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Fiddler Crab — printable fact sheet
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Fiddler Crab
Uca pugnax
A male fiddler crab has one claw that is grotesquely, uselessly large — in some species it makes up close to half his entire body weight — and one small ordinary one. The big claw cannot feed him. Only the small claw can perform the crab's actual meal, which is a delicate sortin…
Did you know?
- Despite their small size, fiddler crabs are crucial ecosystem engineers—by burrowing, they improve soil aeration and nutrient cycling in coastal habitats.
- In some species males build a chimney, hood or pillar of mud beside the burrow, which appears to work as a landmark that draws the eye of females scanning across the flat. A fiddler crab's colour changes on a circadian and tidal cycle, darkening by day and paling at night, controlled by hormones — an effect so reliable it was used in early chronobiology research. Fiddler crabs sort sediment so thoroughly that a large colony visibly turns over the whole surface of a mudflat, aerating it and shaping the sediment chemistry. Females choose males partly on how vigorously and how fast they wave, so the display is a genuine advertisement of stamina.
What I learned
Draw the fiddler crab
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