The sedentary upside-down jellies form a figurative and literal garden in shallow reef waters as they extend their algae-filled, floral-looking tentacles and oral arms toward the sunlight. But when threatened, they release protective mucus loaded with nematocysts. Snorkelers whose swim fins ruffle these jellies may trigger the release of a nearly invisible sheet of mucus that drifts up, swaddles them and causes an itchy red rash as the stinging cells penetrate their skin.
Our young, golf-ball-sized lion’s mane jellies can’t do much harm. But by the time one reaches the size of the overhead model, with 50-foot tentacles that wind the length of the exhibit room, it is a stunning stinger. While sea turtles and some fishes can nibble away at these jellies with no ill effects, big lion’s manes can inflect a painful sting on people with their potent neurotoxic venom. Chemically short-circuiting the nervous system, the venom can paralyze breathing muscles, leading to suffocation. But this species is not aggressive (most jellies aren’t), and the colorful, sometimes colossal lion’s manes are visible enough to be avoided.
Bigger Isn’t Badder
The smallest jelly is among the deadliest. Australia’s little irukandji could nestle within a contact lens—although you wouldn’t want it there. A mere third of an inch in diameter, it’s one of the extremely venomous box jellies, another species of which tops the list of the world’s most toxic animals. Jellies houses a harmless model of the irukandji.
Its stinging cells are clumped in rings of small red dots—like a warning—around the bell as well as along the tentacles. Its venom is reportedly 100 times as potent as a cobra’s and 1,000 times as potent as a tarantula’s. And the formula is different from that of “true” jellies—the moons, nettles and other bell-shaped members of the class Scyphozoa. The squarish box jellies are stacked in class Cubozoa—still in that big stinging phylum Cnidaria—and they are more complex animals. They are predators capable of going after their prey, rather than waiting for it to bump into them as so many drifting jellies do, and they might need extra-strength venom to quickly stun the small, fast fishes they pursue.
A little venom goes a long way, however, and its effect on humans is called the irukandji syndrome: unbearable muscle pain in the arms, legs and back; kidney pain; a feeling that one’s skin is on fire; pounding headache; nausea; sweating; vomiting; skyrocketing blood pressure; furious heart rate (and even heart failure); and, not surprisingly, a feeling of impending doom. One Australian researcher with firsthand experience said that on a pain scale of 1 to 10, Irukandji syndrome rates a 40. This horrific suite of reactions is caused by catecholoamines in the venom, complex compounds that can act as chemical messengers that wreak havoc on how nerve impulses are transmitted. In the water, a person can go into shock and drown or die of heart failure before reaching shore. If he survives, he may have permanent scars where the tentacles touched his skin.
Irukandji syndrome typically hits within 30 minutes of receiving what is only an irritating sting. Hospitalization is the first course of action. Vinegar will deactivate any unfired stinging cells on the skin, but it can’t neutralize venom already in the bloodstream. Symptoms can last hours or weeks. Treatment includes antihistamines, antihypertensive drugs and intravenous morphine or other heavy-duty painkiller.
These tiny, transparent terrors are summer residents in Australia’s warmer coastal waters, putting them and swimmers on a collision course. Rising ocean temperatures, however, are expanding their range. Properly treated, a sting does not have to be fatal, but several deaths have been attributed to these little jellies. The larger box jellies kill 20 to 40 people a year just in the Philippines.
Prevention really is the best medicine with this group of jellies. Irukandji can pass through nets used along Australian beaches to create jelly-free zones. But their nematocysts can’t pass through pantyhose. Yes, pantyhose. Smart swimmers wear body stockings of pantyhose material—or wetsuits—as well as masks to avoid eye stings. Remember that fact about fitting in a contact lens.
The Sting That Keeps on Giving
Old nematocysts don’t die—at least not for a long time. Even when they’re not attached to a jelly, stinging cells remain viable—and venomous—for months. Severed tentacles, jellies chopped up in a boat propeller or washed ashore dead, and even stinging cells released or shed in the water will fire. So far, Shedd’s aquarists have not been zapped by any solitary stinging cells as they clean the Jellies exhibits.
Next time: A venomous surprise
Posted by Karen Furnweger, web editor