National Geographic

VOICES Voices Icon Ideas and Insight From Explorers

Menu

Male Spiders Self-Sacrifice, Lose Genitals

If you think you have relationship problems, consider the male dark fishing spider, whose partner mutilates his genitalia and then eats him after mating. 

The male willingly sacrifices himself to ensure the health of his offspring, according to a study published recently in Biology Letters. The practice is called monogyny, and it’s relatively common among arachnids, as well as bees and ants. Scientists think this sexual cannibalism may provide an evolutionary advantage, because a better-fed female is more likely to produce healthy descendants. (Related post: “Surprise! Male Spiders Eat Females, Too.”)

“It’s almost like an extreme nuptial gift,” said study leader Steven K. Schwartz, a behavioral ecologist at the University of Nebraska-Lincoln. “He is donating his body. That allows her to produce more offspring or better offspring.”

Schwartz calls sexual cannibalism “really weird”—the scientist is clearly in awe, and rightly so.

Doing the Deed

The stakes are high for these eight-legged Romeos, and there is a lot of room for mistakes. For instance, male spiders can die before mating if they prematurely trigger one of their pedipalps, two feeler-like appendages near the mouth where sperm is stored. (See “‘Castrated’ Spiders Are Better Fighters, Study Says.”)

A fishing spider with its fish prey. Photograph by Gary Meszaros, Visuals Unlimited
A fishing spider with its fish prey. Photograph by Gary Meszaros, Visuals Unlimited

“It’s a one-shot deal, and it triggers a cascade,” said Schwartz, who’s been studying the mating habits of the dark fishing spider for years, capturing wild specimens and then bringing them into the lab for tests. “There have been a few times I’ve been handling males, and their pedipalp got caught on some cotton, and they died.”

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 1.5 hours of abdomen jiggling and light caresses—will also be eaten.

“It’s like a game,” Schwartz added. “If he doesn’t behave properly, and just starts running around, the female will usually just jump.”

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. (See “Male Spiders Give ‘Back Rubs’ to Seduce Their Mates.”)

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 give the female ample opportunity to liquidize her mate, squirting out digestive enzymes onto the male for easier eating. This creates a “sloshy milkshake, and that’s what gets sucked in,” Schwartz said.

Not only does it satiate the female, it may prevent her from mating with another male and possibly birthing the rival spider’s offspring.

Genital Mutilation

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. It’s something he refers to as a “whole-body mating plug.”

“If the male dies and gets stuck in there, his whole body prevents … male number two from mating,” he added.

Male Spiders Prefer Virgins

Though they’ll mate with any female, male dark fishing spiders tend to prefer virgins. That’s because a female who mates with only one male will bear only his offspring, thus eliminating any competition.

In one experiment, Schwartz placed males into cages with strands of either virgin spider silk or silk from more experienced females. Spider silk is similar to the kind of message dogs leave when they urinate on fire hydrants: It tells other spiders a whole host of information, like what the female has eaten for dinner and whether they’ve had sex. (Also see “Tarantulas Shoot Silk From Feet, Spider-Man Style.”)

Schwartz found that male spiders who happened across virgin spider silk spent significantly more time searching for a female to mate with than when they came into contact with silk from a spider who’d already copulated.

Mysterious Sperm

Spider sperm is mysterious: No one really knows what happens to these microscopic babymakers after they’re deposited within the female. Because the sperm has to live in the pedipalps outside the body, it’s stored in tiny capsules. (Watch a video of the world’s largest spider.)

“Once [the sperm] is in the female, we don’t know how it gets uncapsulated and … free swimming,” Schwartz said. “We also don’t know how many sperm [cells] are in one capsule.”

Luckily, “I have testes and pedipalps in tubes in the freezer,” he added. We didn’t ask if it’s next to the veggie burgers.

Comments

  1. Richard
    June 19, 1:44 pm

    Diane Johnson, why is this article “superbly satisfying”? That’s a pretty gushy response to a story about spiders. More importantly, why does your reaction disturb *me*?

