Wild Things
Slate’s animal blog.

Sept. 1 2015 12:13 PM

Animals That Scientists Thought Never, Ever Have Sex Actually Do Have Sex

This article originally appeared in Sick Papes, a blog about exciting new science papers.

As all you puddle-suckers know, there are entire universes of microscopic organisms living in every drop of puddle water, moss moisture, and sidewalk juice. Indeed, it was within a drop of filthy gutter scum that Antony van Leeuwenhoek (1632–1723) observed single-celled and other microscopic organisms for the first time. He also provided the first microscopic drawings of human sperm, which lead to some great drawings of little tiny men scrunched up inside the head of a sperm. [Editor’s note: this man-in-sperm theory is no crazier than the truth of how humans develop.] The revolutionary nature of Leeuwenhoek’s observations are even more impressive considering how shitty the microscope that he used was: Made of a single hemisphere of glass fixed to a metal plate, these scopes had a fixed focal distance of about 0.5 millimeters but magnified up to 275 times, and apparently had a resolution approaching one micron.


Today’s Sick Pape focuses on one of the types of animals that Leeuwenhoek saw when he magnified a drop of water: rotifers. Rotifers are microscopic animals (not bacteria, not amoebas—multicellular animals) measuring between about 100–500 microns yet possessing a complex anatomy including a nervous system and a digestive system. And for the past two decades, rotifers in the genus Bdelloidea have been the subject of intense research for one reason: They never, ever have sex.

Sexual reproduction is thought to be essential for the long-term survival of a species. There are a handful of animals that will occasionally pop out a virgin birth, but this is typically done just for a ratings bump at Animal Planet during the holiday season. In general, there are no species that exclusively reproduce asexually and manage to last more than a few million years. While there may be short-term Darwinian benefits to cloning yourself, only sexual reproduction can provide the cosmic intermingling and chromosomal diversity that organisms need to survive the long evolutionary grind.

Bdelloid rotifers thus pose a major question: How has this species survived for hundreds of millions of years without ever having sex? Male bdelloid rotifers have never been observed, nor has anyone ever witnessed meiosis or mating. Instead, the females just happily clone themselves forever like a goddamn metaphor I can’t think of right now. The big question has always been: How come these ladies haven’t gone extinct? What’s their secret?

Over the past few decades, bdelloid rotifers have been whispering their secrets into the quivering ears of Matt Meselson’s lab. Meselson is one of the best scientists who has ever lived, responsible for “the most beautiful experiment in biology” as well as helping to discover mRNA and many other Old Testament breakthroughs (as well as crusading for years against biological weapons). Which is just to say, he knows what the funk he’s talking about. And his lab has shown that bdelloid rotifers have a variety of alien mechanisms for increasing their genetic diversity without having sex. Namely, these rotifers suck up random DNA from their surroundings and shove it into their own genomes, and they also shatter their entire genome and then rebuild it with errors.

And now, Meselson (who is currently in his 80s) and his lab have done something that is so rarely done these days: They have provided strong evidence that their entire premise was wrong and that bdelloid rotifers actually do reproduce sexually. I want to emphasize that none of their past research was wrong; each of their past experiments still hold up, all the crazy DNA-sucking-and-shattering is still real, it’s just that these strategies exist in addition to sex (albeit, very infrequent sex).

Meselson and his squad begin their Sick Pape with an ominous threat that would terrify the Edward Snowdens and Chelsea Mannings among us: “Certain methods … offer definitive means for detecting infrequent or atypical sex.” [Editor’s note: What you or I do in private is not the business of the Meselson lab or the state.] However, instead of using the CIA interrogation methods implied by this terrifying abstract, they stick to modest and routine population genetics strategies. Specifically, these folks test for patterns of genetic similarity between different rotifers that imply they are the product of sexual reproduction in the not-too-distant past, and they find it.

For those who want to come into the methodological weeds with me, the “certain methods” to detect infrequent sex is this: You sequence a few genes from each of several rotifers and then look for a pattern where Gene X from rotifer 1 is very similar to its homolog in rotifer 2, whereas Gene Y is similar to its homolog in rotifer 3. This implies that there has been recent sex that has jumbled up different chromosomes between individuals in the population. To be sure that this wasn’t the result of direct DNA transfer between rotifers 1 and 3, these auteurs do the same test at several genes and show that the same pattern holds for all these genes, making it very, very unlikely to have been direct horizontal transfer of DNA.

We honor Ana Signorovitch, the pape’s first author, and her colleagues in the Meselson lab for having the courage to disprove themselves—an uncommon mark of high integrity—and for shining their beautiful light on an invisible little corner of our world. Of course, the timing and mechanisms of sex remain a complete mystery, so please keep up the hard work for many more decades to come!

