Riding the wind and ocean currents, hordes of blue, alien-like creatures have descended upon South Florida's shoreline, entangling beachgoers in poisonous tentacles and delivering painful stings by the hundreds.
Each invader, in fact, isn't even an "it" but rather a "they," a colony of independent life forms that combined to create a single entity: the Portuguese man-of-war. The seafaring wanderer with the neon-blue gas bag and tentacles of up to 30 feet seems more suited to a sci-fi horror flick than a sunny, tourist-laden beach.
The man-of-war is a seasonal visitor here every winter and early spring, driven onshore by southeasterly winds and the Gulfstream's current. But this year's swarm arrived in far greater numbers than usual.
"It was unbelievable," said Crystal Haire, a lifeguard with Fort Lauderdale Ocean Rescue. "I've never seen that many at once. The shoreline was blue."
But the man-of-war's day in the South Florida sun may be near an end. Offshore winds from an approaching cold front should force the swarm back to the depths.
Over the weekend, hundreds of beachgoers were stung. Fort Lauderdale lifeguards treated 122 on Sunday, and 25 on Monday. Delray Beach lifeguards saw to 197 stings on Sunday, and 30 to 50 on Monday.
"There were just so many coming in all at once, it was rare the numbers we had," said James Scala, superintendent of Delray Beach Ocean Rescue. The man-of-war numbers fell slightly Monday, and since there were fewer beachgoers, there were fewer stings.
The man-of-war, or Physalia physalis, is bobbing testimony to nature's imagination. It is not a jellyfish — those floating mouths are way more normal than the man-of-war, also known as the bluebottle for the purplish bladder that keeps it on the surface.
"The Portuguese man-of-war is an oddball," said Charles Messing, professor of marine biology at Nova Southeastern University. "It's a bizarre thing."
Take that bladder: it's full of gas, mostly nitrogen, but 13 percent carbon monoxide. The crest atop the bladder catches the wind, propelling the creature across the sea. The crest also may have accounted for its name, since it resembles an old warship, or man-of-war, at full sail.
Its blue color could result from the sun. "It may be sort of a sunscreen kind of pigment to deal with the intense sunlight at the sea's surface," said Messing.
And the bladder can deflate, for when Physalia decides to submerge. Though it can't really decide because it doesn't have a brain, only a network of nerves.
The creature is composed of four separate organisms, or polyps. The bladder is one. The poisonous tentacles, which average about 30 feet, make up another. The third polyp is the animal's digestive system, and a fourth is in charge of reproduction.
Reproduction is simple, since the man-of-war is a hermaphrodite, with both male and female sexual characteristics. It just deposits into the water sperm and eggs, which fertilize and grow into larvae.
To eat, the man-of-war trails tentacles in the sea, ensnaring small fish and crustaceans. The venom-filled tendrils paralyze prey and pull it into multiple mouths. Because the man-of-war doesn't have a "backside," shall we say, waste material must go out the same way food comes in.
Some fish, immune to the poison, live among and feed upon Physalia's tentacles, which regenerate. Loggerhead turtles, however, are fond of eating the entire man-of-war.
The man-of-war likes warm ocean water, and sometimes travels in groups of 1,000 or more. Tendrils can detach and sting swimmers, and their poison remains active for more than a week after being severed from the main body, or even after the creature is dead.
To humans, the sting is painful and can last more than an hour. It can cause welts or a severe allergic reaction in someone with an impaired immune system.
But these invaders may soon be driven back to the sea from whence they came. Forecasters with the National Weather Service predicted a cold front overnight Monday will bring northwesterly winds.
"That's a good thing for all of our beachgoers," said Scala, of Delray ocean rescue. "The man-of-war are going to get blown away."