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10 Animals With Cannibalistic Sex Habits

by Hannah Stephens
fact checked by Jamie Frater

Some postcoital practices are far more dangerous than an after-sex cigarette. If you belong to an arthropod species where one partner frequently devours the other, making babies may be the last thing you ever do.

Some species of spiders, slugs, and insects regularly include a spot of cannibalism in their reproductive habits. It’s usually the males that draw the short straw when it comes to getting eaten while trying to pass on their genes. So strong is the urge to reproduce that the males of some species will even willingly sacrifice themselves for the cause.

Featured image credit: National Geographic

10 Orb-Weaving Spiders

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If you’re a male orb-weaving spider, your chances of surviving your first sexual encounter are poor. In fact, you have more than an 80 percent chance of being eaten by the female.

As this means that they probably have only one shot at passing on their genes, male orb-weaving spiders are fairly picky when it comes to choosing a mate. In many other species, females do the choosing.

However, like most other animals that practice sexual cannibalism, male orb weavers are more selective than the females when it comes to picking a sexual partner. They tend to go for plump, young females in the hope that they are the most fertile.[1]

9 Redback Spiders

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Male redback spiders willingly sacrifice themselves to pass on their genes, and there’s a high chance of death at every stage of their mating process. Male redbacks don’t spin their own webs. Instead, they often hang around the edge of a female’s web and make sexual overtures toward her to see if she’s ready to breed.

If she hasn’t already eaten him by this stage by having mistaken him for prey, the male then goes to extreme lengths to maintain her attention while they get down to business. He stands on his head and allows her to access his abdomen by “somersaulting” it toward her mouth.

This gives him time to insert his first palp (reproductive structure) while she is busy injecting digestive juices into his abdomen to liquefy his insides. If he still has the strength, he may be able to insert his second palp before succumbing. It is thought that this unusual way of reproducing is only exhibited in redback spiders.[2]

That’s not the extent of the redback spider’s deadly tendencies. Although each egg sac contains around 300 eggs, the babies are so cannibalistic that very few will survive to adulthood.

8 Banana Slugs

The banana slug performs a postcoital ritual of self-cannibalism that would make any man’s eyes water. Like most types of slugs, these yellow mollusks are hermaphrodites. Although they are capable of fertilizing themselves, they usually choose to reproduce with a partner if potential mates are available. Banana slugs signal that they’re ready for copulation by releasing chemicals into their slime.[3]

Once they’ve found a mate, banana slugs get in the mood by consuming each other’s slimy secretions. When they’ve finished exchanging sperm, they gnaw off their own penises to disengage from their partner.

7 Octopuses

Photo credit: BBC

Although sexual cannibalism is less common in octopuses than some other species on this list, the males still take a big risk whenever they copulate with a female. Despite being generally antagonistic and antisocial toward each other, octopuses have a surprisingly intimate way of making babies. To fertilize the female’s eggs, the male must insert one of its arms inside her body.

Female octopuses sometimes strangle their mates by wrapping their arms around the males’ bodies and squeezing. Then the female drags the body back to her den to consume it. This is most likely to happen in species with long arms, such as the coconut octopus.

To minimize the risk of becoming dinner, many long-armed species mate from as far away as possible by reaching their arm into the female’s body from a distance and actually keeping her at arm’s length. Some males even do this from outside the female’s den.[4]

6 Anacondas

Photo credit: National Geographic

Female anacondas occasionally cannibalize their partners by strangling them. They have size on their side—the females are nearly five times as large as the males.

It seems that males prefer to mate with large females, although scientists were flummoxed as to how they could gauge the size of a female given their bad eyesight. It’s thought that the pheromones that attract males to a female contain information about her physical appearance.

It makes good sense for a female anaconda to eat her mate. Once she’s pregnant, she won’t eat again for the seven months of her gestation. So, getting a last-minute meal in beforehand is a good tactic to keep her going through a long pregnancy.[5]

5 Sagebrush Crickets

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To avoid being completely devoured by females during mating, male sagebrush crickets offer a gift of a particularly gruesome kind. While they mate, the female feasts on the male’s back wings and drinks the juices that ooze out. Only a part of the wings is eaten during copulation, so the male may be able to mate again.

However, males that have already mated aren’t usually as attractive to females because their partially eaten wings offer a less filling meal. This means that virgin males are the first choice for a female sagebrush cricket looking for a sexual partner.[6]

4 Jumping Spider

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Male jumping spiders aren’t at all picky when it comes to finding a mate. In fact, they will attempt to seduce any female they encounter with a special mating dance, even if she’s a totally different species. It’s thought that this happens because they can’t distinguish between types of spider. Scientists have even observed male jumping spiders attempting to woo dead females.

As they’re much smaller than the females they’re trying to win over, male jumping spiders are very vulnerable to being eaten by their mates. Females generally try to eat their suitors after mating, although they don’t always succeed. The male may not fare any better if he accidentally sets his sight on one of the many other species that devour males after sex.[7]

3 Black Widow

Deadly Mates: Black Widow Spider | National Geographic

A commonly believed myth says that black widow mating always ends with the female cannibalizing the male. However, many different species fall under the black widow umbrella. Of these, most do not partake in sexual cannibalism in the wild, although it has been observed in captivity.

Of the black widow species in the United States, only one exhibits cannibalistic behavior after mating. Latrodectus mactans females, often known as the southern black widow, do sometimes polish off their partners following copulation, but the vast majority survive to mate again.[8]

2 Horned Nudibranch

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Nudibranchs are part of the sea slug family. They have jelloid bodies and get their colorful hues from the prey they eat. Despite having no teeth, they are fierce predators. They feed by shooting out a proboscis-like structure to swallow their prey whole and will happily eat their own kind if necessary.[9]

Nudibranchs are hermaphrodites, and during mating, both partners usually receive sperm to fertilize their eggs. For horned nudibranchs, this can end in one animal cannibalizing the other.

1 Praying Mantis

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Of all the species that cannibalize their mates, the praying mantis is probably the best known. Females sometimes consume the head or other body parts of their partners when they copulate. However, this only happens during 13–28 percent of mating sessions and is more likely if the female is especially irritated or hungry.

However, there may be an unexpected benefit to males if their partners do feel a bit peckish during mating. A study in 2016 discovered that female Chinese mantises who ate their mates went on to lay more eggs, increasing the male’s chances of passing on his genes to more offspring.[10]

Read more weird stories about animal sex habits on 10 More Incredible Examples of Animal Sexuality and 10 Weird Animal Sex Habits.

fact checked by Jamie Frater