Signorovitch, A., Hur, J., Gladyshev, E., & Meselson, M. (2015). Allele Sharing and Evidence for Sexuality in a Mitochondrial Clade of Bdelloid Rotifers. Genetics. doi:10.1534/genetics.115.176719

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Aug. 27 2015 2:00 PM

Define “Rational”: Is That a Decoy or Your Frog Prince?

“Irrational mate choice” sounds like an accusation my mother might level at me in a terse email subject line, but in this case, it’s the title of a paper on sexual selection in the Panamanian túngara frog (Physalaemus pustulosus) published Thursday in Science magazine. In the paper, behavioral ecologists Amanda M. Lea and Michael J. Ryan report for the first time that female túngara frogs don’t always act rationally when it comes to mating—a finding that could challenge our simple understanding of this kind of mating system.

“This is the first time we’ve found evidence for irrational mating behavior,” says Lea. “If they aren’t making rational decisions, then these models don’t hold up.”


Keep in mind that, in evolutionary biology, rational doesn’t necessarily mean governed by reason (and irrational doesn’t always mean face-palmingly naive). Rather, a rational mating choice is one that conforms to an evolutionary system by which females choose their mate based on his ability to maximize her Darwinian fitness. In the animal kingdom, we expect animals to make these choices as simply, efficiently, and consistently as we choose the best value in off-brand oatmeal.

Yet in the new study, inferior suitors known as decoys—male frogs with less appealing voices and a slower call rate—threw a wrench in the whole “rational system” hypothesis. These decoys snuck into a group of displaying male frogs, thrusting themselves near the better options and throwing off the females’ focus. Weirdly, their presence caused the ladies to switch their initial decisions and instead go for a nearby male with a slower—less appealing—call. Talk about a bad morning after.

One explanation for the switcheroo is that female túngara frogs are easily flustered. (Decoys aren’t the only ones known to have deceived them: “I have to tell you," says Lea, "I’ve attracted many female frogs making these calls.”) You can hardly blame them. Choosing an amphibious amor is already complex enough, what with all the swelling, foaming, ribbitting, and whatnot. Adding another male to the mix, researchers speculate, could overload the female frog’s cognitive resources and cause her to make a mistake. (This confirms my opinion that grocery stores should only stock one of every option.) 

Or the mix-up might be more sinister. Decoys may intentionally create a confusing comparison, taking advantage of the kind of logic used in cognitive tests where people can’t tell that two circles are the same size because of the differently sized circles surrounding them. Similarly, dating is about comparison; the appeal of one prospect changes depending on what’s around him. With the decoy around, the female tends to prefer whatever other male is closest to it—even if he isn’t the most attractive option of the three. Think of him as a particularly ugly wingman: Next to him, the guy sitting next to him suddenly doesn’t look so bad. 

“I used to be a bartender, so this is all very familiar,” says Lea, who likes to compare her study species to human males showing off at a bar. A more modern comparison might be the world of online dating, where individuals casually scroll through prospective mates, comparing each one’s profile picture and vital stats to the one that came before it. “If the past 10 are all really really bad, you might just start to lower your threshold,” Lea says.

“I’m actually surprised no one has looked at that,” she adds. “Someone should do that study.”

The inevitable question: What’s in it for the decoy? It could be that he and the other male are engaging in a mutually beneficial friendship, whereby each takes turns acting like an inferior male to give the other a mating boost (frog bros?). In that case, they would probably be genetically related (actual bros!), so that boosting each other’s mating success would also be helping to support their own gene pool. But Lea thinks there is a likelier—and sadder—reason. 

Perhaps the decoy has no choice. After all, like the peacock, the túngara frog is a species in which the male’s sole purpose is to mate. True, even if he keeps calling, he’s probably not going to get a mate. But if he doesn’t call at all, then he definitely won’t. So no matter how spindly, how unattractive, or how woefully inadequate he may be, the decoy is doomed to just keep calling, and calling, and calling—even when there’s no one there to answer. “I’ve seen these guys die in the field mid-call,” says Lea sadly. “He’s just doing the best he can.”

Aug. 20 2015 2:02 PM

Eat the Young

In 1729, satirist Jonathan Swift proposed a sweeping solution to Ireland’s conjoined horrors of poverty, starvation, and overpopulation: Eat Irish babies. (1-year-olds, he surmised, would be equally tasty either roasted whole or baked into a pie.) Since then, murdering the youth has generally been a bit hard to sell as a social good. Yet according to ecologists in a paper published Thursday in Science, that’s exactly what we should be doing when we prey on other species.

Ecologically speaking, the role of modern humans as predators is unique: We’ve increased our killing capacity exponentially through symbiotic hunting with dogs, ever more effective weapons, and the use of fossil fuels for energy. But when researchers surveyed nearly 2,200 species across 6 continents, they found that one difference had particularly dire environmental consequences: We eat adults instead of juveniles. As a result, we tear apart food webs that have evolved over millions of years and shrink the number of animals available for human consumption in the long term.


