Mother Nature Is Trying to Kill You (22 page)

The Australian box jellyfish is easily the most deadly jellyfish to humans, but the vast majority of jellyfish species aren’t dangerous
to humans at all. Sometimes a jelly’s harpoons are simply too small to make it through our skin. Other times, the chemical structure of the venom just doesn’t have a lethal effect on the human body. For instance, there’s a huge jelly you might have heard of called a Portuguese man-of-war. This jelly can have up to thirty harpoon-loaded tentacles, each about a foot long, that can quickly kill a fish. But despite urban myths to the contrary, the Portuguese man-of-war is extremely unlikely to kill a human (even though humans will feel a world of pain if they are stung).
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There’s another animal out there that is even less susceptible to the stings of a Portuguese man-of-war than humans are, even though it’s just a tiny thing, only about an inch long. In fact, what it can do with the jelly’s stingers might be one of the most unbelievable tricks in all of biology. Back in the chapter on gluttony we talked about the emerald sea slug, which gets its energy from the sun by eating algae and moving the solar-powered molecular machinery to the surface of its own skin. Taking a page from the same book, there’s another kind of sea slug, called the blue dragon, that eats the stinging tentacles of a Portuguese man-of-war without setting off the harpoons. Then, like its solar-powered cousin, the blue dragon moves those harpoons to its own skin for protection.
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The Latin name for this stinging sea slug is
Glaucus,
after the Greek sea god who was born a mortal but became immortal when he ate a magical herb. What a perfect name for such an unusual creature. It avoids getting stung itself by covering its skin with
a mucus that chemically inhibits the man-of-war harpoons from firing. The blue dragon also has specialized skin cells that can absorb any harpoons that do fire, almost like sandbags, preventing the venom from leaking into its body. Since the blue dragon eats the harpoons, it has similar linings in its mouth and all along its digestive tract as well. Once the harpoons are ingested, they’re taken up by specialized mover cells and then placed out at the skin of the animal. There they are kept alive by secretions from the blue dragon’s body, ready to fire if the blue dragon needs protection.
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While that particular sea slug has to steal venom from jellies, it has some close relatives called cone snails that can make venom on their own. You might think of snails as slow, harmless creatures, but those are not words you can use to describe cone snails. Cone snails live in tropical oceans, where they feed on fish, crustaceans, and other prey you would think are too fast for a snail to catch. But they absolutely can catch those prey, and they do so by firing a high-speed venom-tipped harpoon into the victim as it passes by. Cone snail venom is
extremely
deadly to humans, possibly the deadliest venom out there. In fact, a cone snail can kill a person in less than five minutes. Some people call them cigarette snails, because once you’ve been stung, you only have enough time for a last cigarette.
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Cone snail shells are, well, cone-shaped (hence the name), with a long slit along the side, out of which the animal emerges. They tend to be brightly colored with intricate patterns, making them absolutely beautiful. Once you know what they look like,
they’re unmistakable, so I can only assume that most of the people who have been killed by cone snails picked them up for their beauty, with no idea what they were. Or perhaps some of those victims did know the dangers of cone snails but assumed that their wetsuit gloves would protect them from the harpoons. But unlike the millions of microscopic harpoons that jellyfish have, the much larger, single harpoon of the cone snail is a modified tooth and easily large enough to penetrate a wetsuit.

Interestingly, the venom of a cone snail is almost painless because it contains powerful proteins that block pain.
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That makes them attractive animals of study for pharmaceutical companies: perhaps cone snails will someday reveal nonaddictive alternatives to drugs like morphine. That said, finding the pain-blocking proteins in cone snail venom is a bit of a needle-in-a-haystack problem. Each species of cone snail produces more than a thousand different proteins as part of its venom, and those proteins vary among the five hundred or so species of cone snail. In fact, the proteins can even change over the lifetime of an individual snail.
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Cone snails rarely kill humans because most humans don’t spend very much time underwater in the tropics at night, and those who do usually know enough about cone snails to stay away from them. That’s why, despite their extraordinarily deadly venom, cone snails have only been blamed for the deaths of around thirty people.
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Instead, people are much more likely to be envenomed by creatures that live where humans do, back up on land—things like spiders.

