Bondage, Cannibalism, and Castration—Spiders' Wild Sex Lives
As love fills the air this Valentine’s Day, National Geographic takes a look at the animal kingdom’s most inventive sweethearts.
Ah, love: It can make you dance, inspire you to massage a special someone’s back—or, if you’re a spider, compel you to castrate, liquefy, and cannibalize your sexual partner.
Over millions of years, sexual selection—the high-stakes competition within a species to mate—has molded spiders into the animal kingdom’s freakiest, most inventive lovers.
“That’s why I love studying spiders,” said ecologist Eileen Hebets of the University of Nebraska-Lincoln, in a previous interview. “You often see these extreme behaviors.” (See “Wild Romance: Weird Animal Courtship and Mating Rituals.”)
So as love fills the air this Valentine’s Day, National Geographic wanted to look back through the spider’s amorous repertoire—while acknowledging that the behaviors below are just the tip of spiders’ sexual iceberg.
“There are more than 45,000 different spider species worldwide,” University of Toronto arachnologist Catherine Scott said in 2016. “And mating behavior in most of them has never been studied.”
Spiders generally don’t carry hankies. So when the males of Jotus remus—a species of Australian jumping spider—wants to get a lady’s attention, he waves the next best thing: his paddles.
The male of Jotus remus, which is about the size of an apple seed, boasts an unusual heart-shaped structure on both of his third legs. In a bizarre ritual, an amorous male hides on the underside of a leaf and thrusts the paddle high enough for a female on the other side of the leaf to see it.
Sometimes females lunge at his paddles, forcing his retreat. But unmated females stop moving when they see the paddles. When a male is assured that his ladylove is totally still, he skitters to her side of the leaf and mates with her in a matter of seconds.
“He is trying to find a female that does not attack his legs,” said Jürgen Otto, a mite expert and amateur spider scholar who discovered the behavior, in a previous interview.
The researchers know of no other jumping spider that conducts such a peekaboo courtship—nor of one that has built-in paddles on its legs.
Independent spider expert David Hill, who co-wrote the study describing the paddle-waving behavior, said that he had scrutinized a lot of spiders, but this one “is the most amazing one I’ve seen,” he says. “It’s quite a remarkable creature.”
Earning stage names like Skeletorus and Sparklemuffin, male peacock spiders perform a colorful song and dance nearly unrivaled in the animal kingdom.
Peacock spiders’ recently discovered courtship displays are among the gaudiest and most complex ever discovered, a fact made all the more surprising by their size. The little audiovisual spectacle measures less than a quarter of an inch long.
When a male peacock spider thinks he has spotted a female, “the world pretty much disappears,” Michael Kasumovic, of Australia’s University of New South Wales, said in 2015. The spider then begins a series of dances—including moves scientists have dubbed the “rumble-rump” and “grind-rev”—that send literal good vibrations through the ground toward the female.
Once he has piqued her interest, the male unfolds a brilliantly colored abdominal flap and then struts back and forth, all the while frantically waving specially colored, lengthy legs.
But recent research shows that females don’t automatically swoon to the males’ advances. Instead, females turn toward or away from males during their initial vibrations, based on the female’s interest. Some females aggressively rebuff males with quick shakes of their abdomens—or worse. “If females don’t like a male, they’ll eat them,” said Kasumovic.
When a male golden orb-weaver spider Nephila pilipes wants to get busy, he gives his mate a "back rub.”
As with many spider species, N. pilipes females are up to 10 times larger than the males, so from the male’s perspective, mating is always a risky proposition. An unlucky suitor might get interrupted in his carnal embrace when a female kicks him off and eats him.
But N. pilipes has come up with a novel solution. The male's pedipalps fit perfectly into the female's two genital openings, and he can leave them behind to "plug" the openings. But a male needs to mate several times in succession to plug both openings and guarantee the female—which can have multiple partners—will have his babies.
To make his mate more receptive in between bouts, a male N. pilipes will spread silk over her dorsum, or back, in massage-like motions known as mate binding.
