What evolutionary pressures lead to female praying mantis consuming the males, but their headless bodies still reproduce?

Question

So the females bite the heads off the males, and later the whole body, but the male’s body finds it’s mating spot and continues to mate for hours

Attenborough describes as hormones and enzymes being responsible, and that the female derives much energy from this exchange resulting in more eggs, but why are they driven to do so?

What selection pressures would select for this? There are other insect species that don’t need to consume their partner, nor do they need the extra energy. The male being able to mate after being headless would also have been selected for? I don’t understand why this would be the case

In: Biology

Answer 1

Just as a preamble, sexual cannibalism is not observed in the vast majority of mantis species, and in those species in which it does occur, it’s more likely not to happen.

That said, it *does* happen in the wild, with a rate of around 1/3rd of all copulation involving cannibalism in some species ([cite](https://www.sciencedirect.com/science/article/abs/pii/S0003347205810176)). And it’s *not* a winning strategy. A [recent study](https://royalsocietypublishing.org/doi/10.1098/rsbl.2023.0505) found that sexual cannibalism, particular before mating, dramatically reduces genetic diversity and population levels. Reduced diversity means reduced opportunities for selection, which means more mutations will be propagated, which is even *worse* for the survival of the population.

So sexual cannibalism seems to be a *really bad* thing for species that practice it. So why do it?

It may be that it is advantageous for the offspring of the female to a degree significant enough that it’s worth sabotaging the entire species. We see similar behavior in some mammals which will kill and sometimes eat the young of their own species; it’s bad for the species/local population as a whole, but good for the offspring of one individual.

Or it might just be a behavior which has been selected for but is not maladaptive, like the extreme reluctance of pandas to mate. Not all behaviors are positive ones.

Since the genetic research I linked to above was published just a few months ago, it seems as though this is an unsolved question in biology which is being actively researched.