It's not every day that it rains cats and dogs. It's even rarer to be raining earthworms, which just occurred in Norway.

Karstein Erstad was skiing in the mountains Sunday outside of the coastal city of Bergen in western Norway when he chanced upon thousands of earthworms on top of the snow. The biology teacher though they were dead but when he picked some up, they appeared to be alive. At first he thought that the earthworms might've crawled from the ground underneath through the snow. After some thought, he rejected his own idea because snow can be as thick as three feet in some parts so the earthworms would have frozen before they got out into the open.

After Erstad's discovery made it to the national news, reports came in saying earthworms were also reported raining down in Suldal and Lindas, near Bergen, and as far away as on the other side of the country on the Swedish border in the town of Femunden.

"It's very peculiar. I don't know why so many people have discovered it," said Erstad, noting that he wasn't sure if the phenomena was associated with some kind of weather event.

At the very least, it has been established that this is not the first time that it has rained earthworms. The phenomenon is still very rare, though, making it difficult to say exactly just how many times it has occurred, although it has been reported to have happened in the 1920s in Sweden and in 2011 in a Scottish Academy secondary school.

So what could've caused earthworms to rain on Norway?

One theory suggests that the earthworms may have been taken for a ride by a violent pocket of air, taking them up and dropping them down miles from where they were picked up. Another theory points to water spouts, tornado-like weather systems traveling from the sea and onto land. Anything a water spout picks up is then carried miles away, falling to the ground when the weather event dissipates.

While there's still no word on what could've caused the rain of earthworms, those with religious inclinations have associated the event as something biblical. Some of the other instances when animals rained on Earth include live minnows in Wales in 1859, live frogs in Gibraltar in 1921, maggots in Mexico in 1967, smelt and flounder in London in 1984 and some more fish in Hertfordshire in 1996.

Photo: Arthur Chapman | Flickr