What was thought to be a flock of birds caught on the NWS Boulder, Colo., weather radar turned out to be a giant swarm of butterflies.

After a considerable amount of speculation along with plenty of investigation, it turned out what was appearing on the radar wasn't birds but an enormous flock of migrating butterflies.

The most important clue to what was happening came from residents in the area who said they were seeing a lot of butterflies in their yards and gardens.

The National Weather Service says the flock of butterflies were both dense enough and unusually high in the air that they appeared on the radar.

So much for the thought of an alien invasion or a horror movie-like attack of birds descending on Denver.