Mysterious Electric Blue Sea Creature Washes Ashore in the Thousands [VIDEO]

Thousands of mysterious, electric blue sea creatures have washed ashore at several beaches along the Northern California coast as of late, and scientists speculate as to what has brought them to the surface.

Now identified as velella velella, these jellyfish-like invertebrates have invaded the coasts of Monterey, Humboldt County, San Francisco and elsewhere, and sightings as come from as far as Oregon.

Strikingly blue and about the size of a hand, the US Coastguard mistook the species for an oil spill in 2002 when millions of them clumped up along the Bay Area coastline, SFGate reported.

Velellas live offshore, on the surface of the water, using their long tentacles to reach down and catch food, which includes fish eggs, plankton and other tiny sea organisms. The mysterious sea creatures have washed ashore before, but beachings are usually difficult to predict, according to Jim Watanabe, a lecturer at Stanford University's Hopkins Marine Station in Pacific Grove.

"It's been eight years, plus or minus, [since] we've seen them," Nancy Black, a marine biologist and owner of Monterey Bay Whale Watch, told San Jose Mercury News. "Why they've come now, it's hard to say."

"They go where the wind goes," Watanabe told SFGate. This year's wind patterns, he adds, are likely the reason for the velellas washing up on shore.

It is also for this reason that these creatures are also referred to as "by-the-wind sailors."

Kate Cummings, a naturalist and co-owner of Blue Ocean Whale Watch in Moss Landing, suspects warmer ocean temperatures - water temperatures in Monterey Bay are nearing 65 degrees Fahrenheit (18 degrees Celsius) - are behind their return.

"By Sunday afternoon we were seeing hundreds of them grouped together," she said.

Though it's unusual for thousands of velellas to come ashore this time of year - they typically bloom and float towards coastlines in the spring - experts say it's nothing to fret over.

Beachgoers near San Francisco took to social media to share photos of the beached blue colonies. And while they are toxic to their prey and are associated with their dangerous cousins, Portuguese man o' wars, velellas pose no danger to humans. Still, it's recommended that you don't touch them.

Velellas are meant to float on the water's surface, so when they are beached, they dry up.

If you pick these guys up and put them in the water and look at the under side, (you'll see) these tiny little tubular polyps and tentacles and other sort of things, which is the living part of the animal," Watanabe added. "If it isn't face-down in the water then they can't make their living - they'll dry out on beach quickly."