Look at the rest of the animal kingdom, and you’ll see just how weird a strategy this is. In general, predators tend to feed on juveniles and the old or sickly; after all, they’re the easiest to catch. For instance, co-author and University of Victoria ecologist Thomas Reimchen found that predatory trout and loons in remote Canadian lakes dined almost exclusively on the juveniles (or fry) of their prey, the stickle-backed fish, while eating less than 5 percent of the adults. This strategy allowed the stickle-backs to remain at stable, healthy numbers.

By contrast, humans mainly hunt mature animals; after all, they’re larger and easier to process. Researchers found that marine fisheries take in a median rate of 14 percent—but up to a whopping 80 percent—of the biomass of adult fish. (While the fisheries example is the most dramatic, similar trends came up when they looked at data on hunting wildlife and tropical wild meat spanning back to the 1990s.) These modern practices “are especially stunning and underline just how peculiar a predator the human species has become,” says Chris Darimont, a conservation scientist at the University of Victoria and lead author on the study.

To understand why we should care about how old our prey is, it helps to understand a little more about the reproductive cycle of a fish. As fish age, they grow more fecund. And we’re not just talking about spawning one or two more eggs—adult herring can spawn hundreds of thousands of eggs a year. (Fish parents should be grateful they don't have to send their spawn to college.) Most, sadly, “are doomed from the moment they were born” due to starvation, predation, etc., says Darimont. Yet if you spawn enough, a few will, with luck, survive.

What that means for predators is that it’s generally fine to chomp up some of the plentiful wee ones. Even consuming 5 to 10 percent of those offspring—the median for most predators, according to the study—leaves plenty who will go on to become fertile adults and ensure the survival of the species. The researchers make an economic analogy, referring to the offspring as “reproductive interest” (that is, they are essentially extra, and expendable) and the adults as “reproductive capital” (the thing you want to invest in and not deplete, because they’ll make you more and more “interest” over time). Eat only the interest, and predatory cycles remain sustainable over the long term.

But that isn’t what humans do. In fact, our current ecological paradigm runs pretty much the opposite of this idea: We save the youth at the expense of the adults. Some environmental policies actually fine fishers who don’t throw juveniles back in the ocean, when those are the very fish we should be targeting. While our intentions were good—fisheries managers thought that the tossed-back small fish would then have a chance to grow up to be big fish—our predation is totally out of sync with actual ecological logic.

That isn’t the only way we’re out of sync, of course. Humans are the only species to have taken our killing to industrial levels: To feed the appetites of those across the globe, we take far more than we need, and freeze millions of pounds of seafood at sea. We ship salmon caught in Alaskan waters to New York, and fish caught in African waters to France. We engage in practices like poaching and hunting large game, making us the only predator to disrupt food chains by turning other large predators into prey. And the dark side of our mass hunting goes beyond the ecological: Fishery exploitation has led to piracy, child labor, and even slavery on fishing vessels.

So we should kill fewer adults, and target juveniles instead—but at sustainable quotas, based on the natural quotas we see in other predators. Such a sea change, says Reimchen, wouldn’t be difficult. “There’s all sorts of simple, technical solutions”—including using flexible hooks or lobster traps that target smaller animals specifically—“that can help us shift away from the reproductive capital,” he says. “We could do it without much difficulty.” We may be the world’s top predator, but when it comes to sustainable predation, it turns out we have a lot to learn.

Aug. 19 2015 9:06 AM

Hummingbirds Are Fierce, Deadly Gods of War

Hummingbirds seem to be composed of equal parts bumblebee and electron, and they sport coats of iridescent feathers so fetching, you’d think every day was Fat Tuesday. They’re the world’s smallest birds, weighing less than nickels do, and they just seem so, well, adorable. But the Aztecs had a rather different view of these birds.

According to legend, the earth goddess Coatlicue once picked up a bundle of hummingbird feathers that had fallen from the sky. Storing them near her bosom, she became with child. This angered Coatlicue’s other 400 children, so they conspired to kill her—but the moment they did, a fully grown, heavily armed, and mad as hell Huitzilopochtli sprang from her womb and started cutting off heads.  


Huitzilopochtli is the Aztec god of war and the sun. He is depicted either as a hummingbird itself, or as a warrior with hummingbird feathers on his helmet. When Aztec high priests cut out the hearts of enemies and slaves, it was to honor and feed the hummingbird god. (If Huitzilopochtli was happy and fed, the Aztecs would be triumphant in war and conquest.)

As a symbol of their connection to Huitzilopochtli, Aztec kings were fashioned with cloaks made entirely of hummingbird skins. Imagine the way such a garment would shimmer in the sun, especially given the way hummingbird feathers reflect and refract light to create otherworldly waves of colors. (If you’re wondering how many hummingbirds it would take to make an adult-size cloak … good question. About 8,000.)

