learn only 3 things about them ...
They common on undisturbed shores. Don't step on them!
Only males have an enlarge pincer. It is too big to use
for feeding. Females have two small pincers and thus can
eat twice as fast.
can change colours and species cannot be identified by
seen? Fiddler crabs are common on our natural undisturbed
shores, especially those near mangroves. They are often found in large
numbers. Fiddler crabs are highly sensitive to movement and will vanish
when they feel footsteps on the sand or see shadows. To see them,
wait patiently near their burrows without moving. They will soon re-emerge
and you will be rewarded 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. The enlarged pincer may be as large or larger 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: Eyes mounted on long
stalks give the crab 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.
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. Here's more on how to tell apart
the fiddler crabs commonly seen on our shores.
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.
Role in the habitat: Fiddler crabs
are eaten by many animals higher up in the food chain. The Kingfisher
is among the birds that might snack on them.
Status and threats: The Rosy fiddler
crab (Uca rosea) is listed among the threatened animals of
Singapore. While the other species of Fiddler crabs are not listed
like other creatures of the intertidal zone, they are affected by
human activities such as reclamation and pollution. Trampling by careless
visitors also have an impact on local populations.
can't feed with the enlarged pincer and
have one small pincer to feed with.
Chek Jawa, Oct 04
have two small pincers and
so can feed faster.
Pulau Ubin Jan 04
may be 'right' or 'left' handed.
Pulau Ubin, Jan 04
usually happens inside the burrow,
but this shameless pair was outside!
Kusu Island, May 07
crabs on Singapore shores
species recorded for Singapore
Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity
in red are those listed among the threatened
animals of Singapore from Davison, G.W. H. and P. K. L. Ng
and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened
plants and animals of Singapore.
**from Ng, Peter K. L. & N. Sivasothi, 1999. A Guide to the Mangroves
of Singapore II (Animal Diversity)
crabs commonly seen awaiting identification
Species are difficult to positively identify without
On this website, they are grouped by external features for convenience
(Austruca) annulipes (Porcelain fiddler crab)
Uca dussumieri=^Uca (Tubuca) dussumieri
Uca forcipata=Uca manii=^Uca (Tubuca) forcipata
(Tubuca) rosea (Rosy fiddler crab) (EN:
**Uca paradussumieri=^Uca (Tubuca) paradussumieri (Purple
Uca vocans=^Uca (Gelasimus) vocans
(Orange fiddler crab)
- Ng, Peter
K. L. and Daniele Guinot and Peter J. F. Davie, 2008. Systema
Brachyurorum: Part 1. An annotated checklist of extant Brachyuran
crabs of the world. The Raffles Bulletin of Zoology. Supplement
No. 17, 31 Jan 2008. 286 pp. (Online
PDF on the Raffles Bulletin of Zoology website.
- Jocelyn Crane.
Crabs of the World. Ocypodidae: Genus Uca, Princeton
University Press. 737pp
- Edward E.
Ruppert, Richard S. Fox, Robert D. Barnes. 2004.Invertebrate
Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963
- Lim, S.,
P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life
and Times of Labrador Beach. Division of Biology, School of
Science, Nanyang Technological University & Department of Zoology,
the National University of Singapore. 160 pp.
- Wee Y.C.
and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore.
National Council on the Environment. 163pp.
- Ng, P. K.
L. & Y. C. Wee, 1994. The
Singapore Red Data Book: Threatened Plants and Animals of Singapore.
The Nature Society (Singapore), Singapore. 343 pp.
- Jones Diana
S. and Gary J. Morgan, 2002. A Field Guide to Crustaceans of
Australian Waters. Reed New Holland. 224 pp.
- Davey, Keith,
1998. A Photographic Guide to Seashore Life of Australia.
New Holland, Australia.144 pp.
Michael, 1997. Mangroves:
The Forgotten Forest Between Land and Sea. Tropical Press,
Malaysia, 200 pp.
- Morton, Brian
& John Morton, 1983. The
Sea Shore Ecology of Hong Kong.
Hong Kong University Press. 350 pp.