The Wasp That Brainwashed the Caterpillar

by Matt Simon

  The aye-aye is as good a demonstration as any of the awesome power of natural selection and the interrelatedness of all living things. Going even further back than the ancestor we share with the aye-aye, hundreds of millions of years ago fish dragged themselves onto shore with almost handlike fins, structures that may have evolved to help them escape from predators in the water. Those fins were a blueprint. The fish evolved into a wide variety of tetrapods (meaning “four-footed”)—all land-bound vertebrates like the amphibians and reptiles and mammals and birds—but the blueprint remained. The sociable weaver’s fin is a wing, the antechinus’s a paw, ours a hand, and the aye-aye’s a hand superspecialized for capturing grubs, because we’re all descended from a common fish ancestor.

  Owen was a piece of work but he was right, however accidentally right he may have been: There’s a blueprint, and a beautiful one at that, which the automatic forces of natural selection have modified time and time again as a solution to certain problems. You and I, Ebenezer Scrooge and the aye-aye, the Surinam toad and the pink fairy armadillo, we’re all that same fishy design customized for different purposes, for it’s the limb that binds us.

  Mantis Shrimp

  PROBLEM: All kinds of seafloor critters have robust armor, thus requiring the right utensils to eat them.

  SOLUTION: The mantis shrimp deploys hammer-hands that strike its prey so fast they momentarily heat the surrounding water to the temperature of the sun’s surface, splitting clams and crabs to pieces.

  Biologist Lindsey Dougherty specializes in the disco clam because, as far as clams go, it’s pretty amazing, with its gaudy, rapidly flashing bands that run along its mantle. At first glance you might think that the creature is bioluminescent like the anglerfish’s lure. But instead of producing light, this is special tissue that’s so reflective that it fires bright light at your eyeballs. Dougherty had a hunch that the show was meant to scare away predators, so she got a creature so fearsome, so ornery, so powerful, that you’d expect the clam to flicker like it never flickered before.

  She got herself a shrimp.

  Okay, maybe that’s a bit misleading. Even though it kind of looks like one, the mantis shrimp isn’t a shrimp, but another crustacean known as a stomatopod. But all that other stuff is true—these things are mean, immensely powerful, and not to be messed with. There’s a reason they’re called thumb splitters.

  As Dougherty’s camera rolled, the stomatopod approached the disco clam, grabbing it and sizing it up. But the master predator suddenly recoiled. And approached again. And recoiled again and approached again and recoiled and then for some reason went catatonic, before snapping out of it and proceeding to hump the clam. I’d like to think that the stomatopod was so frustrated by the fact that it had come across something it couldn’t murder that it could no longer cope with reality, but in actuality it probably had more to do with the sulfur in the disco clam’s flowing tentacles having some sort of effect. Still, stomatopods are not used to giving up. If something is a reasonable size to attack, chances are a stomatopod is equipped to destroy it. This business with the disco clam, it was a fluke.

  There are two types of stomatopods, the spearers and the clubbers, distinguishable by the weaponry that sits below their face. The mantis shrimp get its name from the first group: It has two spiked arms that look much like those of the famous insect, only flipped upside down (it snags fish from below, grabbing them like you’d carry a bundle of sticks on your forearms). This kind tends to dig burrows in the sand, lashing out at passing fish so quickly that the strike is almost invisible to our eyes, before disappearing back into its lair, leaving only a shimmering cloud of scales for evidence. It’s so fast, in fact, that the world expert in the mantis shrimp’s strike, Sheila Patek, couldn’t at first film it because her university’s cameras weren’t able to capture enough frames per second. Only when a BBC crew showed up did Patek get her footage: She convinced them to rent a brand-new camera model powerful enough to pull it off—in exchange for giving them a story, of course.