Aztec origin myths aside, hummingbirds really are badasses. And there’s a biological reason why: Their lives depend on it.

You probably already know that hummingbirds can perform all sorts of crazy flight maneuvers, like hovering in place and flying backward and even upside down. The little dudes have no problem drinking nectar out of a revolving feeder.  

These acrobatics push the animal’s body to the absolute metabolic limit for vertebrates. Every day in the life of the hummingbird is spent between the ruin of overexertion and the reward of nectar won. To make matters worse, they have a very low capacity for storing energy, and their small body size makes it difficult to stay warm. When it’s cold at night, some species have to go into torpor, a hibernationlike state. “They basically couldn’t survive eight hours without food or fuel if they were at their regular metabolism,” says Geoff LeBaron of the National Audubon Society.

There are more than 320 species of hummingbirds from Alaska to southern Chile—they’re strictly New World birds. They range in size and diet, but you can generally estimate that a hummingbird will eat between 1½ to 3 times its own body weight in nectar each day. And that nectar is chock-full of sugar. Scientists estimate that the average hummer eats about half its body weight in sugar each day. (Yes, hummer is an accepted term for hummingbirds. Get over it.)

According to my rough math, that’d be like a 200-pound adult human drinking 1,163 cans of Coca-Cola each day. (If you’re a Pepsi person, it’d be slightly fewer—1,106 cans per day—because Pepsi is more sugary than Coke.)

Anyway, to make this constant nom-nomming possible, hummingbirds come equipped with excellent spatial and temporal memory. They not only know where the nectar sources are within a given territory but how good they are and when they’ll become available, says Paulina González-Gómez, a research associate at University of California, Davis. If you take a feeder down and see a hummingbird hovering near the spot and think it’s glaring at you, it’s not your imagination.

Males take all of this to the next level by establishing and defending territories. They’ll throw down with rival males, females, and their own reflection in a window. They’re also not above telling a bee to buzz off by giving it a quick flick of the beak or chasing a much larger bird out of their flower patch.

When hummingbirds fight each other, it usually involves chases and vocalizations meant to scare or simply harass the intruder until it goes away. Sometimes, these encounters escalate to grappling each other with their claws, though you’d need a high-speed camera to catch it. Sometimes, LeBaron says, fatal collisions can occur.

“It’s not that their aim is to kill,” he says, “but they can impale each other, and then that’s the end.”

At least one species of hummingbird, Phaethornis longirostris, actually has a beak designed to be a weapon. A study published last year by some of González-Gómez’s collaborators found that the beaks of adult males were like stilettos, longer and pointier than those of juvenile males or females—the better for stabbing other males in the throat.

“I'd say that if hummingbirds were ostrich-size birds they would be extremely dangerous,” says González-Gómez.

Interestingly, there’s a saturation point at which most aggression ceases. You can see it on display at any flower garden or aviary where there are more nectar sources than one hummingbird could reasonably defend. But the point is, he doesn’t need to. Hummingbird aggression costs a ridiculous amount of energy. If there’s a surplus of food, it’s pointless wasting energy trying to defend it.

Aggression may also play into mating success for the males. Another study by González-Gómez found that higher levels of testosterone were positively related with body condition in Anna’s hummingbirds. González-Gómez says this could mean aggression is linked to mating success, since better-defended territories lead to healthier males, which would in theory be more attractive to females. However, the relationship between testosterone and body condition was less pronounced in other species, indicating that other factors play a role.

Researchers are still determining just how all this sugar-rage fits into the birds’ life history, but it’s obvious that the male hummingbird is disproportionately confident for his size.

LeBaron says he once saw a male hummingbird harass and sort of chase a golden eagle. “Which seems a little over the top,” he laughed. A screaming-freakin’-eagle vs. a bird about the size and weight of a Dum Dums lollipop.

No wonder the Aztecs believed warriors cut down in battle would be reincarnated as hummingbirds—ounce for ounce, there’s probably no fiercer creature on Earth. And to think, you can lure these little war gods to your porch with nothing more than a red feeder and a little sugar water.

Aug. 17 2015 9:40 AM

A Peacock Must Be More Than Glorious

It’s easy to scorn the peacock. To watch him as he preens, struts, and turns unabashedly to check out his own behind is to understand exactly how he earned his reputation as nature’s most noxious narcissist.

Just ask Purdue University peacock researcher Jessica Yorzinski, who has seen him at his most undignified: performing his entire mating display for the wrong species. Yes, that's right. Before Yorzinski's eyes, the peacock has fluttered his feathers, bowed his head, and let loose his obscene squawk while charging lustily toward the object of his desire (a spectacle known as the "hoot and dash")—only to find out that he's attempting to mount a squirrel.


“I have not yet seen a successful completion to that,” Yorzinski says drily. “The squirrel gets out of there pretty quickly.”

