Their scientific name is Velella velella, but they're popularly known as by-the-wind-sailors or purple sailor jellyfish, and they're washing ashore by the thousands along the Oregon, California and Washington coasts.
"They are super abundant offshore, but they only wash up on beaches when the wind blows just right,'' said G. Curtis Roegner, a research scientist at the Point Adams Research Station of the U.S. National Marine Fisheries Service in Hammond.
On a research vessel in late June off the Oregon coast, Roegner and his colleagues observed and took samples of the large mass of the floating organisms.
A combination of critters make up the jelllyfish colony: some feed, some sting and the one on top has a thin ridge, or sail, that propels them across the ocean surface.
If the wind blows at right angles to their sails, they're pushed ashore, Roegner said.
"It's definitely a wind event,'' he said.
According to Oregon State University researchers, the sails are set diagonally along the axis of the jellyfish in a northwest to southeast direction in the northern hemisphere. In the southern hemisphere, the sails are reversed.
Most of the time, the winds keep the animals offshore, but when strong westerlies blow, the jellyfish spin and start to follow the wind, driving them onto the beach.
Although they're harmless to humans, they do sting their prey, OSU researchers say. If you touch one it won't sting, but like handling hot peppers, don't rub your eyes or put fingers in your mouth.
--Stuart Tomlinson