78 EELATIONS BETWEEN DIFFEEENT 



seems not altogether impossible that some of these 

 tame insects may be kept as pets. 



It is from this point of view a very interesting fact 

 that, according to Forel, in the cases of Chennium and 

 Batrisus there is rarely more than one beetle in each 

 nest.^ 



I now come to the relations existing between the 

 different species of ants. 



It is hardly necessary to say that, as a general rule, 

 each species lives by itself. There are, however, some in- 

 teresting exceptions. The little Stenmnma Weshvoodii 

 (PI. III. fig. 3) is found exclusively in the nests of the 

 much larger F. rufa and the allied F.pratensis. We do 

 not know what the relations between the two species are. 

 The Stenammas, however, follow the Formicas when 

 they change their nest, running about among them and 

 between their legs, tapping them inquisitively with 

 their antennae, and even sometimes climbing on to 

 their backs, as if for a ride, while the large ants seem 

 to take little notice of them. They almost seem to be 

 the dogs, or perhaps the cats, of the ants. Another small 

 species, Solenopsis fugax (PI. III. fig. 4), which makes 

 its chambers and galleries in the walls of the nests of 

 larger species, is the bitter enemy of its hosts. The 

 latter cannot get at them, because they are too large 

 to enter the galleries. The little Solenopsis, there- 

 fore, are quite safe, and, as it appears, make incursions 

 into the nurseries of the larger ant, and carry off the 



' Fourmis de la Suisse, p. 426. 