How could nature have molded a creature so ornamental, so unwieldy, and with such costly accoutrements? In fact, that is the question that kept Charles Darwin awake at night. Initially the peacock’s train, showy and cumbersome, seemed to contradict his grand theory of natural selection—that animals succeed or fail based on their adaptive traits. “The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me sick!” Darwin once wrote to a friend.

But to dwell on the ungainliness of this troubling bird was to miss the point. Peacocks were just as subject to selective pressures as any other animal; the pressures they were responding to were just a little different. Like other lekking animals—including the sage grouse, the hummingbird, and the Mediterranean fruit fly—they had evolved to display before the females of their species in a group of other males. And boy, could peahens be choosy: In the average peacock lek, around 5 percent of the males get the majority of the mates, while nearly all the rest get zilch, according to research by Roslyn Dakin at the University of British Columbia.*

Talk about a strong incentive to please your woman!

And so Darwin, like peahens, began to recognize the use in the peacock’s uselessness. Instead of a threat to his theory, this bird became its poster child: His very unnecessariness made him the ultimate example of how selective pressures could forge dramatic changes in a species. “Often we come up with new wrinkles, but the theory (of natural selection) is so cogent in a way that we really shouldn’t be surprised that it works,” says Robert Montgomerie, an evolutionary biologist at Queen’s University. Today, researchers like Yorzinski and Montgomerie and others are building on Darwin’s insights.

For instance, it turns out it takes more than just appearance to attract a peahen. Recent research in Animal Behaviour found that peacocks rely on sound and movement as well as their looks, making infrasonic coos that human ears can't detect in order to attract the ladies. “The emerging picture is that the auditory itself may be far more important than the visual domain,” says Jim Hare, an animal behavioral scientist at University of Manitoba and lead researcher on the study. Hare has even seen peacocks in captivity whispering their sweet nothings to the empty walls of concrete bunkers—the audio equivalent of practicing their technique in front of a mirror.

To be successful, the male peacock must not be merely glorious; he must be more glorious than all of his peers. In her latest unpublished work, Yorzinski used cutting-edge eye-tracking technology to follow male peacocks’ gazes. She found that they spend a whopping 30 percent of their time assessing the other males in their lek in an effort to judge the competition. This might sound like a waste of time, but according to Yorzinski, it isn’t. “The males can get into some pretty costly fights with each other,” she says. 

Is all that huffing and puffing really necessary? Unfortunately, yes: Peahens, it turns out, are a rather rude audience. In previous eye-tracking studies, Yorzinski has found that peahens often appear not to notice the male’s rich display. Instead, their gaze wanders, or they peck nonchalantly at the ground, even as the male tilts his feathers against the sun in an arc of shimmering iridescence. To get them to notice him, he must play every trick up his sleeve. (Including deception: He has even been known to make fake mating hoots to act like he’s getting more mates than he really is.)

How can we regard this bird, nature's ultimate object, as anything other than an object of pity? His confident strutting masks a deep desperation: If his efforts are unconvincing, all is for naught. He will get no ladies, pass on no genes, and have no impact on the future of his species. He will be but a showy speck in the sands of time. As Yorzinski puts it: “The males can fight all they want, and it probably helps them get a good territory where females are passing by, but ultimately it comes down to what the female wants.” 

And yet: Who among us has not debased him- or herself in the name of love? Who has not burned with such passion that, for a moment at least, we have gone temporarily out of our head, losing all sense of  self-awareness, in our single-minded pursuit of that elusive, effusive other? Without the eyes of the other—“the single assumption which makes our existence viable: that somebody is watching,” in the words of Tom Stoppard—we too would be revealed in all our desperate acts of affection, “every gesture, every pose, vanishing into the thin, unpopulated air.”

For love, it seems, is like the peacock’s tail: blind, yet full of eyes.

*Correction, Aug. 19, 2015: This article originally misattributed a peacock mating statistic to Angela Freeman. The research was by Roslyn Dakin.

Aug. 12 2015 9:53 AM

Nature’s Most Delightfully Depraved Parasites

Somewhere in Japan, a wasp swoops onto a spider and jabs it with a stinger. The wasp’s venom paralyzes the spider for 10 to 15 minutes, during which the wasp secretes a tiny egg.

By the time the spider wakes up, it is doomed.


Soon, a larva will hatch from the egg and immediately begin siphoning juices out of the hapless spider. The larva will grow quickly, never once releasing its death grip.

To put this in perspective, imagine carrying a blood-sucking maggot on your back that grows to the size of a carnival teddy bear.

And oh, by the way, that teddy bear has a command for you. It’s just one task, but you have to do it for the rest of your life.  

Orb weaver spiders parasitized by this species of wasp, Reclinervellus nielseni, are basically turned into zombies. To add to the indignity, they are forced to embark upon an Extreme Makeover: Web Edition.

