266 



THE NORTH AMERICAN GRASSLAND 



intervals develops in enormous numbers to constitute a plague, some- 

 times as the migratory form, M. m. spretus. In the grasshopper years 

 of the seventies, this form moved eastward in great swarms that de- 

 stroyed crops over wide areas. Most of these grasshoppers deposit 

 their eggs in the soil, and quantities of them are destroyed by ground 

 squirrels, mice, etc. It has been estimated that grassland insects may 

 devour more forage than the cattle that might be grazed on the same 

 area (cf. Isely, 1904). 



Fig. 60. — Ant garden near Colorado Springs; ten other anthills are visible. The 

 presence of the forb {Cleome sernilata) is due to ant coactions. (Photo by 



Edith Clements.) 



Robber flies are usually very numerous, and also the various flies 

 that originally bred in the buffalo droppings. Hemiptera are not well 

 represented, at least as to number of individuals. Harvester ants are 

 often conspicuous (Fig. 60). The ground beetles familiar in the 

 moister lowland prairie are displaced by Tenebrionidae. The ground- 

 inhabiting tiger beetles, such as Cicindela purpurea graminea Schp., 

 auduhonii Lee, pulchra Say, and obsoleta Say, all of which make ver- 

 tical burrows in the soil, occur in open spaces among the grasses. 



Serai Stages. Over much of the mixed prairie area, the bottom 

 lands of the small rivers and larger creeks are occupied by tall grasses. 



