Uca spp.

Uca spp. (commonly known as Fiddler Crab)

Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Malacostraca
Order:	Decapoda
Infraorder:	Brachyura
Family:	Ocypodidae
Genus:	Uca Leach, 1814

Where seen?

Fiddler crabs are common on our natural undisturbed shores, especially those near mangroves. They are often found in large numbers. For those that bother to look for them, fiddler crabs reward with their amusing behaviour: frantically feeding, squabbling and courting, all at the same time.

Features:

Body width 2-3cm. The male fiddler crab has one huge pincer, often highlighted in a bright colour that contrasts with his shell. The enlarged pincer may be as large and as heavy as the rest of the crab's body! This enormous pincer is not used to hunt or crush food. It is too small to effectively fend off most predators. Instead, it is used to attract females and to intimidate rival males. The male waves his large pincer in a style and rhythm unique to his species in order to attract the ladies. Fiddler crabs got their name for this behaviour, which resembles a musician playing on his fiddle.

Looking out:

The eyes of a Fiddler crab are mounted on long stalks giving it a good all-round view on the flat terrain where they are usually found. When the crab scuttles back into its burrow, the eyestalks fold down into grooves along the body. Fiddler crabs are highly sensitive to movement and will scurry off at the slightest hint of danger.

Colourful costumes:

Fiddler crabs can change colours. Sometimes, they appear different at night and during the day. In some species, the males brighten up during mating season. This makes it challenging to identify the different species of fiddler crabs by their colours alone. The species are generally distinguished by the structure of their pincers rather than by colours alone.

Breathing air:

Fiddler crabs cannot swim and prefer to breathe air. So at high tide, they hide in their burrows, plugging the entrance with a ball of sand to trap some air inside. However, they need water to keep their gill chambers wet as well as to process their food. They absorb water from the wet sand through hairs on their legs.

What do they eat?

Fiddler crabs eat the thin coating of detritus on sand grains. They scoop sand to their mouthparts with tiny feeding pincers that are spoon shaped and fringed with hairs. The bristle-like mouthparts scrape the sand grains clean of any edible titbits. A male fiddler crab cannot feed with his huge pincer and has only one much smaller feeding pincer. Females, however, have two feeding pincers and can thus feed much faster.

Fiddler babies:

When a male Fiddler crab succeeds in persuading a female to mate with him, they retire into his burrow. The female may remain there until the eggs hatch. The eggs hatch into free-swimming larvae that drift with the plankton, changing into yet another form before settling down and developing into Fiddler crabs.

Credit: http://www.wildsingapore.com/wildfacts/crustacea/crab/ocypodoidea/uca.htm