  IT’S ONLY OKAY TO ATTACK KITTENS THAT ARE EVIL

  Crustaceans like the stomatopods get typecast as marine creatures, but there are plenty of terrestrial varieties. Your average pill bug—or roly-poly, or whatever you like to call it—is in fact a crustacean. And then there’s the mightiest land crustacean of all: the coconut crab. It’s a kind of hermit crab, only it forgoes the shell and grows to three feet across and ten pounds. The crab’s claws are so powerful it can tear through coconuts, as its name suggests. On the islands in the Pacific the coconut crab calls home, it’s been known to attack . . . kittens. I’m sorry you had to read that, but who knows, maybe those cats were evil or something. It’s good to think positive, after all.

  But the strikes start bordering on the far-fetched with the clubbers. At work here is a surprisingly simple mechanism. Up at the top of the arm is a kind of membranous divot, curved like a saddle, that acts as a spring. The stomatopod contracts a big muscle in that arm, pulling back the club and compressing the spring until an internal latch snaps into place. That latch is holding back a tremendous amount of energy in the muscle, and when it flies open, the spring rockets the club forward at up to fifty miles per hour, which is especially impressive considering this is happening in water. The resulting force is devastating. Subjected to such treatment, clams shatter, while more fragile creatures like crabs explode into a shower of limbs. Indeed, a clubber stomatopod will target a crab’s claws first, blowing them off to counter the prey’s futile attempts to defend itself.

  Here, too, Patek realized that the stomatopod confounds human technology. When she went to measure the forces the clubber could produce, she found that the instrument she’d bought for the creature to smash was inadequate. It was rated for forces up to one hundred pounds, when it turns out the stomatopod can punch at well over two hundred pounds. When she finally got her readings with a different instrument, Patek noticed something strange. There was the initial force, but also a second impact that hit a fraction of a second later: cavitation bubbles. Like the pistol shrimp, the clubbing stomatopod is striking so quickly that it creates these supremely destructive bubbles, which spread over the surface of the prey and explode not just with a shock wave and temperatures almost equal to those on the surface of the sun—nearly 10,000 degrees Fahrenheit—but a flash of light. The strike is a one-two punch, an initial impact with a trailing explosion.

  You’d expect all the smashing to take a toll on the weapons themselves, and it certainly does. Patek has seen stomatopods wear their clubs down to the muscle (again, these things are plain ornery, not to mention hungry). But by virtue of being an arthropod—that is, an invertebrate that among a few other defining characteristics has an exoskeleton—it can shed that armor and grow it again, complete with shiny new clubs. Sure, there’s a bit of a perilous period there as it waits for its shell to harden up, but that’s nothing a little bluffing can’t fix: When threatened during this time the stomatopod won’t smash, but instead waves its arms around and hopes that’s enough to deter predators.

  THE ANTS THAT WOULD BE POPCORN

  Sheila Patek has become the go-to scientist if you’re looking for information about the fastest, most powerful strikes in the animal kingdom. Besides the mantis shrimp, her other interests include the trap-jaw ants. Like the clubber stomatopods, they use a latch mechanism to cock their mandibles and store up tremendous energy. Special hairs on those mandibles trigger the strike when they brush up against prey, crushing or launching the stunned victim through the air. And when threatened, trap-jaw ants even turn their weapons on themselves. By pointing their mandibles at the ground and firing, the ants fling themselves away from danger, tumbling end over end. Disturb one of their nests and they’ll do it en masse, popping off like angry popcorn.

  Really, it’d be hard to overstate what an amazing tool the exoskeleton is for the stomatopod and the other arthropods that swim or fly or walk the Earth. It wi
ns those mantis shrimp meals and keeps them from blowing their own arms off, but it also provides protection from predators and the elements. And as we’ll see in a bit, the exoskeleton has played no small part in helping the beetles, of all things, conquer the Earth. The shell can take on all manner of colors for advertising sexiness to mates or poisonousness to hungry enemies. It can form into bizarre structures, while we mammals are pretty much stuck with these fleshy vessels.

