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.”)
“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.
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.
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.