Something that you might have heard about is female spiders eating male spiders, but why does this happen? Most of the time, this is something that occurs during or after mating, and there are actually a variety of different answers as to why it happens.

Various different studies have taken place to find out more about spiders and their strange cannibalistic behaviours, and this is something that we are going to look at in detail in this article.

Do Female Spiders Eat Male Spiders?

Not all female spiders will eat male spiders, but many of them will. For certain species, like widow spiders, mating can easily become a life-threatening activity for male spiders. The black widow and redback females have a bit of a reputation for eating their male partner after or even during mating with them.

More often than not, the larger female will eat the smaller male during sex, which is why they are referred to as ‘widow’ spiders. Sometimes, the female will catch the male when they are in the middle of trying to escape, but most of the time, the male spider will welcome his fate, as if encouraging the female to eat him.

Why Do Male Spiders Mate if They Are Going to Get Eaten?

A male spider will still mate even though there is a risk of death because he will still be able to pass on his genes, which is his goal. Studies have even shown that redback spider mating sessions are even longer if the male allows himself to be eaten by the female. If he sacrifices himself, he can be sure that he will fill his partner with more sperm.

Something that you might not have known is that the female will keep this sperm in two storage organs, and she will then be able to control when this stored sperm will be used to fertilize her eggs. If she were to mate again, the second spider’s sperm could, in theory, replace the original sperm, but females that have eaten their first mate are more than likely going to reject a second mate. So, a male spider can almost guarantee that he will reproduce if he allows himself to be eaten.

Another reason why a male spider would be willing to give his life to the cause is that females are not as common as males. This means that many male spiders will die in search of a mate, so if the chance comes along, they are not going to waste it, no matter the cost.

What Are the Benefits of Sexual Cannibalism for Spiders?

For females, one of the biggest benefits of eating her partner is the nutritional advantage that comes from it, and the fact that she is able to get a guaranteed meal at such a vital point in her lifetime. She might even think that she is doing the world of spiders a favour by eliminating undesirable fathers.

For the males, their sacrifice could ensure that their genes will be passed on to another generation. Some species of spiders will leave their detachable palp, which is the spider equivalent of a penis, inside the female after they have mated. This process will ensure that no other male will be able to mate with her successfully, and only his sperm will be used.

Why Do Female Spiders Eat Male Spiders?

A female spider will often eat a male spider because they are typically smaller in size, which means that they make for an easy meal. The fact that males are smaller than females in some instances means that they are much more likely to become prey. So, a simple reason for this sexual cannibalism is simply that the female is hungry or that she is guaranteed an easy meal.

There are many spider species that take part in sexual cannibalism, and various studies have shown different reasons that could explain why it happens. Some of the main reasons that have been suggested are:

  • It will benefit the species
  • It eliminates sperm competition
  • It is simply survival of the fittest
  • The female was looking for a quick and easy meal
  • The male spider was deemed unworthy

Interestingly, male spiders that are smaller than the females will be eaten after or during mating around 80% of the time. Though, in other species, like the wolf spider, where the male is bigger than the female, the male is never eaten.

There have been lots of studies that have taken place to confirm this theory, and it can be applied to a variety of spider species that have been tested. It has been found that how small the male is in comparison to the female will have a big effect on the frequency of sexual cannibalism.

Are Male Spiders Attracted to Females That Have Previously Killed Their Mates?

It is thought that male spiders are attracted to females that have previously killed their sexual partners because the risk for them is much lower. Throughout the breeding season, the female spider will be approached by male spiders that are looking for a mate. Sometimes, the female will never find a mate, and other times, she could be approached by as many as 3 different spiders.

In one study in specific, a team of experts selected 100 females and gave 50 of them a wounded male to kill and eat, while the other 50 had a cricket for dinner. A few weeks later, the team gave 20 male spiders the choice between approaching the web of the cannibalistic female or a female that had not yet eaten a male. Around three quarters of the males headed towards the cannibal female spiders. So, the results found that sexual cannibalism actually makes male spiders more attracted to their female suitors.

In addition to this, the females that had previously eaten the males were more likely to produce egg cases after they had mated than those that hadn’t. Their eggs were also more likely to hatch, which goes to show that there are benefits of sexual cannibalism

You might still be wondering why the males preferred to go to the cannibalistic females than the other females, and the explanation for this is quite interesting. This is thought to be due to the fact that females will typically only eat one male, even once they have been presented with the opportunity to do so again. It is possible that the males are more confident that they will survive an encounter with a female that has already eaten a male.