Cancer vs pollex

A couple of days ago I was looking for spiders in a road-side strip of trees at Xametla beach at night, and saw a wee crab sitting in the middle of the road.  I picked it up to save it from being squashed by a vehicle, or the boots of a fellow spider-hunter, and it pinched me on the thumb.  Ungrateful crustacean!  But then to my surprise, the crab separated from its claw and plopped into the palm of my hand while its autotomized chela kept on pinching.

crab that autotomized claw while pinching HPs thumb photo by W Maddison Xametla beach area 25 Feb 2014

Crab and its autotomized claw (photo by W. Maddison)

Dropping appendages is a well-known defense in terrestrial arthropods like harvestmen, and in some vertebrates like geckos, but I had never heard of defensive autotomy in crustaceans.  But, according to Tom Carefoot in his blog A Snail’s Odyssey, it’s quite a common behaviour in crabs.

Hemidactylus frenatus at Chamela Stn with and without tails 26 Feb 2014

Asian house gecko, Hemidactylus frenatus, with and without tails. UNAM Chamela Station, Mexico.

So I’ve now been pinched (crab), stung (ants), or bitten (trombiculid mites, mosquitoes, ceratopogonids) by members of three major groups of arthropods during my stay at Chamela.  Maybe I should next aim to be gnawed on by a pycnogonid.

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