Hundreds of dead large squid have been washing up on beaches in Orange County, California, puzzling scientists.
Jumbo squid are thought to be plentiful in deep waters
The creatures - which can reach 1.8m long (6 feet) and weigh up to 7.7kg (17lb) - normally inhabit deep waters and only come to the surface at night.
"These things are invading, and we don't know what's going on," an oceanography professor said.
A similar invasion of jumbo squid was reported further down the coast near San Diego in 2002.
Between 500 and 1,500 squid - thought to be Humboldt squid - are said to have strewn beaches in Orange County, including Newport Beach and Laguna Beach.
"They look like a miniature sea monster, something you'd see out of a Jules Verne novel," a lifeguard at Newport Beach, Eric Bauer, told local newspaper the San Diego Union Tribune.
Although aggressive predators underwater, with powerful tentacles and a sharp beak, scientists say the squid pose little threat to humans.
But because the dead squid began washing up on Tuesday, authorities have warned they could harbour bacteria - and are still capable of squirting out ink.
The squid have been described as looking "like aliens"
A range of possible reasons for the sudden beaching of the squid have been suggested - from recent heavy rains, to plentiful shoals of fish close to the shore, to strong tides.
"These things are invading, and we don't know what's going on," John McGowan, professor emeritus at Scripps Institution of Oceanography in La Jolla, told the San Diego Union Tribune.
"It may be they're following a warm California current. Oceanographers don't have a clue why a large population of squid like this is moving north or why they strand themselves."