learn only 3 things about them ...
They only seen at night. But the large holes to their
burrows are commonly seen on sandy shores near the high
Their burrows are deep. Don't try to dig them up.
can move very fast.
seen? This large but elusive crab is common on many of
our shores. Yet, it is hard to spot. It probably got its common name
because it is active only at night, and it moves so swiftly over the
sand that you usually literally only get a ghostly glimpse of one.
Often all you will see of the crabs during the day are their large
holes marking the entrance to their burrows . These are usually on
sandy beach near or above the high water mark. It is said that
when tunneling out their burrow, the crab carry sand to about 50-100
cm away from the burrow entrance, then toss the sand as far as it
can. This behaviour probably explains the typical "spray"
pattern of sand around the burrow. The burrow can be quite deep. So
please don't try to dig up the crab.
Features: Body width 6-8cm. Body
squarish box-like. Usually bluish grey with brown markings on the
back, often in the shape of an "H". But a variety of other
patterns also seen. Pincers long, downward pointing often with white
or pale claws. Has a vertical ridge on the inside of the 'palm' that
produces a rasping sound when rubbed against the rough surface of
the face. This is probably done to declare their territory. Legs long
with pointed tips. Large eyes on short stalks which can fold away
into grooves on the body when the crab burrows into the sand. Adult
crabs have a characteristic tall skinny point or 'horn' on top of
each eye (called the stylophthalmous), usually darker in colour. The
horn is shorter in females and absent in juveniles (2.5cm or smaller).
A study found that
juveniles can change their body colour and pattern to match the surrounding
sand, usually becoming lighter during the day and darker at night.
Ghost crabs are well adapted for life out of water and are among the
few marine creatures that roam the beaches at low tide, particularly
at night. They run rapidly on the sand and can burrow quickly into
wet sand. They can stay for a long time away from the sea because
they can absorb water from the wet sand through special hairs on the
base of their legs by capillary action.
to the Smooth-eyed ghost crab
(Ocypode cordimanus) which is rarely encountered.
Speedy Ghosts: Ghost crabs can
really run fast! As suggested by their scientific name ("Ocy"
means swift and "podi" foot in Greek). They literally fly
over the sand and their movement has been described as a small leaf
blowing over the sand surface. In fact, they may be among the fastest
land creatures, moving at 100 bodylengths per second. In comparison,
the cockroach does 50 bodylengths while the cheetah does a sluggish
10 bodylengths. Ghost crabs are only beaten by tiger beetles which
do 171 body lengths when they are really scared. Being fast moving
creatures, Ghost crabs have excellent eyesight to see where they are
What does it eat? At low tide,
this scavenger is very active at night, scurrying everywhere on the
shore. It has been seen eating all manner of recently dead animals
on the shore from fireworms to fish, shrimps and even other crabs.
It may also hunt small animals and clams and snails near the water's
edge. Near the flotsam left on the high water line, we can also sometimes
see little scratch marks probably made by ghost crabs checking the
line for edible titbits.
A slot on the body for
the eye stalk to 'fold' away.
Tanah Merah, Aug 09
Vertical ridge and tiny
on the inside of the 'palm'.
Tanah Merah, May
Typical burrow near the
high water mark.
Changi, Apr 05
Some have white pincers,
one much bigger than the other.
Sisters Islands, Jan 06
No 'horns' on the eyes: young one?
East Coast, Jun 06
Eating a shrimp.
Tanah Merah, Aug 09
Eating another crab.
Pulau Hantu, Nov 03
Eating a fish, probably a goby.
Tanah Merah, Sep 10
ghost crabs on Singapore shores
- 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)
- Jones Diana
S. and Gary J. Morgan, 2002. A Field Guide to Crustaceans of
Australian Waters. Reed New Holland. 224 pp.