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Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Brachyurans > Superfamily Ocypodoidea
Sand bubbler crab
Scopimera and Dotilla spp.
Family Dotillidae
updated Dec 2019
if you learn only 3 things about them ...
They are everywhere on the sandy shore at low tide. Don't step on them!
The tiny sand balls are processed sand. Not excretion or from burrowing.
They are related to fiddler crabs.

Where seen? This tiny ball-shaped crab is often seen on our sandy shores, just below the high water line. Resembling the little sand balls that it creates all over the shore at low tide, the crab itself is often missed. It is also very nervous and disappears instantly into its burrows at the slightest sign of danger. To spot these crabs, you will have to wait quietly next to their burrows. Stay low and avoid casting a shadow over the burrow. In a few minutes, they will appear. If you stay still, they will go about their amusing business. Do avoid stepping on sand balls on the shore as you might be stepping on a little crab!

Features: Body width 1-1.5cm. Body spherical with eyes on short stalks. These can fold away into grooves along the bodies when the crabs scurries into its burrow. Pincers long, flattened and downward-pointing. Males may have larger and longer claws than females. The crab is generally the same colour and pattern as sand. It has stiff hairs on the legs which absorb water from the wet sand. This allows the crab to stay out of water for some time.

Chek Jawa, Feb 05

Mating sand bubbler crabs held in the hand.
Chek Jawa, Sep 03
.

Shore covered with tiny balls of sand
created by busy sand bubblers.

Chek Jawa, Apr 07

What does it eat? The sand bubbler crab eats the thin coating of edible particles on sand grains. Sand grains are scraped up with the downward pointing pincers and brought to the mouthparts that sift out these tiny particles. The shifted sand is then discarded in a little ball. As it processes sand, a little path is scraped out from the burrow entrance. Little balls of sifted sand is piled up on either side of this path.

Sand patterns: Sand bubbler crabs are responsible for the delicate patterns of tiny balls on the sandy shores at low tide. The crabs emerge as soon as the tide recedes. You can almost tell how long the tide has been out by the patterns of their sand balls. The more intricate the pattern of sand balls, the longer the tide has been out.

Chek Jawa, Mar 05

Creating little balls of sand.

Status and threats: Our sand bubbler crabs are not listed among the threatened animals of Singapore. However, 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.
Sand bubbler crab (Scopimera sp.)

Sand bubbler crabs on Singapore shores
On wildsingapore flickr

Other sightings on Singapore shores


Coney Island, Jun 20
Photo shared by Richard Kuah on facebook.

Coney Island, Oct 20
Photo shared by Richard Kuah on facebook.


Chek Jawa, Jul 16
Photo shared by Heng Pei Yan on facebook.

Chek Jawa, Jun 17
Photo shared by Marcus Ng on facebook.


Berlayar Creek, Oct 15
Photo shared by Loh Kok Sheng on facebook.

Cyrene Reef, Feb 16
Photo shared by Heng Pei Yan on facebook.
Terumbu Hantu, Jul 19
Photo shared by Toh Chay Hoon on facebook.

Links References
  • 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.
  • 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.
  • Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore. National Council on the Environment. 163pp.
  • Edward E. Ruppert, Richard S. Fox, Robert D. Barnes. 2004.Invertebrate Zoology Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963.
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