Fiddler Crabs: World's Pickiest Mates

When female fiddler crabs pick a mate, size does matter. The size of his house, that is.

Females spend big chunks of time looking for a male with a perfectly-sized burrow, which will give their offspring the best chance of survival.

"The size of the male's burrow affects the development time of his larvae," said Christine deRivera of the University of California, San Diego. "A burrow of just the right size allows larvae to hatch at the safest time, the peak outward nighttime flow of the biweekly tidal cycle."

The males attract mates by standing in front of their burrows and waving their enlarged claws at females passing by.

"The California fiddler crabs use a lateral wave that looks much like a human beckoning 'come here'," deRivera said. "It also seems to serve as a 'come hither' signal, as a male waves, standing at his burrow entrance, and interested females come over."

The females check out the burrow, and if it appears suitable, the two crabs will plug up the burrow, mate, and incubate their eggs, which will later hatch and release tiny crab larvae.

Most animal species sample just a few potential mates, but female California fiddler crabs are much pickier. In deRivera's study, females checked out male suitors and their bachelor pads an average of 23 times before making a final selection. One particularly choosy crab visited 106 male burrows, fully entering 15 of them, during her hour-long search.

--Bjorn Carey

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Credit: Catherine deRivera