Tiny Killers of the Sea

When people think of dangerous animals, they tend to think big. Megalodon-size sharks, giant squid capable of sinking ships — that sort of thing. But the deadliest creatures in the sea, pound for pound, are so small, you probably wouldn’t think twice. The secret weapon? Venom.

For instance, a small, often painless, bite from the beautiful blue-ringed octopus can contain tetrodotoxin, which it uses to hunt. A 25-gram octopus carries enough of this powerful toxin to fatally paralyze 10 adult humans. Cone snails use their barbed tooth like a venom-laced harpoon to inject a cocktail that can contain hundreds of different toxins to instantly paralyze fast-moving fish.

Research suggests that the snails can combine these components on the fly, adapting their venom to the situation at hand. Some of these substances are being researched as potential pharmaceutical products — one compound was found to have pain-relieving properties 10,000 times more potent than morphine.

Beaked sea snakes can deliver enough venom in a single bite to kill five people, but fortunately, of the few bites that do occur, most are “dry bites,” in which no venom is injected. These three venomous creatures have the power to kill humans, but unless you threaten them, they’d just as soon live and let live.

Animals that rely on venom for protection generally aren’t able to “attack” others. Take the flower urchin, for instance — this 6-inch echinoderm’s lovely petallike appendages each end in three venom-wielding claws. It won’t be chasing anyone down, but come too close and you’ll wish you hadn’t.

The stonefish is another infamous example of extreme defensive measures. In fact, the stonefish cannot eject its own venom; rather, the pressure from a predator’s jaws clamping down or the weight of an unfortunate foot are what drive the fish’s spines into the victim and contract the attached venom sacs, delivering the nasty stuff deep into the wound.

Fortunately, if you keep your hands to yourself and watch where you put your fins, you should be able to prevent an uncomfortable close encounter.

The Australian box jellyfish is widely considered to be the most venomous marine animal, and one of the most dangerous ones on the planet. Just 6 feet worth of tentacle can carry enough venom to kill a human in two minutes.

Their 60 boot-lace-like tentacles each hold about 5,000 stinging cells called nematocysts. Simply brushing against the tentacle of a box jelly, aka sea wasp, is enough to trigger the nematocysts. Fortunately, wearing a wetsuit or other exposure protection can greatly reduce your chances of being stung.