The Wasp That Brainwashed the Caterpillar

by Matt Simon

  Yet the lowland streaked tenrec’s sonic modus operandi gets even weirder: Gould ran more experiments that showed the critters could be using echolocation to navigate. In a pitch-black room he placed a disk on a pole four and a half feet off the ground, and just below that another platform with a ramp that connected to a box containing a reward of food and water. He then assembled two groups of tenrecs, one that he outfitted with tiny earplugs and one without. Their goal was to drop down to the secondary platform and scurry to the reward box. The test subjects without earplugs did great. The others . . . not so much. Gould found that tenrecs with earplugs came to the edge of the disk to search for the platform far more often and spent far more time doing so, often missing the mark entirely when they made the leap.

  Yeah, they could have in part been sniffing out the location of the reward box, but this experiment showed that sound clearly plays a role in their navigation—and Gould got it all on a tape recorder. It turned out that the lowland streaked tenrecs weren’t stridulating to find their way around, but clicking their tongues, often in rapid succession. And not just on that platform: Gould noted that one enterprising little tenrec escaped in his laboratory, tongue-clicking as it scurried about. Thus, like bats, tenrecs appear to echolocate, sending out sound waves and listening as they bounce back to help build an image of the environment.

  And so our little tenrec mother, an unlikely master of sound, wanders the dark, perilous forests of Madagascar, clicking and stridulating her heart out as her kids amble nearby. But on the other side of the world in South America, there’s a toad that would be appalled at such irresponsible parenting. Because she prefers to hold her kids tight.

  Really tight.

  Surinam Toad

  PROBLEM: A pond, with its attendant predators, is a dangerous place for a tadpole.

  SOLUTION: Instead of leaving her kids at the mercy of the fiends, the Surinam toad mother embeds her eggs in her back and lets them develop under her skin, before the young erupt in unsettling fashion.

  The central irony in my life is being aware that as a biological entity, my sole purpose is to reproduce and pass along my genes, yet at the moment I haven’t the slightest desire to do so. And I’m in my early thirties. My younger sister has an adorable toddler, and I’m pretty cool with him. He even smiles at me sometimes. But what tends to keep me from having kids of my own is stuff like this: My sister once sent me a picture of my nephew in the backyard holding on to the lawn mower (he’s fond of such machines), butt-naked and with a turd behind him, looking over his shoulder at the camera with a knowing look on his oversized toddler noggin of: “Yeah, I just did that.” It seems that right before bath time, he’d caught sight of the apparatus out back and made a run for it. Holding on to the lawn mower, with the wind hitting his bare ass, he was apparently so excited that he lost his self-control. Which is all to say that perhaps picking up a kid’s doo-doo off the lawn isn’t on my short list of things to do in life.

  What a trifle that is, though, compared to the trials that the Surinam toad mom must suffer. She doesn’t lay eggs and leave them for predators to pick off. No, this toad will not part with her young so easily. After an underwater mating session of somersaults and egg laying with a male strapped onto her, the female’s fertilized eggs end up on her back, where skin grows around them, providing a cozy sanctuary for them to develop in before they erupt out of her en masse in what can only be described as a not okay thing for human beings to witness. (In her South American travels, Maria Sibylla Merian came across such an event. In one of her paintings from the expedition, a momma toad loaded with kids swims in a pond as a youngster that’s broken free trails behind. Next to them is a lovely plant and two shells, as if Merian is trying—and failing—to lighten the mood.)

  The husband and wife team of George and Mary Rabb published what is probably the most superb account of the somersaulting sexy time of the Surinam toad—if you can get past sentences such as “The ascent in the turnover was rotation about the longitudinal axis and in the descent they rotated transversely.” It all began on a spring night at the start of the swinging sixties in the Chicago Zoological Park. The lovers were two unnamed Surinam toads, who wished to remain anonymous, or whose names have simply been lost to history, or who perhaps were never given names in the first place because they were toads.

