|Pennsylvania grass spider. (Wikimedia Commons/D. Gordon E. Robertson/HO)
Female spiders that eat the males they reject as sex partners aren't just in it for the tasty snack.
Cannibal females have more baby spiders than their more docile counterparts, and their spiderlings are big and healthy.
Researchers from the University of Pittsburgh took female American grass spiders, and then slowly introduced males into the mix. Some of the females -- usually the hungrier, more aggressive ones -- opted to snack on the males they didn't mate with. Others were less cruel to those they rejected.
It's unclear what a spider looks for in a mate, or in a meal, as body size or shape seemed to make no difference.
But when it comes to mating, the cannibal spiders had a major advantage. They produced thicker egg sacs, out of which more hatchlings emerged.
The study's lead author, Aric Berning, told the BBC that when it comes to spiders, "cannibals get more bang for their buck."
Sexual cannibalism is common among many spider and scorpion species.