The Wasp That Brainwashed the Caterpillar

by Matt Simon

  It’s because all a water bear ever wanted was to survive a dry spell. As an added bonus, when they dry out, their husks can get caught up in the wind, which spreads them far and wide, so there aren’t many places you won’t find a water bear or two, from the deep sea on up to the tops of mountains. So I don’t know about you, but I sure am proud to share a planet with the water bear. Hell, I say we put them in rockets and fire them out into space to colonize other worlds so aliens can enjoy them as well. Or is that wildly irresponsible? That’s wildly irresponsible, isn’t it.

  Diving Bell Spider

  PROBLEM: Life on land is full of all kinds of nasty predators, as well as competition for food.

  SOLUTION: A certain spider leaves it all behind and goes aquatic, using its butt to collect a bubble of oxygen and start living in the water . . . permanently. This is the only spider that lives its entire life underwater.

  Life on land is no picnic. Well, it is a picnic if you happen to be near the top of the food chain. But if you’re toward the bottom, you are the picnic. Take the spiders, for instance. They’re master hunters in their own right, but all manner of other critters have them on the menu. So a spider looking to survive can hide and ambush its prey, like the trap-door spiders do, or mimic an unpalatable species, like a ladybug spider does, with its red-with-black-spots outfit (yes, ladybugs are toxic). Or you can take a page from the diving bell spider’s book and pack up and leave land altogether.

  I don’t want to tell spiders how to live their lives, but they really don’t belong in water. There’s the whole problem of, you know, breathing and stuff. But for that the diving bell spider has an incredible solution. Its body is coated in hydrophobic hairs, so as the spider is swimming around it’ll periodically poke its bum above the surface, trapping a silvery bubble of air that it carries around with it underwater.

  I know what you’re thinking. Another creature that breathes through its butt? What’s with this guy and animals that breathe through their butts? Well, I have good news, because spiders aren’t in this club. They do, however, breathe through their abdomen. The diving bell spider does it two ways. First, slits in the exoskeleton open into what are known as book lungs, so called because they have a series of plates, filled with hemolymph (the arachnid version of blood), that draw oxygen from the air and look like pages of a book. And second, holes in the exoskeleton allow oxygen to flow directly to organs and other tissues. With these two systems, the diving bell spider just has to keep air around its abdomen, leaving the mouth free to feed.

  This system comes in handy when the spider builds its namesake home. Swimming around all the time is dangerous and energy intensive, so the spider spins shelter between vegetation. Yet it doesn’t build out an expansive web like its terrestrial cousins, but instead a more spherical, hollow one—a bell. The spider need only make it big enough to insert its abdomen—though sometimes it’ll expand the nest to become big enough to move freely in—and it takes care to run lines to the surface that it’ll clamber up to grab more air and deposit in the bell. Thus can the diving bell spider live underwater indefinitely. And thanks to the laws of physics, it doesn’t even need to surface that often, maybe as little as once a day if it isn’t active much. This is because, just like at the surface of the water, oxygen is exchanged between the air and water through the web, so the oxygen the spider consumes is readily replaced.

  BUTTS: AN UNDERAPPRECIATED RESOURCE

  I once had an editor somewhat seriously suggest that I seek therapy for my proclivity for writing about animals that do weird things with their anuses. But it’s not my fault, really. It’s that a lot of critters do weird things with their anuses or, in the case of the pearlfish, with other critters’ anuses. I think this speaks to the larger issue of our anthropomorphization of the animal kingdom. Is it weird to us that pearlfish swim up sea cucumber butts and that there’s a species of leech that feeds only on the rectums of hippos? Sure, but the natural world has been humming along with such “eccentricities” for millennia. Or maybe I’m trying to justify not spending a bunch of money on therapy. Ironically enough, though, only a therapist could tell me that.

  Now, male and female diving bell spiders go about life a little differently. Males are far more active than females, which tend to hang out in their bells all day (they’ll also raise their young here, enlarging the bell as the youngsters grow). And believe it or not, these spiders are decent swimmers, especially the males, rapidly paddling their legs to propel themselves in pursuit of small fish and crustaceans like water fleas. The females, though, prefer to do their hunting at home, waiting for something to bump up against their webs, then scurrying out and attacking. But before they bring their prey in, they’ll enlarge their bells and grab more air. With a bit more room, they can then settle in to feed.

