78 RELATIONS BETWEEN DIFFERENT 
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 Chenniwm 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 Stenamma Westwoodii 
(Pl. 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 antennz, 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 fugaw (Pl. 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 tne larger ant, and carry off the 
1 Fourmis de la Suisse, p. 426. 
