Question: why do female black widows eat the the male after mating?

Ed Morrison answered on 18 Jun 2011:

Once the female has mated, she has all the sperm she needs to fertilise all her eggs and make lots of babies. By eating her mate, she gains energy for herself and her babies. The real question is why does the male allow himself to be eaten.

It may be that the male is unlikely to find another mate, so he is happy to sacrifice himself so his babies have a better chance of survival. This is what biologists call the Selfish Gene approach to animals behaviour. Even though the male’s genes in his body die, his genes in his children will survive. Of course, the spider doesn’t know this consciously, it all happens by instnct.

Or maybe they have a big argument after mating and she gets angry!