THE GEOGRAPHICAL DISTRIBUTION OF ANTS. 15? 



we find that the colonies are not uniformly distributed over their 

 whole range, but only in particular stations, or habitats, showing that 

 these insects, like plants and many other animals, depend very inti- 

 mately for their welfare on precise physical and organic environments, 

 such as the nature of the soil and vegetation, the amount of mois- 

 ture and the exposure to sunlight. Colonies that happen to be estab- 

 lished in unfavorable localities take on a more or less depauperate 

 appearance. This is indicated by their scarcity and the small size of 

 the colonies and individuals, and is particularly noticeable at the very 

 limits or just beyond the limits of the normal range of a particular 

 form. I find that according to the station inhabited by the various 

 species, subspecies and varieties, at least in North America, we may 

 distinguish the following ethological groups, or associations: 



1. The woodland, or sik'icolous association, comprising the species 

 that inhabit our moist, shady northern and eastern forests. With the 

 extinction or drainage of these forests or the removal of the under- 

 growth, this characteristic, and in many respects, very primitive fauna 

 rapidly disappears. 



2. The glade, or nemoricolous association, comprising the ants that 

 prefer open, sunny woods, clearings or the borders of woods. A por- 

 tion of this fauna maintains itself even in the gardens and parks of 

 our cities. 



3. The field, or cespiticolous association, comprising the ants that 

 prefer to nest in grassy pastures and lawns, in situations exposed to 

 the full warmth and light of the sun. 



4. The meadow, or pratincolous association, comprising the ants 

 which inhabit low, grassy meadows or bogs. 



5. The heath, or ericeticoloits association, comprising the ants that 

 inhabit rather poor, sandy or gravelly soil exposed to the sun and 

 covered with a sparse growth of weeds or grasses. 



6. The sand, or arcnicolons association, comprising the ants that 

 prefer to nest in pure sand. 



7. The desert, or deserticolous association, comprising the ants that 

 inhabit the dry, open deserts and plains. 



A few of our species, like Lasins aincricanns and Formica snb- 

 scricea, are so adaptable that they occur more or less abundantly in 

 all or nearly all of the above stations. Owing to intergradation of 

 these stations in some places, there is, of course, a corresponding 

 mingling of forms. Thus certain species, like Monomoriuin minimum, 

 seem to belong indifferently either to the heath or sand fauna. In the 

 deserts of the Southwestern States these two faunas may either mingle 

 or be sharply separated from each other. In the Northeastern and 