  TOADAL RECALL

  What’s the difference between a frog and toad? you might ask. To which I’d answer that I’m not sure. No one is quite sure. Toads tend to have warty, drier skin and shorter legs, but there are all kinds of exceptions. Really, it’s a problem of semantics: Animals didn’t evolve for us to place in categories. Toad or frog, frog or toad, it makes no difference to Mother Nature. The Surinam toad is so named because it lives in Suriname and it’s pretty toadish. And that, quite frankly, will have to do.

  The coupling began with a kind of mounting typical for frogs and toads, known as amplexus, with the male holding tight to the female’s lower abdomen with his forearms. For hours the pair did nothing but periodically swim up for air, at times rearing back into somersaults before they could break the surface. There were no sperm or eggs during all of that, but the researchers noted a “noticeable tumescent build-up of the female’s back skin.” She’d grown ready to accept the eggs, and finally, after the toads completed nine unproductive somersaults, George and Mary glimpsed the first egg stuck to the female’s back. The toads continued their flips, with the female laying three to five eggs at each somersault apex. At this point the eggs dropped onto skin folds on the male’s stomach, and he released his sperm to fertilize them. As the pair descended to right themselves, the eggs would drop onto the female’s back, where the male helped implant them with a bump of his belly. They somersaulted again and again, and at the end of their epic twenty-four-hour mating session, fifty-five eggs were embedded in her back, while only eleven had missed their mark and sunk to the bottom of the tank.

  When it was all over, the Rabbs removed the male and dropped him into another tank with more females. He tried his luck with them as well, but they rebuffed him. “While he was attempting to clasp the other females,” the Rabbs write, “the skin of his hind legs became loose and hung about them like ill-fitting stockings. The shedding proceeded over the entire body, and he ate the skin as fast as he could get it off in a grotesque sort of ballet.” They fail to mention, though, the grotesqueness that the female was about to endure.

  The swollen skin on the mother’s back starts to grow around the eggs, not entirely enveloping them, but embedding them snugly in a honeycomb pattern. They’ll develop there for several months, until they initiate one of nature’s more disturbing happenings. One by one the young toads—up to a hundred of them if the mating was good—begin to emerge. They haven’t grown into tadpoles at all, a rarity among frogs and toads known as direct development, but instead miniature versions of their mother, poking their skinny little fingers out of the holes in her back. As they squirm under her skin, sometimes all at once in a wave of twitching, every so often one pops out and swims away. And so they escape, tiny frog by tiny frog, until the mom is left with an empty nest and pockmarked skin that she eventually sheds. It’s a radical solution to the problem of predation, to say the least. But if any villains want to get at those kids, they’ve got to go through Mom first. Like, actually through her.

  THE PITFALLS OF SPECIES AND AUTOCORRECT

  Since I now can’t stop thinking about the limits of human language, this is as good a time as any to talk about the notion of a species. Agreement among biologists as to what exactly a species is can be such a problem that it’s known as the species . . . problem. Oxford Dictionaries defines a species as “a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding.” Yet there are all manner of hybrid species out there: a grizzly and polar bear, for instance, can come together in the wild to produce offspring. They’re different “species,” but are
capable of exchanging genes, which goes to show that we can do our best to make sense of the natural world, but in the end it’s an issue of language.

  Further semantic conundrums arise when scientists try to name “species” that are the product of “species” mating with other “species.” That grizzly/polar bear baby can be called a grolar bear or a pizzly, both of which I object to because my word processor tried to autocorrect them and therefore screwed up my writing flow, which I pray you didn’t notice.

  When the little Surinam toads head out into the big bad world, a world swarming with all kinds of dangers, it helps that they’re bizarrely flat to blend into the leaves at the bottom of their pond, spending their time splayed out among the sunken vegetation. Still, they’re vulnerable to predation and will be lucky to one day do sexual somersaults.

  But what if they had some kind of shelter? What if they could build a home? What if they made a home out of a sea cucumber’s anus?