  These lifestyle differences could explain why males are bigger than females. That’s a bit weird, because as I mentioned earlier, such a size discrepancy simply isn’t the norm in the animal kingdom. But for spiders, this is downright goofy. In very few species do the boys grow bigger than the girls, because while females need to be big enough to bear a lot of young, male spiders focus on mobility. For spiders on land, being small helps them to get around: Some species, in fact, are so small that they can fly around by sending out a line of silk that the wind picks up, a trick known as ballooning. It’s so effective that sailors hundreds of miles out to sea have reported seeing flying spiders landing on their ships . . . so maybe it can be too effective.

  SOME SERIOUS MOMMY ISSUES

  Apart from the sexual organs, physical difference between the sexes of any given species is known as sexual dimorphism. This can be something like size, as in the diving bell spider, or ornamentation, as in the peacock and peahen. Perhaps the most astounding sexual dimorphism around is that of the Strepsiptera insects, nasty little things that invade the bodies of other bugs. A male looks fairly normal, almost like a fly, with wings and legs and all that. But a female is a glorified bag of eggs, with no eyes or legs or wings or even mouthparts. She invades a host and pokes her oviduct out of its abdomen, and a male comes along and fertilizes her. The young—up to a million (not a typo)—consume their mother from the inside out before erupting out of her and the host and into the world.

  But when it comes to mobility in an aquatic ecosystem, it pays to be bigger so you can more easily cut through the resistance of the water. Thus larger male diving bell spiders—which also have elongated front legs to aid in paddling—have a few advantages. For one, the better they can swim, the more likely they are to snag prey and avoid becoming lunch themselves. And keep in mind that dragging a bubble down from the surface is quite difficult, since the spider becomes much more buoyant when it’s carrying one. Size, then, equals power. Plus, the biggest, strongest swimmers will get access to more females. Hence natural selection favors larger male diving bell spiders, the opposite of their counterparts on land.

  Sure, moving into the water comes with its challenges. There are predators just as there are on land, and you have to somehow develop the ability to breathe underwater. But setting up shop in the new neighborhood also comes with a very important perk: The spiders get themselves a nice little niche, sitting there picking off those crustaceans. Diving bell spiders have left their fellow arachnids—their stiff competition—behind, and are now basking in an underwater monopoly. Think of it like moving from the mean streets into a secluded cabin. Only quite a bit wetter, I suppose.

  Zombie Ant

  PROBLEM: A fungus in a windless rain forest is going to have trouble getting its spores around.

  SOLUTION: Ophiocordyceps invades ants’ brains and mind-controls them up into trees to very specific spots, ordering the zombies to bite down on leaves before killing them. The fungus then erupts out of their heads and rains spores on their comrades below.

  You’re not going to buy a word of this. But here goes.

  The fungus spore begins by stick
ing to a carpenter ant’s exoskeleton, using enzymes to rot away the cuticle, all the while building up pressure to explode itself into the ant’s body. Here it reproduces over the next three weeks so prolifically that half the ant’s weight ends up being fungus. Meanwhile, the zombie ant is acting normally, shuffling around doing whatever it is ants choose to do with their day, while its comrades remain none the wiser to the fiend in their midst.

  Then the ant disappears. The fungus has ordered it to flee the colony around noon—always around noon. And it drives the stumbling and clearly unwell ant to a leaf ten inches off the ground—always ten inches off the ground. The fungus has found the perfect humidity and temperature with which to grow and, critically, it’s positioned itself right near one of the colony’s well-worn trails. The fungus orders the ant onto the underside of the leaf, where the zombie drives its mandibles into the vein, holds tight, and perishes. And with that, the fungus erupts out of the back of the ant’s head as a stalk, raining spores onto the trail below. Even if the fungus has steered the ant close to the path, but not directly over it, the stalk will grow at an angle that allows it to arch the stream of spores onto other ants on the trail. And multiple zombified ants can end up attacking a given trail, creating a snipers’ alley of sorts, picking off their erstwhile comrades and beginning the whole impossible freak show all over again.

