Habits: Fiddler crabs spend most of their time out of the water, feeding on the shore when the tide is out. Staying close to the long burrows they excavate in the sand, the crabs retreat into the holes at the sign of any danger. When the tide is in, the crabs bury deep into their individual burrows, safe inside a pocket of air. Although fiddler crabs spend all their time on land, they breathe through fish like gills that need to be kept moist.

Predators: At its larval stage, the fiddler crab is eaten by a wide variety of predators, such as the flamingo, which scoops up the larvae by the thousands. Adult crabs also have many predators. Birds like the frigate and tern swoop down and snap them up. The whimbrel chases them across the beach, breaking off their legs before eating them. Foraging mammals dig them out of their burrows.

Food and Feeding: Fiddler crabs use their front claws to feed by scooping up sand and mud which they pass to their mouthparts. They eat the algae that they separate from the grains of sand and mud. The non edible particles are ejected on the seashore in the form of tiny, pea size pellets. Because sand and mud contain little organic material, the crab must feed continually to survive. Male fiddler crabs spend twice as long feeding as the females.

Breeding: The male fiddler crab uses his large, brightly colored claw to protect his territory from rival males and to attract females. He will display his claw to a female and then retreat into his burrow, where the female follows him to mate. After mating, the female deposits several hundred fertilized eggs into the sea. The crab larvae soon hatch and spend the first part of their lives as part of the plankton (microscopic plants and animals) that floats in the ocean. As the larvae grow and molt, they begin to resemble tiny crabs and are eventually washed up on the beach. Young fiddler crabs are miniature versions of the adults. They excavate their own burrows, but will not mate until they have reached their full size and become sexually mature at 1-2 years. 

Key Facts:
Sizes:
Length: Up to 1-2 in.
Length of male’s claw: Up to 2 in.

Breeding:
Sexual maturity: 1-2 years
Mating: Several times a year, depending on species, location, and the tides
No. of eggs: Several hundred
Incubation: About 7-10 days. Eggs hatch into tiny planktonic larvae

Lifestyle:
Habit: Solitary, shore living
Diet: Organic particles scraped from grains of sand or mud

Related species: There are many different types of fiddler crab, belonging to the genus Uca. Some species can be identified by the particular form of their mating display.
Distribution: Found throughout the warmer areas of the world, including the shores of the Pacific Ocean, the South Atlantic, and the Mediterranean.
Conservation: Fiddler crabs are found in larger numbers throughout their range. The main danger to their survival is the increasing level of marine pollution worldwide.

The Fiddler Crab’s Claws: The male fiddler crab’s claw is greatly enlarged and brightly colored. By displaying his claw to a female, the male hopes to lure her into his burrow to mate. By waving his claw at other males, he warns them to stay away from his territory. He also uses it when fighting with rival males.
The female’s claws are of regular size, enabling her to gather food more easily than the male.

Did You Know: 
In certain species of fiddler crab, the males have an enlarged right claw, while in others they have an enlarged left claw.
As the fiddler crab grows, it must shed its outer shell, or molt. Because the crab’s new shell is still soft while molting, it seeks the shelter of its burrow, where it is safe from most predators.
The largest crab in the world is the giant spider crab, which lives at great depths off the coast of Japan. Its shell is only 12 inches across, but its legs can stretch as far as 6 feet.

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