This Freaky Spider Bites Off Its Genitals After Sex

We tend to think we’ve seen the extremes of courtship in nature—from the flamboyant dances of birds-of-paradise to the brutal battles of elephant seals.

But the male coin spider takes things to an entirely different level.

In a post-mating ritual that is both horrifying and weirdly romantic, this Southeast Asian arachnid chews off its own genitals—not as an act of defeat, but as a strategy for reproductive success.

Here’s the wild part: this self-inflicted mutilation actually gives the male spider an edge in the ruthless game of evolution.

According to a study published in Behavioral Ecology and Sociobiology, males that removed their reproductive organs became leaner, more agile, and dramatically better at fending off rivals.

In short, they traded their future for a better chance at guarding the female and ensuring their genes get passed on.

It’s nature’s version of the ultimate mic drop: mate once, then go full eunuch—and win.

The Coin Spider’s Deadly Dilemma

The male Herennia multipuncta, better known as the Southeast Asian coin spider, starts his romantic journey with the odds stacked firmly against him.

He’s about a quarter of the size of the female, who is not only larger and stronger but also notoriously cannibalistic.

Approaching her is like walking into a lion’s den with a box of chocolates and hoping for the best.

If he does manage to mate, the next hurdle is equally daunting: he has to guard her from other males, who, if successful, could fertilize the same batch of eggs.

In the spider world, multiple paternity is common, which means a male’s evolutionary legacy is never truly secure unless he sticks around to defend his claim.

But sticking around comes with a problem: those palps, the male reproductive organs, are bulky.

In mature males, they can account for as much as 10% of their body weight. And worse, they’re only good for one use.

Once the sperm is delivered, they’re essentially dead weight—useless baggage in the high-stakes world of spider combat.

So the male coin spider gets rid of them.

Not in a tidy surgical way, mind you—he bites them off himself. Sometimes one, sometimes both.

And then, surprisingly, he carries on with life.

A Counterintuitive Strategy That Works

At first glance, this seems like evolutionary madness.

Why would a species evolve to destroy its own ability to reproduce?

But here’s where things get interesting—and where conventional wisdom starts to break down.

For a long time, scientists assumed this kind of self-emasculation was either a freakish anomaly or served no real function.

But ecologist Matjaž Kuntner and his team at the Slovenian Academy of Sciences and Arts decided to take a closer look.

They set up 60 controlled mating trials using coin spiders collected from the wild.

The females were all well-fed virgins, which minimized the chance of pre- or post-coital cannibalism—yes, that’s a real concern.

Out of those 60 trials, 32 resulted in successful copulation.

Of those, 9 males removed one palp, and 23 went full eunuch, biting off both. Interestingly, the act of mating didn’t destroy the palps.

Instead, the males would finish the job within 24 hours of copulation, chewing off whatever remained.

This is where the researchers made their big discovery.

Castration Makes You Stronger?

Here’s the twist that flips everything we thought we knew about reproduction: losing their genitals made the spiders better fighters.

Compared to virgin males who hadn’t mated or mutilated themselves, the eunuch males were significantly more aggressive.

They launched faster attacks, held their ground longer, and stayed closer to the females they’d mated with, effectively guarding them from rivals.

They also seemed to have more stamina and endurance, likely due to their reduced body weight.

As grotesque as it sounds, this adaptation gives these spiders a tangible edge in a highly competitive mating environment.

In fact, this may be one of the most extreme examples of sexual selection driving bodily change—where an animal’s ability to reproduce is directly tied not to how well it mates, but how well it can protect its mate afterward.

“Mating itself didn’t result in emasculation; that left the palps merely disfigured.

But within 24 hours of hooking up, the male always finished the job and chewed off what was left,” reported Sarah Zielinski of Science News.

The Science Behind the Strategy

To understand why this might evolve, you have to look at what biologists call sperm competition.

In species where females can mate with multiple partners, the sperm from different males is essentially in a race to fertilize the eggs.

The more mates a female has, the more intense that competition becomes.

In this context, guarding behavior becomes crucial.

If a male can stick close to the female post-mating and fend off rivals, he stands a much better chance of becoming the father of her offspring.

And if shedding 10% of your body weight helps you win those fights, it’s a worthy sacrifice in evolutionary terms.

In fact, this kind of strategy is not unique to coin spiders.

Other species of spiders and even some insects also display similar forms of post-mating self-harm, though the function has often remained mysterious—until now.

“Biting off the genitals has long been considered a peculiar evolutionary phenomenon with unknown function,” the authors noted.

But their findings suggest it’s not just bizarre—it’s strategic.

The Role of Sexual Cannibalism

We can’t talk about spider sex without addressing the giant, eight-legged elephant in the room: sexual cannibalism.

Female coin spiders, like many of their arachnid cousins, are known to kill and consume their mates—sometimes during, sometimes after, and occasionally even before mating. It’s a gruesome fate, but it’s not senseless.

From an evolutionary perspective, the female gains a nutritional boost that may help support her eggs.

Male spiders, therefore, face an existential crisis.

They may only get one shot at reproduction.

If they survive mating, guarding the female becomes even more critical—and that’s where the eunuch advantage kicks in.

This dynamic creates a powerful incentive for males to invest everything they have—literally—into one single reproductive event.

They’re not trying to play the long game. They’re betting it all on one hand, and then burning the bridge behind them.

How Far Will Nature Go?

The coin spider’s reproductive behavior forces us to rethink what we consider “normal” in the animal kingdom.

While most species rely on elaborate displays, territory, or brute strength to win mates, this spider plays by an entirely different rulebook: use it once, lose it forever—and become a better fighter for it.

And while it sounds extreme, it’s also eerily efficient.

In a world where sexual selection drives some of the most bizarre behaviors—from genital detachment in octopuses to traumatic insemination in bedbugs—the coin spider might just take the crown for most metal reproductive strategy of all time.