Some animals kill each other after sex because their distinction between hungry and flirty is blurred

Mood is everything.
Mood is everything.
Image: Reuters/Tobias Schwarz
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Sorry, cephalopod enthusiasts. For a second year in a row, there will be no Octo-Sex event at the Seattle Aquarium.

In honor of past years’ Valentine’s Day, the aquarium has organized a viewing party as they introduce two octopuses that will hopefully mate. This year, the event was cancelled because the female, a giant pacific octopus named Raspberry, started laying eggs the day before (Feb. 13)—instead she’ll be released to the wild to raise them. And the year before, it was called off because aquarium officials were worried that the male—twice the size of the female—would eat his date.

It’s not often that copulating octopuses eat one another—but it’s not uncommon either. “There just isn’t any way to measure how frequently it happens,” says David Scheel, a ecologist who studies octopuses at Alaska Pacific University. There are over 300 species of octopuses, and most are hard to study because they reclusively lurk in the depths of the ocean. Of these, a handful—including the giant pacific octopus—have been known to brutally murder and eat each other after sex. In 2014, researchers described (paywall) an instance in which a female octopus had sex with a male for 15 minutes, and then effectively strangled him with three of her tentacles by blocking his gills.

But octopuses aren’t the only ones who kill their sex partners. Female praying mantises often kill their mates, especially if they’re hungry, and within certain species of spiders, the males will actually offer themselves as a meal for their newly-impregnated partners.

Despite the ferocity of mating in the animal kingdom, romance is not dead: sexual cannibalism can be something of a gift from the male to the female in many cases. Female wolf spiders and tarantulas, who often eat males pre-intercourse, produce 30% more eggs than those who don’t when they finally get around to mating. And in the mantis’ case, the death of one male often means the survival of the reproducing female.

“It’s probably not the male’s preferred outcome,” Scheel says. “But if you think about it…contributing his calories to his offspring doesn’t do any harm [to the species].”

Also, animals don’t really think of sex as an act of intimacy the way humans do. We tend to think of mating and eating as completely separate acts, Scheel says. “But octopuses are predators, and they’re not opposed to eating each other in non-mating contexts.” Even if that non-mating context is minutes after the mating context.

This is especially true if there’s a major size difference between the two animals. In the case of an octopus, if a large male meets a small female, he may be thinking “meal” instead of “mate.” Or, even after mating, octopuses could decide that next on their to-do list is to find a meal; the closest prey may happen to be the animal they just reproduced with.

Octopus couples don’t eat each other all the time. Scheel has seen several instances of octopuses fighting after sex, but not to the death. And in some cases, a female pacific striped octopus will even live out the rest of her life with her male mate, mating and eating together “beak-to-beak and sucker-to-sucker,” according to Science magazine.