  That’s not to say we’re chopped liver. Those exoskeletons keep arthropods from growing too big, since they start getting prohibitively heavy at a certain point, whereas vertebrates can grow enormous with their endoskeletons as support. It’s just that evolution has gifted invertebrates and vertebrates with different strategies. We got our great big brains and the stomatopods got their weaponry. And that, quite frankly, is fine by me. Being strong enough to punch through a clam is a lot of responsibility, after all.

  Bone-Eating Worm

  PROBLEM: The deepest of seafloors are desolate, and food is in short supply.

  SOLUTION: A certain worm has hit upon the idea of boring into the skeletons of creatures that have sunk to the bottom, dissolving and digesting bone with the help of friendly bacteria.

  Creatures are dependent on sunlight in surprisingly complex ways. The organisms with the first dibs on sunshine are the plants, which use it in photosynthesis. The sun’s energy is then passed up the food chain, to the bugs that eat these plants, to the birds that eat the bugs, to the mammals that eat the birds.

  The same goes in the oceans. Plantlike phytoplankton float around absorbing the sun’s energy. Zooplankton eat the phytoplankton, and fish eat the zooplankton, on up the line. Every critter in that food chain, though, meets its end and sinks down into the abyss, a biomass that’s known quite tranquilly as marine snow—even though it’s made of dead things. Opportunists in the water column pick at this marine snow as it falls, and accordingly very few nutrients even reach the seafloor. So few nutrients, in fact, that a whale that dies and sinks more or less intact to the bottom (there may be opportunists, but not enough to strip a whale clean before it hits the floor) will provide as much food to the critters of the seafloor as would thousands of years of marine snow. The so-called whale fall is what the scavengers of the seafloor are desperate for. They’ll pick the giant’s bones clean and won’t stop at that, for there are creatures that devour the bones themselves.

  Worms of the genus Osedax are quite beautiful, being one or two inches long with a white tube of a body, at the end of which erupt red or pink or orange frills, known as palps, which gather oxygen. But it’s what you can’t see that’s so amazing about the bone-eating worms. Down inside the whale’s bones are worms’ guts. Well, gutlike organs. The worms don’t have mouths and they don’t have intestines. Instead, they send “roots” down into the skeleton, forming a structure that varies between a simple bulb and thinner, wandering shoots, depending on the worm. These roots release massive amounts of acid, while inside are symbiotic bacteria, which take the fats and proteins absorbed through the worm’s tissue and convert them into energy. All the worms have to do is sit there—oftentimes in vast sheets covering the skeleton, swaying gently with the current like tiny trees sucking up groundwater—as the bacteria go to work. In exchange, the bacteria get themselves nice little homes.

  OSEDAX: MUCKING UP THE FOSSIL RECORD FOR 100 MILLION YEARS

  Getting fossilized is a pretty tall order. The conditions have to be just right—dying in sediment helps—but even then you have to hope that scavengers don’t cart you away in pieces first. Soft-bodied creatures like worms are especially resistant to fossilization, but that doesn’t mean they don’t leave behind evidence of their existence. For instance, scientists have found the fossilized bones of sea turtles and plesiosaurs (those fearsome, long-necked marine reptiles) bored through with holes, showing that squishy old Osedax, having resisted fossilization itself, has been mucking up the fossil record for at least 100 million years. Excuse me. The bone-eating worms, in the words of the scientists, “may have had a significant negative effect on the preservation of marine vertebrates in the fossil record.” Yes, that sounds much more scientific.

  Surprisingly enough, though, eating bones isn’t a big deal. Hyenas do it with their powerful jaws, biting off bits of ribs like you or I would eat sticks of celery. It’s how the bone-eating worm does it that makes it so unique in the animal kingdom—no other animal feeds in this way—not to mention how dependent it is on the strategy. Bones for a hyena are dessert after a main course of flesh, but for the bone-eating worm, skeletons are all it has. On the menu is liquefied bone, always and forever. And the worm is lucky it even has that. It isn’t every day that a whale dies and sinks to the bottom of the sea, and it’s certainly unlikely that two will fall right next to each other. So the bone-eating worm stakes its claim, permanently anchoring itself into a whale bone and chowing down.