    I think we humans — researchers, author and readers — all have the capacity to anthropomorphize when observing the behavior of another animal species, and that’s probably how we can best relate. It adds an emotional element to an otherwise solely-intellectual story. I suspect it’s your emotion (conveyed in the phrase “superbly satisfying!”) that I’m sensing and reacting to.

    When allowing ourselves to place human traits, values and morals on non-human organisms, stories like this one can come across (at least to a reasonably sensitive *guy* like myself) as horrific, malicious, intentional, etc — worthy of a punishment to match the crime! Though I try to separate any emotional reaction from the pure factual content, I acknowledge both. But the behavior reported here is *not* intentional (involving thought), nor malicious, nor a crime. There’s no male-female emotional angst, no misunderstanding, no revenge, no hard feelings. :-)

    Maybe you have your own set of anthropomorphically-triggered reactions. I suppose that’s what I find unsettling — that you could, in that case, derive satisfaction from “violence” against the male in the story. In other words, your inordinate fervor makes me wonder if you’re one of those sadistic male haters such as I’ve met who — while complaining about their indifference to your feelings — derive pleasure from causing men pain. If so, perhaps my sensitivity will satisfy you as well.

    As for the story (which I’m just now seeing a year later), yeah, it’s endlessly fascinating to see the variety of mechanisms that life and evolution have come up with for perpetuating the “selfish gene”! Remarkable.

  2. Eirene
    August 3, 2013, 2:07 am

    NOPE NOPE NOPE TOO MANY LEGS FOR ME THANK YOU but at least the males died happy :)

  3. Diane Johnson
    United Kingdom
    June 24, 2013, 2:54 am

    Superbly satisfying! Thanks

  4. Jamie
    United States
    June 23, 2013, 9:58 pm

    I’ll bet dinner and a movie sounds a lot better now, huh?

  5. Germanie Harris
    United States
    June 23, 2013, 5:19 pm

    Im so afraid of spiders

  6. David Meyer
    St.Louis
    June 22, 2013, 4:47 pm

    I think you mean he Snackrifices himself

  7. Franco
    USA
    June 22, 2013, 2:19 pm

    I’m speechless! “Males who don’t follow proper foreplay protocol—about 1.5 hours of abdomen jiggling and light caresses—will also be eaten.”

  8. Bala
    Katsina,Nigeria
    June 22, 2013, 7:07 am

    Very revealing and facinating.Indeed one life is worth giving for other lives to come into existence.

  9. Emily
    Philippines
    June 22, 2013, 3:20 am

    foreplay protocol—about 1.5 hours!…whew!

  10. anubhav
    india
    June 21, 2013, 9:57 pm

    indeed an incrdible n interestin infomormative effort by NG thnx..

  11. Shanthi
    Netherlands
    June 21, 2013, 12:03 pm

    Interesting article. I wonder if the male spider is aware that mating can lead to death?

  12. david nash
    England
    June 21, 2013, 7:59 am

    Interesting, I think its funny that perhaps the males “never found out” what happens when they mate. And also very funny about how they can fail.

    Perhaps its a form of reincarnation (for arachnids).

  13. Taju Shuaib
    Ethiopia
    June 21, 2013, 12:56 am

    It is really amazing what spider’s mate looks like!THANKs for the information

  14. Rob
    United States
    June 21, 2013, 12:55 am

    When mentioning bees, I assume that this is a reference to a very narrow group of the honey bees. The fact is that males of most bee species (of which there are roughly 20,000) are not threatened by cannibalism in any way, nor are they likely to die just after mating. Male bees will not only attempt multiple matings, but many will successfully complete several matings. Females of many species, on the other hand, are believed to become unreceptive to other males after a single mating. The reproductive biology and behavioral ecology of the vast majority of bee species is quite poorly known. To generalize and say that this is common amongst bees is simply incorrect.

  15. Carlos Bravo G V
    Mexico D f
    June 21, 2013, 12:49 am

    As always, Incredible and interesting! Thank You.
    Y follow your magazine, since y was 6 years old.

  16. Carlos Bravo G V
    Mexico D F
    June 21, 2013, 12:46 am

    As always Incredible and Interesting! Thank You.