The Wasp That Brainwashed the Caterpillar

by Matt Simon

  Boy, that Ernest. Always riled up about something.

  To our eyes such scenes are brutal, but this is how life works, a rather grim illustration of Charles Darwin’s 1859 theory of evolution by natural selection. That by natural selection bit is important, because naturalists in Darwin’s time had already been kicking around the idea that species change, though they usually referred to this as “transmutation.” Darwin’s society-shaking revelation was the mechanisms involved: Species typically produce more offspring than can survive, these offspring vary in their characteristics, and those with variations that better suit them to their environment survive to breed and pass those “good” genes along. This is how a species evolves, adapting to its environment and predators. And necessarily a whole lot of maladapted creatures must die in the process.

  Antechinus blokes, for their part, don’t seem to mind it. They’re simply living out the meaning of life: get laid at all costs, even at the expense of their own well-being. And really, females live for only a few years, so your regular Joe Schmo Antechinus doesn’t have much to lose with his suicidal plunge into fatherhood (not a single one of them makes it past his first birthday, since they were all born after the previous mating season). He’s mated with dozens of females, and ideally at least one of them will bear his young. Meaning of life achieved, he slips into darkness as the females prepare to do the real work.

  Anglerfish

  PROBLEM: Think finding love in a bar is hard? Try finding it in the desolation of the deep sea.

  SOLUTION: When the diminutive male anglerfish finds a lady—who can be five hundred thousand times heavier than him—he doesn’t let her go. He bites onto her, fuses his face to her tissue, and lives the rest of his life releasing sperm whenever she beckons.

  Let us not mourn poor antechinus, for there’s an hombre down in the ocean depths that doesn’t have it so easy as death by sex. This one lives his life in sexual servitude, and not even the good kind. I’m talking about the freakish, not-at-all-fun existence of the deep-sea anglerfish.

  You’d be forgiven for thinking that the females and males of the 160 or so species of deep-sea anglerfish were different animals. The females are stunning. First and foremost, they have a bioluminescent lure that dangles in front of their faces to attract prey as well as mates, with species utilizing different lure shapes and flashing routines so the roaming males of their respective kind can tell them apart. They’ve got giant teeth attached to giant mouths so they can be sure to consume whatever rare prey they happen upon in the desolation of the deep, as well as cavernous stomachs that allow them to digest such meals. And indeed the many species of anglerfish differ quite remarkably in their shapes and sizes. Some are more streamlined, while others are comically spherical stomachs with faces, forsaking all that “speed” and “maneuverability” for the life of a swimming softball.

  Sometimes female anglerfish have tiny lumps on their bodies that appear to be parasites latched on for a free meal. These are parasites, all right, in their own way, at least: They’re actually small male anglerfish, so small that in some species the fellas are among the world’s smallest vertebrates (that is, creatures with a spine, as opposed to invertebrates, which lack a spine). These lucky males have fulfilled what is their only function in life: to find a female, which can weigh five hundred thousand times more than them. In fact, males are unable to feed, and they set out from birth to find the elusive females down in the darkness. Yet only an estimated 1 percent of males ever succeed. The rest die of starvation. But should they be able to sniff out a female—using the biggest nostrils relative to head size in the animal kingdom—they’ll latch onto a lady with their pincerlike teeth, and the pair will live out the rest of their lives as one.

  LIGHT OF MY LIFE

  Perhaps 90 percent of life in the deep oceans utilizes bioluminescence. This would seem to be somewhat of a detriment to survival, what with being lit up like the Fourth of July down there in the dark for predators to see. But bioluminescence is an indispensable tool for a number of reasons. Beyond its usefulness for communication and luring, as we see in the anglerfish, creatures can also use it as a defense system: Some species of shrimp eject a cloud of glowing goo to confuse attackers like an octopus ejects ink. Others use bioluminescence to light up their bellies to match what little light is coming from the surface, breaking up their silhouette for predators watching below. And still others employ what is known as a sacrificial tag: If a predator eats part of their glowing body, and that predator is transparent (which happens to be in vogue down there), they’ll keep on glowing in its stomach. This makes the predator suddenly the conspicuous prey, like a bank robber marked by an ink bomb.