  Such immobility would seem to present a problem for mating. Even more problematic, scientists at first were finding only females on the whale bones. So where were the males? It wasn’t until researchers opened the worms up that they found microscopic males inside the females, up to one hundred of them, about one hundred thousand times smaller than their mates. Really, the males are simply sacs of sperm and yolk. Unable to feed themselves, they live off the yolk afforded to them at birth, producing sperm as their food supply dwindles, until their seed is gone, their sustenance is gone, and their body cavity is empty.

  But how do the males find the females? Well, scientists reckon that bone-eating worm larvae float around on currents and will develop into males only if they land on a female. Those that land on bones anchor themselves and become females, developing into that lovely worm and waiting for a lucky soon-to-be male to arrive. When that happens, their gametes will mix and the female will release her young into the current, thus spreading the worms around the seafloor. It all may sound overly complicated, but it makes good evolutionary sense. Males that don’t feed don’t need to worry about competing with females for the scant food on the seafloor. And by permanently attaching himself to a female, the male all but guarantees he can pass his genes along. The whole thing is remarkably similar to the goings-on of the sex-changing tongue-eating isopod, not to mention the anglerfish: Males never eat, and when they find a lady, they’ll be damned if they’re going to let her slip away.

  DYING TO GET LAID

  Sexual internment sounds like a raw deal, but it could be much worse for the male Osedax. Some fellas in the animal kingdom pay for sex with their lives—and by that I mean the females eat them. One theory for why this happens posits that by eating the male, the female gains valuable nutrition to put toward developing her young. Thus, the male has a better chance of passing his genes along even though he’s dead. Indeed, one study of praying mantises showed this, with females in crummy shape being more likely to snack on their mates than their healthier counterparts. The cannibals in turn increased the weight of their egg cases . . . and significantly reduced the odds of the male ever calling back.

  Strangely, though, there’s one particularly tiny species of bone-eating worm, Osedax priapus, that’s evolved away from this mating system. Its males are much closer to the size of the females— they’re only about three times smaller, as opposed to one hundred thousand times smaller. Males don’t attach to females, but instead stretch their bodies to hand sperm off to their neighbors. So why deviate? The reason could come down to Osedax priapus’s small size. Males in other species of bone-eating worms may have evolved into dwarfism because of competition over food: These things totally swarm whale skeletons, so if the male doesn’t need to feed, all the better. Osedax priapus is so tiny, competition to feed on a given bone might never have been a problem. The clingy dwarf Osedax males may have a guaranteed mate for life, but the large males of this particular species can gorge themselves on bone, gaining more energy to produce sperm, plus they can mate with multiple
females instead of committing to one.

  So in the end, it comes down to food provided by the sun. Zooplankton eat the solar-powered phytoplankton, and the whale at the top of the food chain eats the zooplankton, before perishing and falling and serving itself up to the creatures at the very bottom. An Osedax worm finds a bone, and an Osedax larva finds an Osedax lady, and the rest is a story for their grandkids.

  Wait, that’s not a good story to tell the grandkids. Disregard that.

  Tiger Beetle

  PROBLEM: Your prey are quick footed.

  SOLUTION: The tiger beetle one-ups them by running so fast it blinds itself and has to stop every once in a while to get its bearings. Not that it matters. This is a supreme sprinter with a stomach to fill.

  In October 1858, four years into his travels hopping between the many islands of Southeast Asia, Alfred Russel Wallace found himself in a clearing in a forest, where he apparently interrupted some kind of grand Snow White–esque meeting of animals. Specifically, beetles: There were weevils and longicorns and gorgeous golden varieties—so many beetles, he recalled, “that they rose up in swarms as I walked along, filling the air with a loud buzzing hum.” As any self-respecting naturalist would do, he returned to the clearing for the next three days, collecting some one hundred different species. All in a single jungle clearing.