First, the spider removes the sticky spiral section of its web that it uses to catch food. Then it disassembles the struts that radiate out from the web’s center until only a few support beams remain. The zombie spidey then reinforces what’s left—its spinneret churning out layer after layer of silk like a hormonal teen etching his beloved’s name in a desk during study hall.

When the remodeling is finished, the larva sucks the last sip of suds from its host, crunches up its carcass like an empty can of beer, and tosses the spider unceremoniously into the weeds. The video below has no sound, or we’d no doubt hear the ungrateful larva belch before weaving its cocoon and hunkering down for metamorphosis.

I think it’s safe to say that we’re living in the age of peak zombie. Elijah Wood, Arnold Schwarzenegger, and even the Terminator’s son Patrick Schwarzenegger have zombie flicks coming out this year or next. Pride & Prejudice & Zombies is getting a movie, and World War Z is getting a sequel. This month, AMC is premiering a spinoff of The Walking Dead, which is itself still running.

In most of these pop culture depictions, zombies are chaotic, mindless killing machines. They don’t think, they don’t feel, they merely chase, claw, and chomp until the credits come to save us.

But nature is also full of zombies—slightly more nuanced zombies—and we’re learning more bizarre things about them all the time.

We’ve known about the zombie spiders for more than a decade, but new research just published in the Journal of Experimental Biology is the first to show that the web the larva forces the spider to build has superior tensile strength.

As to why the larva should require such a bunkerish web, the study’s lead author, Keizo Takasuka, an ecologist at Kobe University in Japan, has a few ideas.

The webs the zombified spiders create are actually very similar to those that healthy, nonpossessed spiders make just before they molt. (Molting occurs when spiders and other arthropods grow too big for their exoskeletons and have to do the fat-guy-wiggling-out-of-a-little-coat dance.)

However, a molting spider requires just 48 hours to shrug out of its skin, whereas the wasp larva needs more than 10 days to make its transformation to an adult. During that time, the wasp and its web are vulnerable to falling debris, wind, rain, and many other kinds of damage. A super-strong web gives the pupating wasp the best chance of moving on to its next stage of life. The spiders even adorn their webs with a few cottony patches of ultraviolet-reflective web so that birds and big insects can see the structure and won’t run into it.

This sort of mindhack plays out across many different species of spiders and wasps.

Tommy Leung of the University of New England—who runs an excellent blog called Parasite of the Day—says real-life zombies are more complicated than the ones we see on the screen. “It's not so much that the hosts become zombies in the classical sense of being mindless, shuffling husks, but that they are acting under the influence,” says Leung.

Put another way, it’s as if hosts come preprogrammed with certain behaviors, and the parasites have learned that it’s easier to hijack those programs rather than write a bunch of new lines of code.

For example, each autumn, Japanese yellow hornet queens—the ones that decapitate honeybees—go out in search of new nests. When they find the perfect one, say in a nice decaying log, the hornets carve out a little hole and start ordering cute prints from Etsy.

However, Leung has written about a parasitic nematode that can make these queens think it’s autumn when it’s actually spring. The queens then fly from potential nest to potential nest, stopping just long enough to let off a load of nematodes. When true autumn rolls around and nonparasitized hornets show up to start making nests, the nematodes are already sitting at the dinner table, clutching forks and knives, ready to infest any eggs she lays.

Does the parasite make its host do anything crazy? Nope, the nematode just rearranges the hornet’s day planner to better fit its own schedule. (Oh, and uses the hornet like an Uber car while sterilizing the queen in the process.)

Elsewhere in the animal kingdom, there are caterpillars who like to climb up and down trees every day. Parasitic viruses simply disable the “down” button, the better to position the caterpillars for when they turn into exploding sacs of infectious viral particles.

In another example of zombification, ants leave their colony when sick, which is thought to protect their nest-mates from infections. However, there’s a fungus that uses this script for its advantage, commandeering the ill ant’s self-sacrifice code and guiding the insect high up onto a branch. The ant’s carcass then sprouts a stalk of death spores and rains them down on all the other ants from above.

But my favorite example is that of the crab-castrating barnacle.

Now I’m aware that the barnacle, as an animal, is not high on the list of most human’s interests. (Darwin, though—he loved a good barnacle.) Most barnacles are sedentary, dully colored, and well, kind of pathetic.  

But Sacculina carcini and its ilk are not your average barnacles. As larvae, the females float around searching for a suitable host, which they then inject themselves into and eviscerate with long, probing roots. If the host crab is unlucky enough to be male, his genitals are replaced with the barnacle’s own reproductive organ.

After awhile, a free-floating male barnacle comes along and fertilizes the Master Blaster hybrid of female barnacle and castrated crab, and the parasite begins to produce thousands of larvae. It keeps these in big white sacs where the crab would normally harbor its own young.

