COMMENSALISM AND SYMBIOSIS 



175 



many different kinds of other insects have been found. 

 Some of these are harmful to their hosts, in that they feed 

 on the food stores gathered by the industrious and provi- 

 dent ant, but others appear 

 to feed only on refuse or use- 

 less substances in the nest. 

 Some may even be of help to 

 their hosts. Over one thou- 

 sand species of these myrme- 

 cophilous (ant -loving) and 

 termitophilous (termite - lov- 

 ing) insects have been re- 

 corded by collectors as living 

 habitually in the nests of ants 

 and termites. The owls and 

 rattlesnakes which live with 

 the prairie-dogs in their vil- 

 lages afford a familiar exam- 

 ple of commensalism. 



92. Symbiosis. Of a more 

 intimate character, and of 

 more obvious and certain mu- 

 tual advantage, is the well- 

 known case of the symbiotic 

 association of some of the 

 numerous species of hermit- 

 crabs and certain species of 

 sea-anemones. The hermit- 

 crab always takes for his 

 habitation the shell of an- 

 other animal, often that of 

 the common whelk. All of 

 the hind part of the crab lies inside the shell, while its 

 head with its great claws project from the opening of the 

 shell. On the surface of the shell near the opening there 

 is usually to be found a sea-anemone, or sea-rose (Fig. 105). 





FIG. 104. A Portuguese man-of-war 

 (Physalia), with man-of-war fishes 

 (Nomeus gronovii) living in the 

 shelter of the stinging feelers. 

 Specimens from off Tampa, Fla. 



