The causes of cannibalism in nature

There are some magical phenomena in nature, such as individual female animals eating male animals after mating. This phenomenon is called "sexual cannibalism". Which animals can cannibalize their own kind? What strategies do males use to avoid being eaten?

The dangers of applauding love

Cannibalism, to put it simply, is the phenomenon of killing and eating conspecifics before, after, or during mating. This behavior is relatively common in arachnids such as black widow spiders, and also exists in insects, gastropods, and copepods. Common examples include robber spiders, blue-ringed octopuses, etc. A common sexual cannibalism is for female animals to eat males. Of course, there are also a few cases where females are eaten.

When it comes to cannibalism, the animal that comes to most people’s minds is probably the praying mantis. In "Black Cat Sheriff", the female mantis will eat her "husband" on the "wedding night". During the mating process, the high concentration of pheromones secreted by the hungry female paralyzes the male. Then, the female mantis will bite off the male's head in one bite, acting quickly and mercilessly with her mouth, as if the male is just a dish to her. No different than other foods.

If you sacrifice your life for mating, is it a worthy death or an unjust death?

In addition to mantises, black widows are also a typical example of cannibalism: spiders are typical creatures that cannibalize their own species, and the most famous among them is the "Black Widow".

If you sacrifice your life for mating, is it a worthy death or an unjust death?

The black widow is named after the female of this spider eats the male during mating. The scientific name of this kind of spider is the Red-spotted Crow Spider. It belongs to the Lycosidae family and the genus Crow. Its body is generally black. The size of the male is generally between 2-8 cm. It is a tall and strong guy in the spider world. The female has a red belly. The hourglass-shaped pattern, this bright red pattern is their unique logo!

Like other spiders, the black widow also hunts by "waiting". After the prey falls into the trap, the black widow will quickly attack, wrap the prey tightly with tough spider silk, and pierce the prey with its teeth. They inject venom into their prey, and after the prey stops struggling, they inject digestive enzymes into their prey and feast.

The venom of the black widow contains neurotoxins, which are extremely toxic. A few hours after a person is bitten, the pain intensifies and the wound hardens, accompanied by chills, fever, vomiting and severe abdominal pain. It can also promote the release of the neurotransmitter acetylcholine. , causing muscle contraction. Severe bites can be life-threatening.

The black widow has a very strong reproductive capacity. The female will slowly eat the male during the mating process. After mating is completed, the semen will be stored. When environmental conditions are good, they lay eggs once every 25-30 days. The eggs are wrapped in a spherical sac. They hatch in about 12-14 days and live together. During this period, if there is a lack of food, these little spiders will Eat each other.

In addition to spiders, scorpions also eat their own kind. In most scorpion species, female scorpions eat males during mating. According to statistics, more than half of desert scorpions prey on the same species.

The vast majority of sexual cannibalism involves females eating males. Of course, researchers have also discovered the phenomenon of males eating females. Male individuals of a small ant spider called Micaria sociabilis can devour females. The phenomenon of males devouring female mates has also been observed in another spider, Allocosa brasiliensis, and in some crustaceans.

Why does sexual cannibalism occur?

Richard Dawkins popularized the idea in his 1976 book The Selfish Gene that the sole purpose of biological life forms is to pass on their DNA to the next generation.

From this perspective, our bodies may be nothing more than containers containing genetic information. Once these genes are passed on to the next generation, there is no need for the body to exist.

This idea applies to many animals that reproduce only once in their lives, with males of salmon, the broad-footed marsupial shrew, and others dying after reproducing, and some males, such as male brown widow spiders, sacrificing themselves to female spiders.

An even more surprising scene is that the male redback spider somersaults directly into the mouth of the female spider after mating. Moreover, scientists have found that males who sacrifice themselves will have more offspring.

Different from the above view, some scientists believe that sexual cannibalism in many cases stems from basic needs. Pregnant women need a large amount of food to provide energy. When food is scarce, males provide the nearest source of protein.

Of course, not all males are so altruistic, and in many species, females behave in a predatory way. One theory is that sexual cannibalism is a "maladaptive side effect" of female aggression. Larger, more aggressive females tend to have greater hunting abilities and a higher chance of survival and reproduction, and males may be no different than food to them.

In addition, some scholars have suggested that sexual cannibalism is the reason why females become picky. Females will be pursued by many males during courtship, and they will select and kill the males they do not like. Studies have found that unattractive male tarantulas are more likely to be eaten.

A male who doesn’t want to be eaten

Are all males willing to be killed? no!

If the male praying mantis does not want to be eaten, he will take a very smart protective measure, that is, not to approach the female actively, and wait until the female catches other prey and has a feast before going forward to mate with it. The female mantis in the abdominal state will most likely not eat its mate.

In order to avoid being eaten, some male spiders will try their best to prevent the female from opening her mouth when mating. Some smarter ones, such as robber spiders, will bring a meal prepared long ago to satisfy the female spider's appetite, thus reducing the risk of being eaten.

Scorpions are even more ruthless. Many male scorpions will stun female scorpions before or during mating, so that they cannot bite them. He really tried his best to survive!

There are also some males who are quite scheming, such as the striped golden spider. They choose the opposite sex who is molting to mate, so that their survival rate after mating will be greatly improved.

Sexual cannibalism is a behavior that emerged during the process of natural selection. No matter what factors led to the emergence of this behavior, its existence has its reasons.

References:

[1]Saury, Shasha. Black widow spider[J]. Global Human Geography, 2015.

[2] Nathaniel  Scharping. Sexual Cannibalism: Why Females Sometimes Eat Their Mates After Sex, PLANET EARTH, 2021.

[3] Ren Tian. Male spiders can also eat female mating partners[J]. Science Grand View Garden, 2013(11):1.

[4] Ye Xiaohe. Be romantic once and lose your life[J]. Environment, 2009, 000(009):76-77.

Review expert: Ran Hao, a well-known popular science writer.

animal tags： magical phenomenon mantis mating black widow scorpion reproduction nature behavior