HABITS OF FIDDLER CRABS PEARSE. 425 



GENERAL CONSIDERATIONS. 



Fiddlers treat other animals with suspicion. Any large moving 

 object causes them to retreat at once to their burrows, although they 

 soon emerge again if the object is not near at hand. Most crabs re- 

 treat into their holes when a man approaches within 15 meters, but if 

 one is careful not to make any quick movements he may sit apparently 

 unnoticed within a couple of yards of an active fiddler for hours at a 

 time. Large adult crabs like Sesarma hidens are avoided, but small 

 crustaceans of any species are at once attacked. Any strange animal, 

 however small, is avoided; the writer once saw a small hermit crab, 

 by moving quickly along the edge of the rising tide, cause every 

 fiddler near to run for its hole. The fiddler's burrow furnishes a re- 

 treat from many enemies, and his speedy reaction toward it in re- 

 sponse to all movements in his field of vision would help protect him 

 from the herons, snakes, skinks, frogs, toads, and fishes that com- 

 monly hunt along the shores of the estuaries. 



In reacting to its suiTOundings a fiddler crab apparentlj^ uses its 

 senses of sight and touch most, although the recognition of chemical 

 substances may be important in securing and selecting food. The 

 eyes are very quick to note any movement in the landscape ; they are 

 held straight upward, except when their stalks are being cleaned or 

 when a crab is entering a burrow. Feeding probably depends mostly 

 upon the tactile and chemical senses, for the usual position of the 

 eyes is such that the small chelae can not be seen as they pass food 

 to the mouth. Such loud noises as whistling, hand clapping, gun- 

 shots, and locomotive whistles produced no apparent reaction from 

 the fiddlers, nor did the stridulation of the large decapod, Thalassina 

 anomala (Herbst), that builds its burrows among them in the 

 Philippines. 



Although fiddler crabs live together in enormous colonies, they 

 show no cooperation with one another, nor do they manifest any 

 tendency toward such communal existence as that displayed by some 

 other arthropods; for example, ants, bees, wasps, and termites. In 

 this they agree with other crustaceans, for, though the animals of 

 this class exhibit an endless variety of structural adaptations suited 

 to various habitats and modes of life, none of them has taken advan- 

 tage of the opportunities offered by a cooperative communal associa- 

 tion among members of the same species (except in some instances 

 in which the male is intimately associated with the female). Al- 

 though the females of many species carry their eggs and newly 

 hatched young for a time, the association of the young with their 

 mother is nominal, for she never feeds or cares for them. The strug- 

 gle for existence is nowhere more apparent than in the midst of a 

 fiddler crab colony. Each individual jealously guards the area about 