So where does the zombie part come in? Regardless of which sex the crab was before the barnacle took up residence, it will now behave like a mother—to the parasite’s brood.

The crab wafts fresh, oxygenated water over the parasite’s developing larvae, keeps them clean, and protects them from predators. The crab stops eating and, possessing no genitals of its own, abandons any attempts at passing on its own genes.

The study of how this sort of possession works on the molecular level is, as Leung says, very much in its infancy. The wasps may be keying in on a hormone that tells the spiders its time to molt, but myriad other proteins and molecules may do the dirty work in other species. In fact, some parasites manipulate their host’s behavior simply by showing up.

Leung says he spent several years studying a fluke called Curtuteria australis, a parasite that likes to burrow into the foot of New Zealand clams. Now, one fluke in your foot is no big deal if you’re a clam, but these flukes love company.

“As the clam gets infected with more and more of the parasites, the foot becomes something less like a muscular organ and more like a bag of parasite cysts,” says Leung.

Eventually, the fluke-ridden foot becomes useless, and the clam can no longer dig itself into the sand. This makes it more likely that the clam will be found and devoured by a hungry bird, which, it just so happens, is exactly what the fluke requires to complete its life cycle.

Now, you could look at all of this and start to feel bad for the billions of hosts who have their minds warped each day, all those exploding caterpillars and hijacked hornets. But I think that’s the wrong takeaway.

Instead, I feel like we should be raising a glass to the parasites—nature's original social engineers. After all, what evolutionary trick could be more impressive than the ability to pirate another species' evolutionary tricks?

July 24 2015 3:04 PM

Black Widows’ Bizarre Mating Rituals

Pickup artists could learn a few tricks from the male black widow spider: Target single virgins. Communicate that you’re interested. Help yourself to any snacks she has lying around. And—most importantly—tear apart her home, fashion the broken pieces into a bundle, and wrap the bundle in silk secreted from your butt (sorry, your spinnerets).


Sounds sexy, doesn’t it? How could she possibly resist? But given that black widow females are famous for devouring their mates even after a good date, I have to ask: Why do the puny males dare destroy the webs of the large, carnivorous females?

July 20 2015 4:25 PM

Athens’ Zoo Animals Are at Risk of Starvation

Dolphins do not usually have to worry about financial crises. But Greece’s current economic troubles may soon have a deadly impact on the dolphins, penguins, lemurs, and other animals in Attica Park, Athens’ only zoo. Many of the zoo’s 2,200 residents require imported specialty foods to survive—yet government-imposed restrictions on cash are blocking the zoo’s ability to access foreign shipments. And without immediate relief, some of the zoo’s animals may be just weeks away from starvation.

The trouble for Attica Park arises from the Greek government’s capital controls. These rules severely limit cash withdrawals from Greek banks, as well as money transfer to foreign banks. Spooked by Greece’s economic woes, the zoo’s suppliers are demanding cash in advance. But Jean-Jacques Lesueur, Attica Park’s founder, can’t access or transfer adequate funds to pay his suppliers in France, Germany, and the Netherlands. As a result, his zoo may soon be cut off from the fish, worms, additives, and other enriched foods necessary for some animals’ diets.


When countries descend into political or economic turmoil, zoo animals often fall victim to food shortages like this one. During the 2014 Ukraine crisis, 9,500 animals at the Kiev zoo faced awful conditions and narrowly averted starvation. Dozens of lions and tigers at a Crimea zoo came close to going hungry when Ukraine cut off funds to the region following its annexation. The animals of the Baghdad Zoo were devastated during the 2003 invasion of the city, dying of starvation and thirst. (Conservationists and the United States military worked together to eventually repopulate the zoo.) Conflicts in Kuwait, Kosovo, and Afghanistan also led to the abandonment and death of thousands of zoo animals.

The fauna of Attica Park face a financial crisis, not a war. Their outlook, however, remains bleak. Even if the government relaxes its capital controls, the zoo’s attendance has plummeted as disposable income in the country runs dry. Just as ominously, Greece’s new bailout detail arrives with a massive new tax that will hit Attica Park hard. Right now, Lesueur just wants to keep his animals fed; beyond that, he has no long-term plan to keep the private zoo afloat. It seems that, in 2015, a zoo may be a luxury that Athens simply cannot afford.

July 9 2015 2:04 PM

Bumblebees Can’t Handle the Heat, Can’t Escape the Kitchen

There’s plenty to grumble about if you’re a bumblebee. When humans aren’t mooching off your free pollination services, they’re blasting you with deadly, disorienting toxins or encroaching on your ever-dwindling wildflower habitats.* Plus, you’re constantly fighting off invasions of parasitic mites that threaten to collapse your colonies. All told, you and your brethren are dying out at rapid rates.

