Full moon super-crab: claw strength and the lunar cycle

When the moon is full, male sand fiddler crabs have more incentive to court females, and, it seems, more claw-snapping power.

The lunar cycle brings strong tidal fluxes. Female sand fiddler crabs (Uca pugilator) target these periods of new and full moons to release their eggs and let the tides sweep their larvae to deeper waters.

It is also during these times that the male fiddler crabs develop something of a lunar super power – their showy claw-snapping dances are essential to court and capture the interest of females on the prowl, so the males have to be at their best at just the right part of the cycle.

A recent study has highlighted how the power of the pugilistic males fluctuates with the moons. Fatigued by their duels and displays, their claw power wanes. They turn to periods of foraging, where they tone down their usual aggression. This behaviour allows the males the time to build up their snapping strength, and to be ready for the lunar cycle, when their pinching power will once more be at its peak.


McLain, D, Logue, J, Pratt, A & McBrayer, L. (2015) Claw-pinching force of sand fiddler crabs in relation to activity and the lunar cycle. Journal of Experimental Marine Biology and Ecology,  doi:10.1016/j.jembe.2015.06.008

This post originally featured on Biosphere, and can be found here

Image credit: Ivan Kuzimin / Alamy

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