Why do black widow spiders kill their males after mating?
It is often said that the male (usually significantly smaller than the female, down to 1% of her size for Tidarren sisyphoides), is likely to be killed by the female after the coupling, or sometimes before intercourse has occurred. This supposed propensity is what gave the Black Widow Spider, Latrodectus mactans its name. However, the three species of North American black widows do not seem usually to kill the male (although they may) and males can sometimes live in the web of a female for a while without being harmed. The male Australian Redback Latrodectus hasselti is killed ritually by the females after it inserts its second palpus in the female genital opening; in over 60% of cases the female then eats the male. One theory is that once the male has mated, if he is unlikely to mate again then further extension of his life serves no evolutionary purpose, while the sacrifice of the male may help increase egg production through increased nutrition for the female. Having more offspring
