It's a protection racket of sorts with sex as the apparent payoff.

Researchers from The Australian National University in Canberra have found that male fiddler crabs will happily defend a female neighbor against intruders -- partly because the females will dole out sex in return.

Fiddler crabs are territorial and live in burrows and researchers say the behavior is unusual for territorial creatures. They also note that swapping sex for favors is not unheard of in the animal kingdom.

Michael Jennions helped conduct the study which is published in the journal Biology Letters. He says the results suggest that male crabs preferred to keep females nearby, largely because they will almost always mate with their male neighbors.

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