  Here’s how it works. After the male has latched on, enzymes begin to break down his face, welding him to the female. He’ll grow considerably larger by tapping into the female’s circulatory system, which will provide him with nutrition, while unnecessary organs and structures like the eyes atrophy away. Because he’s stealing nutrition from her, he’s technically a parasite, and in fact this is known as sexual parasitism. That’s right, anglerfish are parasites of . . . themselves. (The males of some species, though, are fortunate enough to forgo the fusing: They attach, take nutrients from the female and release some sperm, then detach and go on their way.)

  The charming couple also syncs hormones, so the female can trigger his sperm release when she releases her own eggs, great thirty-foot-long sheets of them that soak up his seed. (Because the male is providing something to the female—that is, sperm—some biologists might argue that he isn’t technically a parasite. So the anglerfish relationship is complicated, to say the least.) The female has become, in effect, a self-fertilizing hermaphrodite. Over her thirty-year lifetime, she may collect several of these males, all of which keep producing sperm until she dies and the whole weird amalgam sinks down into the abyss.

  This rather inventive solution to the problem of finding regular sex has the added benefit of turning the anglerfish into a baby-making machine, churning out as many eggs and sperm as her energy levels allow. That’s why female anglerfish so dwarf their male counterparts: It’s all about the gametes—the eggs and sperm. Human males tend to think that their size grants them some sort of superiority over women, and that the same must be universally true in nature, but in most species the females actually grow larger than the males. That’s in part because females must put a ton of energy into producing eggs—the lady anglerfish has such a giant mouth and stomach because she lives where there are so few things to eat, and therefore needs to be sure to tackle whatever comes her way to procure the energy. Eggs also take up far more room than sperm, so the male can afford to be comparatively tiny.

  Elsewhere in the animal kingdom, eggs are so precious that females are quite picky about who they mate with because they can only produce so many gametes. They shack up with only the best dancer or scrapper, for instance, to be sure they’re choosing strong genes to pass down to their kids. And when animals like mammals do get knocked up, they have to put even more energy into raising the little rug rats inside their bodies. Such pickiness leads to intense competition between males for the right to mate, which can result in some species flipping the size norm: Males grow bigger than females in order to compete among themselves for the ladies’ affection.

  The female antechinus and anglerfish, though, have evolved to “choose” the best-adapted males in their own subtle way. The former makes her counterparts grow big testicles while the latter is very elusive—remember that all but 1 percent of male anglerfish perish before finding a mate. But that’s not for lack of trying. It’s just really, really hard to track down a female in the vast blackness of the deep. Only the best, master-lady-tracker males have the chance of fusing to females and passing along their genes to the next generation. This is probably why over evolutionary time the males’ mate-sniffing nostrils grew so big, for such a trait wins them the right to pass down their ge
nes for a large schnoz.

  “FEMALE PENIS, MALE VAGINA, AND THEIR CORRELATED EVOLUTION IN A CAVE INSECT”

  A notable exception to female pickiness of mates is the Neotrogla genus (that is, a group of closely related species) of insects in Brazil, whose ladies have the penis and males have the vagina. Well, technically the females have a penislike structure, which they use to penetrate the male’s sperm duct to grab his seed and a nutritious little package known as a nuptial gift, providing her invaluable energy in the barren caves they inhabit. Thus females have evolved to become the pursuers while the males play hard to get. The paper announcing their discovery, by the way, was intriguingly titled “Female Penis, Male Vagina, and Their Correlated Evolution in a Cave Insect.”