As if that’s not enough, now bees have another thing to worry about: the rising heat. Bumblebees are facing critical declines across both Europe and North America due solely to climate change, reports a new global study published this week in Science. As temperatures rise, these humble bumblers are failing to migrate out of their homelands, which are rapidly becoming inhospitable to their survival. This is bad news for bumblebees, and it’s also terrible news for humans.


Pollination by insects—mostly bees—is necessary for 75 percent of the crops we depend on for food. As bees have declined over the past few decades, our reliance on them has become abundantly clear. United Nations Under-Secretary-General Achim Steiner put it eloquently back in 2011: "Human beings have fabricated the illusion that in the 21st century they have the technological prowess to be independent of nature. Bees underline the reality that we are more, not less dependent on nature's services in a world of close to seven billion people."

The United States has launched a multimillion dollar task force to save the country’s pollinators. The task force spotlights the domesticated honey bee, which farmers depend on for $15 billion worth of crops. Yet recent research shows that wild, native bees are actually far more effective pollinators—and these are the bees that are most vulnerable to climate change. Wild pollinators like bumblebees "are as or more important than honey bees for crop pollination,” says Claire Kremen, a conservation biologist at University of California, Berkeley, who researches pollinators and who was not involved in the new study. “Their importance has been underestimated.”

So it’s doubly unfortunate to find out that these MVPs—most valuable pollinators—are rendered helpless in the face of climate change. Researchers looked at 67 species going back 110 years, to find that bumblebees have lost up to 300 kilometers from their southern ranges across both North America and Europe. At the same time as their southern habitats are being made unlivable, these bees are failing to move to more habitable northerly ranges. Thus their habitats are being compressed from both sides: Like Luke Skywalker & co. in the Death Star’s trash compactor, they’re being slowly squeezed into nonexistence.

It’s not as if bees are the only ones facing these threats: Birds, butterflies, and other insects all have to adapt to the same changing climate. Yet many of these pollinators are doing just fine. Not to rub it in, but many species of butterflies are virtually thriving, embracing warmer temperatures and rapidly expanding north into new horizons. So why are bumblebees dragging their furry feet?

Part of the answer lies in their evolutionary history. Butterflies evolved in the tropics, making them perfectly at home in the warmth and sunshine. Bumblebees, by contrast, originated in the cool conditions of the northern Palearctic zone. In other words, their biological machinery is ill-equipped for running in warmer climes. “Imagine a car that starts running out of coolant and steam starts coming out of the hood,” said University of Ottawa biologist and lead author of the new study Jeremy Kerr, at a press conference Wednesday. That’s the bumblebee, beaten and beleaguered.

Another reason is the difficulties inherent to bee colonization. Bees are mobile little beasts, but it takes a lot to get them to settle down. Unlike butterflies, who just need a male and a female to get going, bees require a queen and a critical mass of new males to establish a colony. For this, they rely on seasonal cues: Bees forage in the spring and summer, and then produce new males and queens at summer’s end. When those seasonal cues are interrupted, delayed, or don’t happen due to climate change, bee colonies fail to take root.

Perhaps, the researchers say, bees just need a little help from their friends. After all, we caused this environmental mess, so maybe we can fix it. Humans to the rescue: Kerr says we need to seriously consider the idea of “assisted migration,” or physically moving bees northward to try to nudge them into taking root in colder climes. Such a drastic move would require serious ethical considerations and international buy-in—but the situation might just be critical enough to warrant it. “This is not just something to worry about at a vague future time,” says Kerr. “This is happening now.”

But is that really the most efficient path? UC Berkeley’s Kremen says we may need to build landscapes that would mitigate climate change for many species, not just one. “It won't just be bumblebees but many species that would need this kind of assist,” she says. In fact, that’s just what Obama’s task force has in mind: This summer it announced a plan to build an ambitious pollinator “highway”—a 1,500-mile corridor that would aid bees and butterflies in flying between Canada, the U.S., and Mexico. 

“Of course,” Kremen adds, “What we really need to do is deal with the root of the problem: our runaway consumption patterns that are causing this degree of climate change.” Until then, we’ll probably just keep bumbling about.

*Correction, July 9, 2015: This article originally misstated that bumblebees are used for their honey services. They are actually used for pollination.

June 30 2015 5:46 PM

Don’t Forget: Eating These Clams Can Cause Amnesia

Unlike the flashing blue-ringed octopus or the smelly rubbish bird, the Pacific razor clam isn’t in-your-face poisonous. This dark-shelled clam quietly dwells along beaches from California to Alaska, diligently filtering algae from the ocean. Usually, the clam’s not poisonous: Humans and wildlife both enjoy its “particularly delicious” flesh. But under certain conditions, the clam’s flesh harbors domoic acid, causing diarrhea, amnesia, and even death. The conditions that turn this savory clam toxic are becoming more widespread—and we humans are to blame.