known to follow wind patterns, and can glide hundreds of miles each day.