  CHAPTER 3

  You Need a Place to Crash

  In Which Fish Swim Up Sea Cucumbers’ Bums and Birds Build Nests So Big They Pull Down Trees

  Shelter isn’t just a human pursuit. It can be nasty out there, with lots of teeth and claws and such things flying around. So certain enterprising creatures have hit upon solutions to the housing crisis. Birds build their nests, and ants dig their tunnels, but some animals opt to make their homes out of . . . other creatures. Hey, at least it’s always warm.

  Pearlfish

  PROBLEM: Fish don’t have many places to hide from their enemies on a barren seafloor.

  SOLUTION: The pearlfish swims up a sea cucumber’s anus, makes itself comfortable, and eats its host’s gonads.

  They say home is where the heart is, but for the pearlfish, home is more like where the gonad is. Because to find shelter it wiggles up a sea cucumber’s anus. And lives there. And eats its gonads.

  It all begins innocently enough. The skinny, eel-like fish approaches the sea cucumber and gives it a sniff, moving up and down the length of its soon-to-be victim with its body pointed almost vertically. It’s looking for the sea cucumber’s breath, because, well, sea cucumbers breathe through their derrières. If the sea cucumber detects the pearlfish, it’ll hold its breath, sealing its butt like a human holding in a fart. But the sad sack is only delaying the inevitable. At some point it has to breathe, and that’s when the pearlfish strikes.

  Once the pearlfish sees its window of opportunity, it has to make one of the toughest decisions in the animal kingdom: whether to enter the sea cucumber’s bum tail first or head first. This, of course, all depends on the size of the orifice (called a cloaca, since it’s used for not just waste removal but also reproduction and breathing). If the opening is big enough to enter head first, the pearlfish goes at it full tilt, jamming its face in and rapidly flicking its tail to fire itself into the sea cucumber. If the opening is too small, the fish first inserts its thin tail, then backs in slowly. And because they’re so much smaller, juvenile pearlfish will go in head first 80 percent of the time, whereas adults go in tail first 80 percent of the time (yes, someone calculated that).

  You wouldn’t blame the pearlfish for not wanting to hang out in its host’s intestines. So instead, once the fish is in there it wiggles into what’s known as the respiratory tree, which branches out as tubes on either side of the sea cucumber’s intestines. The sea cucumber breathes by pumping water in and out of its cloaca and into the tree. So not only is the pearlfish enjoying shelter while it’s in there, it’s getting a constantly replenished source of water, and therefore oxygen.

  Some species of pearlfish are content sitting there biding their time, safe from predators circling above. Others . . . they get a bit hungry. They’ll start feeding on various parts of the sea cucumber, including the gonads, which isn’t as bad as it sounds. Well, I don’t think the sea cucumber particularly enjoys the gesture, but once the gonads are gone it can grow new ones. The same goes for its other organs: The critter is a remarkable regenerator. But it can find itself overwhelmed with enemies, and while it can regrow the bits one pearlfish has eaten, another is bound to show up and hack away at its insides once again. In fact, a biologist once found fifteen pearlfish in one poor bastard of a sea cucumber.

  WHY YOU’LL NEVER MEET A SEA CUCUMBER DENTIST

  Sea cucumbers aren’t entirely defenseless against the onslaught of the pearlfish. Certain species are equipped with calcified projections known as anal teeth, which are shaped like cones. They all point inward toward the center of the anus, looking a bit like the doors they have in sci-fi movies that don’t swing or slide open but open up from the center out, as a camera shutter would. These may well have evolved specifically to help keep pearlfish out, which goes to show that at least a few kinds of sea cucumbers find it less embarrassing to have teeth in their bums than having their gonads eaten.

