Safety 



65 



never feed when their burrows are covered with water. They browse 

 about in great armies over exposed beaches, but when the tide rises, 

 each crab retreats into its burrow, plugs up the opening, and re- 

 mains safe inside until the water recedes again. On rough eroded 

 beaches, like those on the shores of Bermuda and Japan, little snails 

 without shells (Onchidium) live in the crevices. These never come 

 out to feed when the tide covers their homes (Arey & Crozier, 1921; 



Fig. 1 1. When the rising tide is about to cover the mouth of a tid- 

 dler crab's burrow the owner digs a plug and closes the mouth until 

 the tide recedes again. 



Pearse, 1931a) . The burrowing crustacean which is often called the 

 beach flea (Talorchestia) , though it lives a semi-terrestrial life 

 along the shore and has little or no toleration for fresh water, 

 avoids the sea (Verwey, 1927) . The ghost crab (Ocypode) lives in 

 a burrow on land and commonly hides by throwing sand over 

 its body so that nothing but its stalked eyes protrude (Cowles, 

 1908) . It commonly hunts along sandy beaches at night. If it is 

 then pursued, it may dash into the ocean for a short time but does 



