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- 
Fie 104.—A Portuguese man-of-war 
crab always takes for his (Physalia), with man-of-war fishes 
habitation the shell of an- (Nomis gronout) living: ‘in the 
2 shelter of the stinging feelers. 
other animal, often that of Specimens from off Tampa, Fla. 
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 often to be found a sea-anemone, or sea-rose (Fig. 105). 