  I’ve got this funny feeling you still don’t believe me, that the fungus, Ophiocordyceps, can orchestrate the world’s most startlingly complex parasite-host relationship, even though it doesn’t have a brain of its own. (The fungus is alone in this book in that it isn’t quite an animal and isn’t quite a plant, yet it behaves with the shrewdest calculations of the cleverest animals to create a unique creature: the zombie ant.) Or that the various species of the fungus specialize in attacking their own particular species of ant. But it’s happening. Every single day. And it’s been happening for a long, long time—scientists have found leaves 48 million years old that have the telltale bite marks of zombified ants.

  GROWTH INDUSTRY

  While carpenter ant colonies clash with mind-controlling fungi, the various species of South American leaf-cutter ants depend on another group of fungi to survive. Leaves in the tropics can be quite toxic, so these foraging ants don’t eat them. Instead, they saw off bits and carry them back to base. Here, other members of the colony chew the leaves up and spit them out for a fungus to dine on, and the ants in turn dine on the proliferating fungus. The problem, though, is that the promotion of fungal growth can let in a hyperaggressive mold. But not to worry: These ants are coated in special bacteria that check the invader’s growth, allowing the beneficial fungus to take hold and continue providing the colony with food, free of competition.

  Somehow the mindless fungus has figured out how to use ants as vehicles, likely because of a lack of wind in the forest to transport the spores. There’s too much dense vegetation. So in order to spread around, Ophio has evolved with the ants for millions upon millions of years—exploiting them, mind-controlling them—to distribute itself around the jungle. Really, that’s all quite embarrassing for the ants, which have built complex societies, only to fall victim to a mindless fungus. (Consider as an analogy your houseplants brainwashing you.)

  Scientists are only beginning to understand what’s happening to the ant’s body and mind during all of this, but we can say with reasonable confidence that it isn’t pleasant. What’s clear is that the fungus is producing neuromodulators, compounds that monkey with the ant’s neurons, which are of course responsible for coordinating movement. The fungus’s control, though, isn’t seamless. As the ant makes its way out of the colony, it convulses and collapses from time to time as the neuromodulators degrade its muscles. A lot like the way booze affects the human brain and coordination, so too does the fungus manipulate the ant, only much, much more precisely. The bug sways around as the fungus pulls the strings, guiding it to that exact spot where the stalk has the best chance of growing.

  Intriguingly, Ophio is related to ergot, the fungus that gave humanity LSD. Both fungi clearly have psychoactive properties, and both have found their way into the human psyche. On the Tibetan Plateau, for instance, there are related species of Ophio that attack different insects, though they don’t go through the sophisticated life cycle of the ant-zombifying varieties. And around 1,500 years ago some human caught on, noticing that yaks were gobbling up grass and some side dishes: ghost moth caterpillars with fungus stalks erupting out of their heads. The yaks would trip out, running around like a bunch of idiots. And just like that, a trade was born. These days the fungal caterpillars can sell for two thousand dollars an ounce and are said to make you good at sex.

  The Tibetan variety of Ophio is after caterpillars, but the ant-hunting variety faces a whole new slew of challenges with its host. You’ve probably been wondering why the hell the fungus would go through all the trouble to steer the ant around the rain forest when it has already infiltrated the colony, where there are plenty of other fresh bodies to corrupt. Well, among the many brilliant strategies of ants is their keen eye for misbehavior. If one of their own starts acting strange, they’ll drag it out of the colony and dump it in a nearby graveyard, because more than likely the thing has fallen victim to some kind of disease or, in our case, a homicidal fungus. This is known as social immunity, and it’s how ants avoid outbreaks that can wipe out whole colonies. But ant-exploiting parasites like Ophio have evolved alongside their hosts for millions of years and have come up with clever solutions. The same goes for the ant-decapitating fly. It knows that there’s no sense in sticking around the colony to get spotted. It steers its victim far away, where it can destroy the ant in peace.

