I found this tiny hermit crab scrabbling around in the seaweed and seashell debris of a sandy tide pool beneath Rhossili cliffs. I thought at first that it was just a very small, immature, specimen of the common hermit crab (Pagurus bernhardus Linnaeus) but as soon as I picked it up for a closer look I could see that it was something special because it had a large claw (cheliped) on the left instead of the right. There is only one species with this characteristic – the south-claw hermit crab, Diogenes pugilator (Roux). The mature specimens have a greenish carapace no greater than 11 mm in length.
According to Hayward and Ryland (1998) this crab lives in fairly sheltered sandy bottoms from low water spring tide level down to 35 m, on south and west coasts of the British Isles where it is described as common. It also occurs elsewhere from Holland to Angola, Mediterranean, Black Sea, and Red Sea. Mullard (2006) provides more information, saying that D. pugilator is only found in a limited number of places in Britain and Ireland because it is primarily a warm-water species and may be worthy of further study in relation to climate change since there are signs of it extending its range. It was first recorded in Britain “at Worms Head” from specimens provided by L. W. Dillwyn of Sketty Hall in Gower to Spence Bate in 1850 who described it in Annals and Magazine of Natural History.
The crab can quickly bury itself in clean, well-sorted sand on a gently shelving moderately exposed beach facing southwest where conditions are less turbulent than on steeper beaches. This crab has an interesting extra way of gathering food, in addition to scavenging or eating sediment. While mostly buried in the sand, it can sweep its hairy antennae around in an almost circular motion as a net to capture small edible particles from the water.
References
Hayward, P. J. and Ryland, J. S. (eds) 1995 (revised edition 1998) Handbook of the Marine Fauna of North-West Europe, Oxford University Press, New York, pp 434-437, ISBN 0-19-854055-8.
Mullard, J. 2006 Gower, The New Naturalist Library, Collins, London, pp167-168, ISBN0-00-716066-6.
Jessica's Nature Blog 
Pugnacious little critter!
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He was certainly hyperactive and a problem to focus on because he was so small. I had difficulty keeping him in the palm of my hand.
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Fascinating find!
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Thank you, Centralohionature.
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How lovely! What a cute little thing. I didn’t know there were different species of hermit crab.
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Thank you. Yes, it seems that in Northern Europe there are quite a few; 18 species are recorded for Britain in seven genera but the most commonly found one is Pagurus bernhardus.
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I would SO like to be named Diogenes Pugilator. A most memorable appellation!
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It is a terrific name, isn’t it? This pugnacious little crab is named after the philosopher Diogenes of Sinop who embraced poverty and eschewed possessions, reputedly lived in a large clay wine jar, some say barrel, and fighting accepted beliefs and customs.
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Yes – indeed he was perhaps the first pugnacious philosopher. He once went 6 rounds with Plato until the latter submitted (later rationalising this as a glorious victory). If you can be bothered you will see in my tedious profile (under Welcome tab, Profile, Philosphy) that I live by the precepts of Diogenes…
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My name is Josh. I am an American in South Korea. I was looking in tide pools on the southern coast of Korea in the city of Yeosu. I found some tiny hermit crabs and I took a closer look and they closely resemble the crabs you are talking about. I have some Macro DSLR photos of the crabs I found. I think its interesting because it fits the climate but is far away from the normal area.
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Hello Josh. I am entirely unfamiliar with the species of hermit crab which live in the place you visited. It is possible that the species you photographed has similar characteristics to the Diogenes pugilator that I saw in South Wales – even to the extent of having a dominant front left claw instead of the right one. It would be best to contact a local Korean museum or university department for an accurate identification. Sorry I can’t help you further.
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Lots of these (I think ) at low tide on Broad Haven beach Pembrokeshire on Sunday, have been reading up about them, our video grabs are mostly of them running about in the tide, sometimes rolling for extra speed? possibly mating? and then burying themselves in the sand, just as you describe here. Thank you for all the info. Great post! Jo
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Great to think of lots of these at Broad Haven too. Did you check that the animal’s left claw was the largest claw? Glad the post was useful.
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Yes, it is very distinctive, and being a left handed person, I noticed it 🙂
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