Sexual Cannibalism: Why Do Some Animals Eat Each Other After Mating?

The animal kingdom is filled with fascinating things but it also contains some darker aspects, like sexual cannibalism. Many animals often eat their partner after mating, something which still perplexes scientists. Below is more behind what sexual cannibalism is and some of the animals that do it.

What is Sexual Cannibalism?

Sexual cannibalism is when the female kills her mate after intercourse. How the female kills the male will depend on the species, but most will usually eat the male after he dies.

What is the Purpose of Sexual Cannibalism?

While it’s not quite known what the purpose of sexual cannibalism is, there are a few ideas as to why it happens.

Adaptive Foraging

Adaptive foraging revolves around food. If the animal is unable to find food when it wants or needs food immediately based on certain behavior, they could turn to sexual cannibalism. Adaptive foraging doesn’t happen instantly, rather the animal has had to face drastic changes in their normal lifestyle to survive causing them to do this.

Aggressive Spillover

Aggressive spillover is when one of the animals aggressively seeks food. Unlike adaptive foraging, aggressive spillover is believed to occur because the females are genetically inclined to be hostile toward prey and males.

Mistaken Identity Hypothesis

The Mistaken Identity Hypothesis is when the animal can’t differentiate between members of the opposite sex or if they are part of their species. This is often thought to be the reason behind sexual cannibalism with insects, particularly praying mantises.

What Animals Kill Each Other After Mating?

You might be surprised to learn that numerous animals kill their partner after mating. Below are a few of them.

Praying Mantises

The female praying mantis is notorious for killing her mate after intercourse. In fact, while mating she will rip the head off of the male and later eat his body.

While it’s still strange to researchers as to why this is done, many believe that this could be beneficial to the number of eggs a female praying mantis lays. This is because after eating his body the female receives nutrients from it which can help her to conceive and lay more eggs.

Octopuses

During copulation, female octopuses will sometimes wrap their arms around the male, strangle him, and then carry his body to an area where she will then eat him.

One theory as to why female octopuses do so is because they feel vulnerable to predators during mating. Unlike other animals who tend to only take a few minutes when mating, it can take octopuses up to an hour to do so. Because of this, it can make them an easy target for predators, something which the female might try to prevent by doing sexual cannibalism.

While most males don’t survive after mating, a few do. This is because they either swim away quickly or mate from a distance with their mating arm (known officially as the hectocotylus) to escape the grip of the female later.

Black Widow Spiders

Black widow spiders are some of the most venomous spiders to exist. They not only pose a threat to humans, but to members of their own species as well. All male black widow spiders are at the mercy of females after mating. In fact, this act is why they are called “widows”.

However, unlike many other species that do sexual cannibalism, not all black widow spiders will eat the male after mating. Some males can smell special pheromones in the female’s silk which allows them to determine whether or not the female might eat them. In addition to this, males can tell when a female is well-fed. If she is, the female spider is less likely to eat the male and he will be safe to leave after mating.

Besides sexual cannibalism, some female black widow spiders will eat undesirable male suitors as a way to prevent them from mating with her. Why a female black widow spider does this is still unknown but some research has shown that it could be based on the female’s personality. If she is aggressive she is more likely to be hostile toward males regardless if they mate with her or not.

Dark Fishing Spiders

Dark fishing spiders will mate and then the female spider will eat the male. However, this seems to benefit the male because it will help the female to produce a larger amount of his offspring. The male spider will still be attached to the female after dying allowing her to easily consume him. By eating her mate, a female dark fishing spider can produce even more eggs than if she didn’t.

Unlike other species in which the female kills her mate, male dark fishing spiders will automatically die after mating. It remains a mystery as to why the male does, but many scientists believe their body just gives out after mating. Some also think that the spiders might suffer from pedipalp expansion (something which causes the appendages on their head to greatly enlarge) during intercourse because the sperm must travel through them.

Green Anacondas

Green anacondas are yet another species that use sexual cannibalism during mating. Because females are much larger than males they will devour them after copulation. Some believe this is because the males can give a female anaconda the necessary nutrients during her pregnancy, a condition that can sometimes make it difficult for her to move around and find enough food.

As with other species that practice sexual cannibalism, female green anacondas often produce larger and healthier offspring after eating the male. In fact, studies have shown that this act can sometimes improve the immune system of the snakelets.

Sexual cannibalism is done by many different animals and insects after mating. While it’s not truly known why some species do so, there are a few guesses, such as the male body providing nourishment to the pregnant female or the female mistaking the male for prey. To many, sexual cannibalism might sound horrifying, but for many species it’s one of their only ways to ensure survival.