Crabs caught spying on rivals' love claws

Male fiddler crabs spy on their competitors to work out when a potential female mate is around, Australian researchers have found.

Their findings are reported today in Biology Letters.

"Males will use other males as female detectors," says behavioural ecologist Richard Milner of the Australian National University in Canberra.

"They'll eavesdrop on other males' courtship displays to detect the presence of a female."

Milner carried out the research for his PhD under the supervision of Associate Professor Patricia Backwell and Professor Michael Jennions.
Long arm of love

Male fiddler crabs have a large specialised claw that they use to fight and wave around to attract mates.

"When a female approaches a group of males they'll all start waving in synchrony and they'll all start trying to attract her," says Milner.

But knowing when females are around in the first place can be tricky because females are well camouflaged.

"The males are ridiculously conspicuous but the females look very bland," says Milner.

Milner wanted to see if males would use waving by other males as a sign there was a female around and start waving before they could actually see the female.

This would enable them to detect the presence of a female earlier than they otherwise would.