Baby Please Eat Me
In our eyes, we think of a nuptial gift in the form of an engagement ring or wedding ring. And although presenting your partner with a nuptial gift is commonplace in many animal species, some spiders take it one step further.
During mating the male meets his end when the female eats him. That’s right, eats him.
This grisly occurrence is called sexual cannibalism.
What’s even stranger is that the males of these spider species appear to actually initiate sexual cannibalism.
An interesting case is of our very own Australian redback spider. During sex the male does a little somersault which places his abdomen over the female’s mouthparts, practically begging the female to eat him. She does so, during the act itself.
What the hell, right?
It seems so extreme that the males would actually want to be eaten. But there may be a good reason for this.
There are thought to be two benefits that male spiders receive for sacrificing themselves. The first is that the cannibalised male gets to mate with the female for longer and fertilise more eggs than those that survive mating. The females are also more likely to reject other suitors after consuming their first mate.
Unfortunately for redback males this all depends on how hungry the female is, as she won’t eat him if she’s full… better luck next time.
So apparently, in some species, sex is worth dying for.
But why would such a gruesome occurrence evolve in the first place?
Sexual cannibalism appears to have more commonly evolved in species where there are more males than females (male biased sex ratios), and where females are much larger than males (size dimorphism).
In some species, such as dark fishing spiders, the male always sacrifices himself, in obligate male death. Though, a lot of the time males can choose between life and death. The wasp spider is a good example of this, as the male can escape before the female has a chance to eat him. However, he can only do this during his first mating, as he will always sacrifice himself during his second mating.
The question is: what strategy is most beneficial?
This question is still being disputed, as many factors seem to influence the occurrence of sexual cannibalism. On the one hand, the male can mate with the female for longer if he chooses to hang around, while on the other, he can mate again if he chooses to leave early.
Another large uncertainty is why the female would want to eat her mate in the first place.
Although hunger is an immediate factor in some species, such as the redback spider, it doesn’t seem to be a factor in other species. The evolutionary advantage for females is also not apparent, as sexual cannibalism does not appear to increase female size or reproductive ability.
What IS known is that the bigger the size difference between males and females, the more likely it is that the males will be cannibalised.
So we don’t really know for sure why sexual cannibalism evolved in spiders, although we do have an idea as to why it would be beneficial to males.
Though personally, I’d much rather stick to an engagement ring.