  And if you thought the fish were ignoring each other’s advances in there, you’ve got another thing coming. Pearlfish also get busy in the respiratory trees, the ultimate indignity after the sea cucumber has itself been sterilized. This sort of thing is not uncommon: A lot of parasites sterilize their hosts, and it makes good sense. It takes a tremendous amount of energy and resources to reproduce—remember the lengths the flatworm goes through to avoid bearing young. If a parasite can figure out how to sterilize its victim, that means more energy is available to support its own shenanigans. Whether sterilization is the pearlfish’s strategy or the gonad happens to be tasty isn’t yet clear. Could be both, really. You’d have to ask a pearlfish.

  Now, while we use shelter more to protect our relatively hairless and fragile bodies from the elements, other creatures, including any number of burrowers, use shelter to avoid predation. The pearlfish is doing the same thing, really, only it’s burrowing up sea cucumber cabooses. You have to consider that the seafloor is a very dangerous place indeed. It’s not all intricate coral reefs out there, with plenty of hiding places like caves and crevices. Much of the ocean is featureless stretches of sand.

  And pearlfish don’t limit themselves to taking up residence in sea cucumbers. Some species instead invade sea stars, and still others go after bivalves like oysters. Those strategies would appear to be better options, considering the sea cucumber itself is vulnerable, on account of being essentially a tube of meat wandering along the seafloor. But while it may look appetizing, in reality, it’s not, for the sea cucumber has a secret weapon: It disembowels itself to scare away predators.

  SUFFERING FOR FASHION

  Pearlfish are called pearlfish because folks will pop open oysters and find the fish covered in the beautiful material that the mollusk would typically use to form a pearl—a nice fashion accessory if the fish weren’t too dead to enjoy it. (Any pearl, by the way, is a shelled mollusk’s defense against a foreign object that has infiltrated it. By coating the invader, the mollusk isolates and neutralizes it.) Researchers have found that when these fish are actually alive in there, they’re rapidly vibrating their swim bladders, like the toadfish, to call to their compatriots swimming out in the open. It might seem like the inside of an oyster wouldn’t be great for acoustics, but in fact the shell amplifies the frequencies the fish are calling at. So it’s like a microphone. That you live in. And probably isn’t too happy with you.

  Admittedly that doesn’t sound like an effective defense at face value, but hear me out. When a sea cucumber feels threatened, the connective tissues that hold its organs in place soften in an instant. Depending on the species, the body wall around either the mouth or the heinie also softens. With everything loosey-goosey, the sea cucumber contracts its muscles, firing its guts through the weakened body wall at one end or the other. And it isn’t just the intestines that take these explosive little field trips. Sometimes even parts of the respiratory tree and, yes, the gonads can go, too (it seems that there are few jobs in the animal kingdom as thankless as that of the sea cucumber gonad). There a
re some species that have evolved an even more potent defense, ejecting toxic tubes out of their anuses along with the guts. The explosion is a kind of surprise that maybe, just maybe, is weird and smelly and goopy enough to scare away predators. And as traumatic as it all sounds, sea cucumbers can regenerate the lost organs in a few weeks.

  Interestingly, the pearlfish doesn’t seem to trigger these defenses, and as yet no one is quite sure why. Maybe it’s more energetically cost-effective for the sea cucumber to deal with regrowing gonads than the intestines and all the other ejected bits. So what the pearlfish ends up with is a living, breathing mobile home, which staves off attack by dropping its guts out, like a James Bond car deploying caltrops to slow pursuers. Except the sea cucumber isn’t going to get the girl. You know, on account of missing its gonads.

  Tongue-Eating Isopod

  PROBLEM: Floating around in the open sea is perilous (just ask the ocean sunfish).

  SOLUTION: A certain crustacean swims into a fish’s mouth and doesn’t stop there—the tongue-eating isopod didn’t get its name for nothing.

  Living in a sea cucumber and eating its gonads is nice and all, but what if you’re looking for a place with more of a view? Perhaps where you can experience the big blue ocean in all its glory? You’d think the luxury would come at a price. But no, on the contrary. If you can manage to find a place like this, you’re going to get away with murder.