There are more than 44,000 species of spiders in the world
and almost every one of them is venomous.
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Most don’t hurt humans though, either because they don’t bite in defense, because their fangs can’t pierce human skin, because they produce such a small amount of venom, or because their venom just doesn’t happen to react chemically with the human body. Of those spiders that do cause problems for people, most only cause short-term pain and swelling right at the site of the bite. For the most part, despite their abysmal popularity ratings, spiders aren’t really anything to worry about at all. That said, there are a few out there that can do considerable damage, and spiders from a few select groups have actually killed people. Overall, though, deaths from spider bites are vanishingly rare. Even the bites of spider species that
can
kill humans are almost always nonlethal.
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Spiders deliver venom through stingers on either side of the mouth, and most spider venoms are neurotoxins. In other words, they’re chemicals that affect neurons. Neurons are the cells in your brain that enable you to think, and they also run down your spinal cord and out into nerves branching throughout your body. Insects have neurons too, and it’s usually those insect neurons that spider venoms target, since most spiders eat insects. Whether or not those venoms, intended for an insect’s neurons, will have any effect on a human is mostly a matter of luck. Some spider toxins have no effect at all on humans. But others work
very
well.

A neuron is a long cell with branches at either end that interact with the branches of other neurons. A message travels along the length of a neuron until it reaches the end. To continue, the message must be passed on to another neuron. The first neuron passes on its message by releasing chemicals called neurotransmitters from the tips of its branches. Those neurotransmitters float across the microscopic space separating the branches of the first neuron from the branches of the next, and once they’ve made it across (a process that takes only milliseconds because the distance is so short), the receiving neuron fires, sending that electrical wave down the length of its own body, on toward the next neuron in line. This whole process is unimaginably fast and can obviously only happen if the neurons are working properly.

Many spider venoms affect the neurons of their prey by throwing off the ability of neurons to control their electrical charges. That means that when the neuron receives a message to fire from the neuron before it, it short-circuits. Different venoms accomplish this in different ways. Some cause the neurons to leak potassium, others sodium, and still others calcium. In their own way, each of these can make a cell go haywire. What’s worse, the venom of any particular spider typically contains many different neurotoxins, each of which messes up neurons in slightly different ways.

In addition, spider venoms often also contain other chemicals that cause swelling and pain.
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Unlike the neurotoxins that are intended for insects, those other chemicals make the venom especially effective for protection against larger animals that could hurt the spider—animals like us.

