The sky is an immense bowl of blue and the boiling-hot sun speckles the flat green waters gold as our boat edges out of Port Douglas, Australia, just north of the tropical resort town of Cairns. On board, tourists from around the world are heading for the Great Barrier Reef, the world’s largest natural structure—stretching for 1,400 miles along the continent’s northeastern coastline.
After a 90-minute journey, we arrive at Opal Reef, a chunk of the Great Barrier Reef five miles long and three miles wide, where frothy white waves break gently over shadowy outcrops of coral as big as houses. We throw on our snorkeling gear and slip quickly into the water, drifting over the shallow reef facedown, entranced by the multihued coral—some resembling giant brains, others massed like stag horns and mammoth fans—and the neon-colored small fish that dart in and out. Not one of the crew members has bothered to warn us that Opal Reef is where one of the planet’s deadliest creatures killed a visitor three years earlier.
Robert King, 44, from Columbus, Ohio, was snorkeling over the same underwater landscape when he felt a mild sting on his chest and came back onto the boat. Within 25 minutes his face flushed tomato-red as severe pain gripped his stomach, chest and back muscles. The skipper radioed for a medevac chopper, whose crew injected King with a massive dose of pethidine, an opiate-like painkiller, then winched him from the boat and rushed him to Cairns.
By the time he was wheeled into the emergency ward at CairnsBaseHospital, King’s speech was slurred. He was put on a ventilator, as doctors pumped him full of painkillers while racing to save his life. A local zoologist, Jamie Seymour, was called in to take a scraping of the sting site. While he worked, Seymour noticed that King’s blood pressure was spiking dramatically. King lost consciousness; then, Seymour says, “an artery or vein in his brain blew.” Blood flooded King’s brain tissues, and two days later he died.
After analyzing the shape and size of the stinging cells, which were about an inch long, Seymour blamed King’s death on a nearly transparent jellyfish the size of a thumbnail. Covered from the top of its head to the tip of its four tentacles with millions of microscopic spring-loaded harpoons filled with venom, it’s one of at least ten related species of small jellyfish whose sting can plunge victims into what doctors call the Irukandji syndrome. “The symptoms overwhelm you,” says Seymour, 40, who himself was stung by an irukandji on the lip, the only part of his body uncovered as he scuba-dived looking for specimens near an island off Cairns in late 2003. “On a pain scale of 1 to 10, it rated between 15 and 20,” he says, describing the vomiting, the cramps and the feeling of panic. “I was convinced I was going to die.” But he was lucky; not all species of irukandji administer fatal stings, and he recovered within a day.
So far, only King’s death—and perhaps that three months earlier of an Englishman, 58-year-old Richard Jordan, farther south on the Great Barrier Reef—can be attributed to irukandji venom, but Seymour cites research suggesting that because the symptoms may resemble strokes or decompression sickness, and can lead to drowning, countless more swimmers have probably fallen victim to Irukandji syndrome in offshore waters throughout the tropics. Stings from the irukandji species who live in waters closer to shore are rarely fatal but are still excruciatingly painful: for centuries before the tiny jellies were identified as the culprit, the local Aborigines at Cairns, the Irukandji tribe, knew that to swim in the shallows in the rainy season, from November to May, was to risk getting stung, although they didn’t know by what.
More ominously for residents of North America, doctors at the U.S. Army Special Forces Underwater Operations School at Key West, Florida, have treated military divers suffering from symptoms similar to the syndrome; U.S. Navy divers have seen Irukandji-like jellyfish in the waters off Cuba’s GuantánamoBay; swimmers have been badly stung in Hawaii; and the Gulf of Mexico and the adjoining southern U.S. Atlantic coastline have seen an increase in people being sickened by stings that almost certainly come from an irukandji or a related jellyfish.
Most jellyfish are passive; they drift up and down in the water column, or are pulled to and fro by the tides and winds. They float through the oceans devouring tiny fish and microscopic creatures that bumble into their tentacles, and are no threat to humans.
But those known as box jellyfish, for the shape of their bell, or body, are a breed apart. Also called cubozoans, they’re voracious hunters, able to chase prey by moving forward—as well as up and down—at speeds of up to two knots. They range in size from the various irukandji species to their big brother, the brutish Chironex fleckeri, which has a bell the size of a man’s head and up to 180 yards of tentacles, each lined with billions of cells bursting with deadly venom. Also known as a sea wasp or marine stinger, Chironex, which is far deadlier than irukandji, boasts powerful stingers, or nematocysts, strong enough to pierce the carapace of a crab and quick enough to shoot out at the fastest speed known in the natural world—up to 40,000 times the force of gravity. And unlike other jellyfish, a box jellyfish can see where it’s going and alter its course accordingly; like an eerie creature sprung from science fiction or a horror movie, it has four separate brains and 24 eyes, providing it a 360-degree view of its watery world.
“A Chironex fleckeri can kill a human in one minute flat,” says Seymour, widely considered the world’s foremost box jellyfish researcher. The most recent victim was a 7-year-old boy who died two years ago at a beach south of Cairns, becoming one of about a hundred people believed to have been killed over the past century by Chironex in Australia alone. (No one knows for sure how many swimmers have died from the stings of other box jellyfish outside Australia, but Seymour puts the number at “hundreds, possibly thousands.”) Survivors, those lucky enough to have been gripped by less than the four yards of Chironex tentacle that can kill an adult (or the two yards it can take to kill a child), suffer pain that one has described as “like having a bucket of fire poured on me” and are branded by macabre tentacle marks, scarlet tangled wheals that make the victims look as if they’d just been lashed at the mast. “Chironex is by far the world’s most venomous creature,” says Seymour. “It makes venomous snakes look like amateurs.”