“Female fiddler crabs have sex with their male neighbours in exchange for protection against wandering male intruders, say Australian researchers. A team led by Patricia Backwell of the Australian National University report their argument in the Royal Society journal Biology Letters. Both male and female fiddler crabs shelter in burrows, which they both must defend from intruders. But while males have an extremely large claw that can be used as a weapon, female crabs have just two small feeding claws. So how do female crabs defend their territory? To answer this question Backwell and colleagues built on previous work showing that under certain circumstances, males will help protect a neighbouring male from an intruder.”