N. pilipes is the only orb-weaving spider known to perform mate binding, said Matjaz Kuntner, a biologist with the Slovenian Academy of Sciences and Arts, in a previous interview. However, some spiders from other genera have been known to use the same tactic.
Interestingly, a 2011 study found that the silk itself is incidental—the female spiders are probably responding to simply being touched by their suitors.
Tying Up Lovers to Avoid Getting Eaten
Talk about ties that bind: Some male spiders tie up their partners with silken cords before and during sex.
Males across at least 30 different spider species are already known to wrap some of the female’s front legs in silk before sex, temporarily crippling her. Some species, such as the nursery web spider (Pisaurina mira), can even spin the silken cords in mid-air.
Such bonds—known as “bridal veils”—allow males to extend their mating time, letting them pass along extra sperm. The males’ kink is also a matter of self-preservation. Female spiders are often larger and more aggressive than their partners, and often try to eat males before they have a chance to mate.
That's another reason restraints come in handy: If the female is immobilized, males can slip away without getting eaten. They may also do more than just restrict. In a 2016 interview, Scott pointed out that males may add cocktails of pheromones to the silk threads, which could make a female more interested in the male.
Spiders also know a thing or two about tough love: Some male spiders lop off parts of females' genitalia to prevent her from mating again.
For at least two spider species—and potentially up to 80—males remove the females’ scapus, a bicycle seat-shaped handle that sits above their genitalia.
A male delivers its sperm via pedipalps, a pair of leg-like appendages near its mouth. But as the male dismounts, the pedipalp grasps and twists the scapus, snipping it off as if with scissors.
Without this crucial handle, other males can’t grasp the female at all, preventing her from having another sexual partner.
It’s a twist on the typical arachnid battle of the sexes. Many female spiders have sex with multiple males but fertilize their eggs with only one suitor’s sperm. This competition has prompted some species’ males to take drastic action, such as castrating themselves to plug the females’ reproductive tract.
In this case, however, “males have found a very clever means to prevent females from remating without mutilating themselves,” said Gabriele Uhl, the University of Greifswald biologist who first documented the behavior, in a 2016 interview.
If you think you have relationship problems, consider the male dark fishing spider, whose partner mutilates his genitalia and then eats him after mating.
Scientists think the male’s self-sacrifice may provide an evolutionary advantage, because a better-fed female is more likely to produce healthy descendants.
The deadly finale comes after a courtship fraught with difficulty. For instance, if male spiders prematurely ejaculate—accidentally triggering one of their pedipalps—they run the risk of dying then and there.
If the spiders manage to make it to a female with sperm intact, there’s still the chance that she’ll devour him before they get the chance to mate. Males who don’t follow proper foreplay protocol—about 90 minutes of abdomen jiggling and light caresses—will also be eaten.
If he manages to successfully approach the female, the male will insert one of his pedipalps into the female, release his sperm and then—die.
While the male’s heart is technically still beating—which it will continue to do for up to two hours—he lies immobile and helpless. This gives the female ample opportunity to liquidize her mate, squirting out digestive enzymes onto the male for easier eating.
Not only does the spider-slushie satiate the female, it may prevent her from mating with another male and possibly birthing the rival spider’s offspring.
“It’s almost like an extreme nuptial gift,” said Steven Schwartz, a Gonzaga University ecologist who has studied the self-sacrifice, in a previous interview. “He is donating his body. That allows her to produce more offspring or better offspring.”
Sometimes, males take extra, gruesome precautions to ensure their fatherhood. During copulation, the male spider can also lose parts of his genitalia. When the bulb carrying a male spider’s sperm expands, it often gets broken off inside the female. This creates a plug that prevents the female from mating again, and ensures that the male’s sperm will fertilize as many eggs as possible.
Sometimes, Schwartz says, the bulb gets stuck inside the female with the male still attached, who eventually dies. It’s something he refers to as a “whole-body mating plug.”
Mollie Bloudoff-Indelicato, Rachel Kaufman, Wajeeha Malik, and Traci Watson contributed reporting.