Thursday, July 18, 2013

Fiddler Crab

Waves its long claw like a flag...

There are a number of species (approximately 100) of fiddler crab, also known as calling crab.  All of them are air-breathing, being equipped with enlarged gill chambers, and are therefore found along sandy beaches and on mudflats.  Many species are brightly colored.  The claws of the male crab are out of proportion to each other; one is normal in size while the other is two to four times as long, very swollen and often contrasting in color with the rest of the body - as it acts as a resonance box.

Male fiddler crabs are extremely sensitive to sound vibrations and use their monster claw to draw the attention of neighbors and rivals to themselves and their puny territory.  They wave the claw in the air, occasionally snapping the pincers together.  This dry snapping sound, when performed by swarms of them stationed on the same sandflat, is quite distinctive.  The hen crabs, however, are very ordinary looking.

Each crab digs and occupies its own hole.  The solitary tenants of these holes emerge at low tide but rarely stray far from them except to teach a nosy neighbor a lesson or woo a passing female.  At the slightest disturbance they scramble back into their holes and stay there for some time.  Fiddler crabs, like all species of shore crab, have many enemies - mammals as well as birds - who wait until the tide goes out to move in and feed.  As the tide comes in, each fiddler crab contrives to carry a small disk of mud under its body, and as it descends into its hole, the disk neatly plugs the entrance to the hole, trapping a supply of air inside.  From that point, all the crab has to do is wait patiently for the tide to go out again.

Fiddler crabs live rather brief lives of no more than two years (up to three years in captivity).  Many folks also keep them as pets.  During courtship, the males wave their oversized claws high in the air and tap them on the ground in an effort to attract females. Fights between males will also occur, which are possibly meant to impress the females; if a male loses his larger claw, the smaller one will begin to grow larger and the lost claw will regenerate into a new (small) claw. For at least some species of fiddler crabs, however, the small claw remains small, while the larger claw regenerates over a period of several molts, being about half its former size after the first molt. The female fiddler carries her eggs in a mass on the underside of her body. She remains in her burrow during a two week gestation period, after which she ventures out to release her eggs into the receding tide.

---End of Post "Fiddler Crab"

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