  It’s no wonder that these weird goings-on confused the first naturalists to observe attached males in the early twentieth century, scientists who originally thought they were seeing larvae fused to the females. But when the truth emerged, confusion turned to shock, which then gave way to horror. In 1938, William Beebe, the great naturalist and explorer, summed up the anglerfish zeitgeist of the day best:

  To be driven by impelling odor headlong upon a mate so gigantic, in such immense and forbidding darkness, and willfully to eat a hole in her soft side, to feel the gradually increasing transfusion of her blood through one’s veins, to lose everything that marked one as other than a worm, to become a brainless, senseless thing that was a fish—this is sheer fiction, beyond all belief unless we have seen the proof of it.

  So you keep swimming around furnishing that proof, little anglerfish sir. And you keep being you.

  Flatworm

  PROBLEM: Being a mom is a huge responsibility.

  SOLUTION: Hermaphroditic flatworms penis-fence, of course. Individual flatworms have both sperm and eggs, so whichever worm stabs its partner with its needle-like genitals wins the honor of not giving birth, while the fertilized loser mopes away.

  As we’ve seen with the anglerfish and antechinus, males typically have to put in the effort to get laid, but the true biological burden lies with the female, who expends enormous energy producing eggs and, in the case of mammals, bearing and looking after the young. But what if you’re a hermaphrodite, like some species of marine flatworms? Who’s going to bear the maternal burden there?

  Whoever loses the bout of penis fencing, that’s who. In coral reefs, far away from the depths where anglerfish have their own weird sex, certain species of flatworm do battle with their members.

  It starts off innocently enough. Two often brilliantly colored flatworms approach each other and nuzzle a bit. But before long the calm departs, as each rears up and exposes its weapons: the two sharp white stylets that are its penises. Like human fencers, each flatworm will juke and stab, simultaneously trying to inject its partner with sperm anywhere on its body while doing its best to avoid getting inseminated itself. And this can go on for as long as an hour until the two retract their double penises, lower themselves, and go their separate ways. When the struggle is over, both can end up pockmarked with white stab wounds filled with sperm, and you can see pale streaks running along their bodies, branching rivers of semen on their way to fertilize the eggs.

  ANYTHING CAN BE A WORM IF IT PUTS ITS MIND TO IT

  As far as the English language is concerned, a worm can be just about anything, within reason, of course. If you’re elongated and don’t have a spine and are kinda squishy, chances are you can pass as a worm. So this includes the many-legged velvet worms (we’ll meet them later), the tapeworms that invade our intestines, and the earthworms, which in Australia grow to six feet long (leave it to Australia, the Land of Generally Ridiculous Beasts). That length is laughable, though, compared to the marine bootlace worm, which has been known to grow to one hundred feet long—the length of a blue whale, the biggest creature ever to grace planet Earth. One specimen found in Scotland was even said to measure in at 180 feet, though its handlers—perhaps chasing that ever-elusive title of “Discoverers of the Longest Creature on Earth”—likely stretched it out. Fame does weird things to people, you know.

  Now, you might be asking why. Why evolve violent “traumatic insemination,” or more specifically and hilariously, “intradermal hypodermic insemination”? The problem is that the two flatworms have the same interest: Neither wants to be the female (I know that sounds sexist, but bear with me here). Developing those eggs is a tremendous energy suck, not to mention that the loser is deeply wounded on top of being knocked up. The winner gets to pass down its genes without taking the trouble of raising the young.

  But here’s the weirdest part. Natural selection dictates that if the tapeworm’s going to get stabbed, it’s in its best interest to get stabbed a whole lot. The most accomplished fencers are the ones who will have the most reproductive success, and their genes are what other flatworms want to pass down to their offspring, who will in turn be more likely to become skillful combatants and fertilizers. It’s one of nature’s cruelest ironies: The flatworm doesn’t want to be stabbed with a penis and inseminated, but if it must, it may as well get stabbed with a penis and inseminated thoroughly.

