Creature of the Month – Peracca’s Land Crab (Geosesarma perracae)

Crabs are generally covered with a thick exoskeleton and armed with a single pair of claws.  Crabs that most of us are familiar with are those found in the sea.  However, not many people know that, in Singapore, there are about 6 species of crabs that live in fresh water.   They are mostly found in steams and swamps in our forested areas.  Three of these species (namely Singapore Freshwater Crab, Johnson’s Freshwater Crab & Swamp Forest Crab) are believed to be endemic to Singapore which means that they can only be found in Singapore and nowhere else!  All the 6 species are said to be either locally vulnerable or critically endangered.

(Johnson's Freshwater Crab & Lowland Freshwater Crab)

(Johnson’s Freshwater Crab & Lowland Freshwater Crab)

Of these fresh water crabs, Peracca’s Land Crab (Geosesarma perracae) & Little Land Crab (Geosesarma nemesis), in my opinion, are the most beautiful because of their brightly red coloured appearance.  Both species are tiny crabs of about 15 mm in size.  These non-marine crabs can be found in streams in burrows of 5-20 cm deep.  They look almost identical and I have difficulty differentiating them.  Geosesarma nemesis is recorded to be restricted in Bukit Timah Nature Reserve & Bukit Gombak areas while Geosesarma perracae has wider distribution range which include Bukit Timah Nature Reserve, Upper Peirce & Macritchie Reservoir forest.

(Geosesarma perracae, male & female)

(Geosesarma perracae, male & female)

The above is most probably a pair of Peracca’s Land Crabs as this was photographed in Upper Peirce Forest.  The male on the left has a brightly chilly red colour while the female has duller brownish colour.  Let’s us take a closer look at this handsome male crab.

(Geosesarma nemesis, male)

(Geosesarma perracae, male)

I was fortunate to photograph this male in standing pose. Crabs don’t usually stay in this position for long as it means they are preparing to move somewhere else.

(Geosesarma nemesis, male, in standing pose)

(Geosesarma perracae, male, in standing pose)

Here is a dorsal view:

(Geosesarma nemesis, male, dorsal view)

(Geosesarma perracae, male, dorsal view)

Women are normally more attractive looking than men but strangely, in the insect world such us dragonflies, butterflies, etc, it is the males that are usually the more good-looking ones. The females of the Peracca’s Land Crabs are no exception. They look plain and dull when compared to their charming males.

(Geosesarma perracae, female)

(Geosesarma perracae, female)

(Geosesarma perracae, 2 females)

(Geosesarma perracae, 2 females)

Given the fact that Chilly Crabs and Black-Pepper Crabs are Singaporean’s favourite dishes, I believe some of us may be interested to know whether these freshwater crabs are edible or not. The answer is a definite NO for two simple reasons. Firstly, there are so little fresh in such tiny crabs that doesn’t justify the effort of searching through our forests to catch them for food. Besides, this species is already classified as locally vulnerable and with the plan to construct the Cross Inland Line that cut through the southern portion of the Central Catchment Nature Reserve, between Upper and Lower Peirce and MacRitchie Reservoirs, it could potentially lead to extinction in Singapore! Hence, catching of these crabs for human consumption is strongly discouraged.

References:
A. First Record in Singaore of a Nepenthiphilous Crab, Geosesarma perracae
B. Have a Crabby National Day

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2 thoughts on “Creature of the Month – Peracca’s Land Crab (Geosesarma perracae)

  1. believe you mentally slipped and didn’t really mean to say insect 😉

    anyway wonderful pictures esp in situ

    “Women are normally more attractive looking than man but strangely, in the insect world, it is the males that are the more good-looking ones.”

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