The most deadly spider in the world to humans is a half-inch
to two-inch black beast with massive fangs called the Sydney funnel-web spider. There are other funnel-web spiders in other parts of the world, but none of those are very dangerous at all. Sydney funnel-web spiders, though, are very different. They’re aggressive, they live right around a city with a population of 4.5 million people (Sydney, Australia, in case you hadn’t guessed), and their venom contains a particularly nasty neurotoxin that messes with the neuron’s ability to control sodium movement in and out of the cell. For whatever reason, the venom of that particular spider is especially hard on humans. In fact, the venom of the Sydney funnel-web spider doesn’t really do anything to cats, dogs, rats, or other nonprimate mammals. It’s just really effective on primates, even though primates aren’t native to Australia.
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An antivenin now exists for the venom of the Sydney funnel-web spider.
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It’s created by taking the venom out of several Sydney funnel-web spiders, then injecting them into a rabbit, at first in small doses, and then in larger and larger ones. Over time, the rabbit builds antibodies to the venom, until eventually its blood is full of antibodies specifically made to attack the neurotoxins in that spider’s venom. Then the rabbit’s blood serum (blood without the red blood cells, basically) is drawn and stored in vials. Later, when someone gets bitten by a Sydney funnel-web spider, the person is injected with antibody-laden rabbit serum. That gives the human’s immune system some help breaking down the neurotoxins, rendering the venom of the spider nonfatal. It’s a great trick, and since the antivenin was created, in 1980, there hasn’t been a single fatality from the Sydney funnel-web spider (knock on wood).
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A lot of people find spiders creepy, but if there’s a creepy crawly out there that makes people even more nervous, it has to be the scorpion. Scorpions are eight-legged arachnids, like spiders (as opposed to six-legged insects). Like spiders, scorpions also have venom, but instead of delivering it through the mouthparts, scorpions, as everyone knows, sting you with their fabulous tails.
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Scorpions have existed, mostly unchanged, for more than 400 million years, since well before the dinosaurs and before other animals had yet come on land, including insects and our own ancestors for that matter. The biggest scorpions alive today are just over eight inches long, but millions of years ago there were three-foot-long scorpions walking around, which have since been given outstanding names, like
Gigantoscorpio
and
Brontoscorpio
. (With names like those, it’s hard to believe they haven’t yet been featured in some dreadful made-for-TV horror movie.) In all likelihood those animals lived in the water, where buoyancy would have helped them support their enormous bodies. But still, it’s sobering to imagine coming across one.
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There are more than 1,500 scorpion species out there, and of those, 25 or so have a sting that can kill a human. Despite that small number, roughly five thousand people around the world die each year due to scorpion stings, making bees and snakes the only venomous animals that kill more humans.
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The first time I ever came across a scorpion myself was in
Belize, on one of those field excursions for my master’s degree. I was lying in a hammock under a thatched roof when someone pointed out a scorpion crawling on the wall above my head. I leapt up, grabbed a pair of long sticks, and then used them like chopsticks to move the scorpion delicately out into the sunshine so I could take photos of it. As I shot the pictures, it first went into a great defensive pose, holding its tail and claws up perfectly for the photos, but then it suddenly went limp and died. I had no idea what killed the scorpion, but I carried it over (with the sticks—I was still too scared to touch it) to show it to the other biologists there. One of them picked it up to show me some of the anatomy on its belly, and then as we ate lunch the scorpion got passed around the table for everyone to see. Later, I was carrying the scorpion in my hand back to my cabin, trying to decide whether I should attempt to bring this thing home through customs, when it suddenly leapt back to life and ran up my arm. I screamed—
screamed
—and swatted the scorpion into the air. It landed on the ground, then walked nonchalantly away like nothing had happened. I wasn’t stung, but now that I know a scorpion can play dead for three hours at a time, I know not to trust them ever again.

Like spider venoms, many scorpion venoms are neurotoxins. So even if you don’t die, a sting from the wrong scorpion can cause paralysis, convulsions, and heart palpitations. Like most venomous creatures, scorpions use their venom primarily to subdue prey while hunting but also make use of it to defend themselves against predators. Most of the time that works really well, but unfortunately for the scorpions, venom doesn’t work against all the predators all the time. For proof of that, look no further than the pallid bat, which specializes in eating scorpions.

The pallid bat is a gorgeous yellowish-white bat from the deserts of western North America. It weighs about as much as a sparrow, though it seems bigger when you see it in flight. The first things you notice about a pallid bat are its big, beautiful ears. When you look more closely, though, you’ll see that it also has intricate, scrolling nostrils that give it unique appearance, even among bats. When it hunts, the pallid bat either sits on a perch or flies silently, listening carefully for the footsteps of large insects or arachnids. When it hears those sounds, it hovers over the spot to get a closer “look” with its echolocation, then flies down to kill its prey.
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If it’s a scorpion, the first thing the bat does is rip off the stinger. Sometimes, though, the bat’s just not fast enough and gets stung anyway. There’s good evidence that scorpion stings do hurt the bats: pallid bats fed nothing but scorpions for several days will go after them with gusto on day one but seem to lose their enthusiasm as the days wear on. Some researchers have even caught pallid bats that were missing an eye, presumably from a well-placed scorpion sting.
Scorpions are a tough food to eat, but pallid bats are hard-core.
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