HABITS OF FIDDLER CKABS. 



B}' A. S. Pearse, 

 Vnivemity of Wisconsin. 



Fiddler crabs are of unusual interest on account of their striking 

 sexual dimori^hism. The male bears an enormous claw on one side 

 of the body Avhich is in striking contrast to its feeble mate on the 

 opposite side, while the female has two little chelipeds like the small 

 claw of the male. Since the time of Darwin (1874) these crustaceans 

 have been believed to furnish evidence of sexual selection. The great 

 claw and bright coloration of the male differ markedly from the com- 

 paratively dull dress and small bilaterally symmetrical chelipeds of 

 the female. Alcock (1892, 1900, 1902) is convinced that ( 1900, p. 351) : 



lu oue species, at any rate (Gclasiinus annuUi)es), the males, which are 

 greatly in excess of the females, use the big and beautifully colored cheliped 

 not only for fighting with each other, but also for "calling" the females. 



Fig. 1.— Uca pugnax, males and females. Woods Hole, Mass. 



According to the same writer (1892), Milne-Edwards describes a 

 South American species, in which the male and female lived together 

 in a single burrow, the former closing the domicile with his large 

 chela. But Caiman (1911) is apparently not convinced that the 

 uses of the great chela of male fiddlers has been demonstrated, for he 

 says (p. 106) : 



What the precise use of this enormous claw may be does not seem to be quite 

 certainly known. It is said to be used as a weapon by the males in fighting 

 with one another, but it seems too clumsy to be A-ery efiicient for this purpose. 

 It is often brilliantly colored, and has been supposed to be a sexual adornment. 



The writer was first attracted to the study of the fiddlers by the 

 great colonies of gaudy species which swarm along the beaches of the 



415 