  Things get even weirder with another type of flatworm, this one a transparent, microscopic species. It, like our beautiful seafloor variety of flatworm, mates by injecting its partner with sperm. But it seems that the tiny flatworm can really feel the pangs of loneliness: If there aren’t any partners around, it uses its stylet to stab itself . . . in the head, a maneuver known as selfing. The stylet is at the tail, while the head is of course at the other end, so with a dexterous bend the flatworm can jab itself right in the noodle. The sperm then makes its way down the body to fertilize the eggs. So in a pinch, the flatworm can reproduce all on its own. The researchers who discovered the behavior cautiously referred to it as hypodermic insemination, not traumatic insemination (as in the aforementioned fencers), because they weren’t sure if the creature seriously injures itself with the stab to the head. Not even kidding here.

  Now, flatworms aren’t the only creatures out there engaging in such shenanigans. Far from it. In case you needed another reason to fear/despise/be grossed out by bedbugs, they’re reproducing by traumatic insemination in our sheets. A male will puncture a female’s exoskeleton with his genitalia and pump his sperm into her body cavity—no trifling matter when bedbugs rely on their tough shells to protect them from the elements. Indeed, female bedbugs have evolved an immune response: proteins that erode the cell walls of bacteria, helping them ward off infection.

  Such is the push and pull in the battle of the sexes. As one side evolves an attack, the other evolves a defense, nature creating problems and then solving them. The issue comes right back down to the meaning of life: reproduce at all costs. This can put the sexes in conflict with each other—or, in the case of the tapeworm, the single hermaphroditic sex in conflict with others of the single hermaphroditic sex—particularly when females need to maintain some measure of control over who they mate with to ensure they’re picking the best genes. And perhaps nowhere is this kind of sexual conflict more dramatic than among ducks, whose males are notoriously forceful with their mating. Females have evolved a vagina that corkscrews to try to keep out the male’s penis, which corkscrews in the opposite direction (and can grow up to fifteen inches long). Some duck vaginas even have pockets that branch off into dead ends, frustrating the male’s efforts.

  The idea that animals can be choosy about their mates, and that such choosiness will drive the evolution of certain characteristics, was one of Charles Darwin’s more brilliant realizations. Known as sexual selection, it drew ridicule in Victorian England, a patriarchal society that found the notion of female choice laughable, to say the least, especially when it came to sex. A notable dissenter, though, was none other than Alfred Russel “So What If It’s Only One ‘L’” Wallace, the phenom naturalist who had simultaneously developed the theory of natural selection on his own. (Charles Darwin scrambled to pub
lish On the Origin of Species after receiving a letter from Wallace, an acquaintance who would later become a good friend, pontificating on his ideas. But that was only after colleagues presented the ideas of both men to the Linnean Society of London.) Wallace didn’t think animals had the brainpower to make these choices, except when it came to the ladies of our own species. He wrote that “when women are economically and socially free to choose, numbers of the worst men among all classes who now readily obtain wives will be almost universally rejected,” thus improving the species. Emphasis his own.

  Gotta love that feminist optimism, however wrong he may have been about sexual selection. (To be clear, Wallace was brilliant, so perhaps this isn’t the greatest way to introduce him, and for that I apologize. But we’re all wrong sometimes, and indeed being wrong is fine in science, for it invites others to discover the truth. We’ll see more of Wallace in the next chapter being very right.) Females in the animal kingdom can in fact wield great power when it comes to sex.

  THAT TIME WHEN FOX NEWS AND DUCK GENITALS COLLIDED—NOT LITERALLY, OF COURSE

  One scientist who studies the duck genital arms race, Patricia Brennan, came under fire in 2013 when conservatives discovered that she received federal funding for her research, through the National Science Foundation. It seems that at the time a Fox News poll found that 89 percent of its website readers/TV viewers considered the study of ducks’ naughty bits to be a waste of their tax dollars. Brennan defended herself in a Slate op-ed, noting that it was actually during the Bush administration in 2005 that the government first gave her money. “The fact that this grant was funded,” she wrote, “after the careful scrutiny of many scientists and NSF administrators, reflects the fact that this research is grounded in solid theory and that the project was viewed as having the potential to move science forward (and it has), as well as fascinate and engage the public.”