In the world of fiddler crabs, the best form of protection is, apparently, prostitution, according to an Australian study.

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

"The fact that the neighbour comes over and helps to defend another territorial individual is pretty unusual," said Michael Jennions, who helped conduct the study, the results of which were published in the journal Biology Letters.