if you learn only 3 things about them ... These colourful crabs are poisonous to eat! Their toxins are NOT destroyed by cooking. They are generally secretive and slow-moving. They are not venomous but it's best not to touch them.

Where seen? This group includes the most colourful large crabs that you might commonly encounter on the shore. The Egg crabs (Atergatis sp.) are often encountered on many of our shores and can be quite common in coral rubble areas. Others are only sometimes seen. They are more active at night, but nevertheless, usually slow moving and always near some hideaway into which they scuttle at the first sign of danger.

Features: Body width 5-10cm. Many members are colourful or strikingly patterned. This probably serves as a warning. The group includes among the most poisonous crabs in Singapore. Their toxins are not destroyed by heat or cooking. These crabs should never be eaten. Eating them can cause Paralytic Shellfish Poisoning which can lead to death. There is no antidote to their toxins.

While these crabs may be poisonous, they are not venomous. That is, they cannot introduce their toxins by stinging or biting. But nevertheless, it's best to leave these crabs alone. For example, those who are allergic might get a reaction by even touching these crabs.

How do they make their toxins? The process is not well understood but it is believed that the poisons are produced by bacteria that live in symbiosis with the crabs. Their toxins are similar to the neurotoxins of puffer fishes, and just as deadly.

What do they eat? Most of these crabs are said to be vegetarians, but at least one was seen chomping happily on a fish.

Human uses: The study of the unique toxins in these crabs may help develop new drugs or achieve better understanding of human health.

Status and threats: Several of these crabs are listed among the threatened animals of Singapore. 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.

• Poisonous Xanthid Crabs, Liomera, Pilodius, Common Rock Crab (Leptodius), Actaeodes mutatus, Red Egg Crab (Atergatis integerrimus) Tan, Leo W. H. & Ng, Peter K. L., 1988. A Guide to Seashore Life. The Singapore Science Centre, Singapore. 160 pp.
• Tetrodotoxin ...an ancient alkaloid from the sea by Jim Johnson on Molecule of the Month of the School of Chemistry, University of Bristol website: lots of details about the toxin's effects, creatures that carry it and how it came about, with LOTS of links to more about tetrodotoxin.
  

• 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).
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• Gosliner, Terrence M., David W. Behrens and Gary C. Williams. 1996. Coral Reef Animals of the Indo-Pacific: Animal life from Africa to Hawai’I exclusive of the vertebrates Sea Challengers. 314pp.