  THE OPHIOCORDYCEPS ZOMBIE ANT FARM ACTION SET FOR SADISTIC CHILDREN OF ALL AGES

  For a long while scientists thought that mind-controlling fungi were more of a rain forest thing, but in 2009 the world expert on Ophio, David Hughes of Penn State, came across photos from a South Carolina woman who’d found them in her backyard. This variety is just as clever as its cousins, perhaps even more so. In the rain forest, leaves are there to bite onto year-round, but in South Carolina, there are of course seasons that strip trees of their foliage. As such, this North American fungus has evolved to command the ant to bite onto stems instead of leaves, since stems are available regardless of season. So take note: If you’re an ant you’re not safe in many places. Except maybe in an ant farm. That is, until someone comes up with the Ophiocordyceps Zombie Ant Farm Action Set for Sadistic Children of All Ages.

  Now if you’ll excuse me, I have a fortune to make.

  Are you still with me? Is this in any way believable for you? All I can do is insist that it’s happening, and that there are still many questions here. Why, for instance, doesn’t the fungus eventually wipe out the colony, leaving itself without vehicles to get to other ants? Part of the answer might be that these parasitic fungi have other parasitic fungi that exploit them, castrating the stalks after they erupt from the ants’ heads. But what about when something catastrophic happens, like outside forces decimating the colony? Can the fungus make the leap to another colony? Scientists still have much to learn, but we can say with confidence that ant zombification has been around for millions of years, with random mutation after random mutation allowing the fungus to assume a morbid mind control over its host.

  Pink Fairy Armadillo

  PROBLEM: Living in the desert means enduring brutally high and brutally low temperatures.

  SOLUTION: One burrowing armadillo has turned its protective shell into a blood-vessel-packed radiator that gives off extra heat or absorbs heat when needed.

  One of my biggest pet peeves is the characterization of the desert as “lifeless.” Nothing could be further from the truth. The desert is crawling with creatures—it’s just that so many of them, from insects to rodents to bats, only emerge at night, when the climate is bearable. But around the clock there’s a secret world that�
�s bustling beneath the apparent calm: that of the burrowers. And there’s no burrower more endearing, more charismatic, or more remarkable than the pink fairy armadillo of Argentina, one of the rarest mammals on Earth.

  Describing the pink fairy armadillo is an exercise in absurdity. The creature is cylindrical and can fit in the palm of your hand, sporting enormous claws that it uses to dig through the soil. Its body is covered with an almost perfectly white fur, topped with a pink band of a shell that stretches along its back, from its nose to its rump, which is flattened so as to tamp back soil as it burrows. All in all, it looks more like a torpedo than an armadillo.

  OUT ON A LIMB

  A couple thousand miles away from the pink fairy armadillo, in the deserts of Baja California, is another burrower that has also evolved a unique body shape to better move through the ground. Known as the Mexican mole lizard, it’s not actually a lizard but instead part of a unique group, amphisbaenia. The critter is long and thin like a snake, but has two front limbs it uses to dig. Yet it has no back limbs, save for some vestigial bones hidden away, so the Mexican mole lizard spends its days squirming and paddling those front limbs through the sand. Its name may not invoke the magic of the pink fairy armadillo’s, but hey, they can’t all be winners.

  As bizarre as it appears, the pink fairy armadillo is wonderfully adapted to subterranean life, so much so that it shuns the world aboveground. (You often hear the phrase “survival of the fittest” bandied around, which would imply that only physically strong species survive. In fact, those that are best adapted to their environment do. The armadillo isn’t as much physically “fit,” in the sense that it works out a lot, as it is well adapted, as we shall see.) Accordingly, humans almost never spot the armadillo. Conservation biologist Mariella Superina, for instance, hasn’t ever glimpsed one alive in the wild, and she’s the world expert in the darn thing. Scientists can’t even declare it endangered because there isn’t enough data to prove it. And while you might think that a life of such obscurity—hidden away from the desert’s burning days and freezing nights—would be nice and peaceful and cozy, it’s anything but.