Australasian Science: Australia's authority on science since 1938

Female Fiddler Crabs Seek Protection, Not Sex

New research has resolved a mystery about why female fiddler crabs visit and leave many males during mating season – the females are actually searching for a safe haven from birds and other predators rather than hunting for the perfect match.

Fiddler crabs are found in mangroves and salt marshes and on sandy or muddy beaches of West Africa, the Western Atlantic, Eastern Pacific and Indo-Pacific, and are crucial to the ecological health of mangroves, salt marshes and muddy beaches around the world. The male fiddler crabs are known for having one claw that is considerably larger than the other.

Prof Patricia Backwell of The Australian National University’s Research School of Biology Professor Backwell found that female fiddler crabs visited successive displaying males in their burrows to identify safe places to hide in the event of predator attacks. “If a bird attacks, female fiddler crabs can move quickly and directly back to the last burrow it visited,” Backwell, said. “Having this map of burrow positions is essential if they are to survive a bird attack, and this is true for females who are looking for a mate and those who are looking for a burrow.”

Co-lead researcher Dr Marianne Peso said the team conducted experiments to observe and compare the behaviour of mate- and burrow-searching females. The team noticed female fiddler crabs that were not seeking a mate visited successive males before settling in a new burrow in the same manner as mate-searching females.

“We watched displaced females move across the mudflat, testing mate preferences with male-mimicking robotic crabs, examining male reactions to the females and testing the females’ response to a simulated bird predator,” said Peso, who is now at Macquarie University’s Department of Biological Sciences.

“In all experiments, mate-searching and burrow-searching females behaved identically. They all visited courting males, they found the same robotic males attractive, males treated them in the same way as potential mates, and all the females retreated to the last burrow they visited when swooped by the plastic bird.”

The study was published in Royal Society Open Science (http://tinyurl.com/j27ygge).