117 



equal A porous subsoil is also conducive to the well-being of 



insect life, in that the rain can quickly penetrate, and, as it passes 

 through, air is drawn into the more superficial layers in order to take 

 its place. Hence a reason why soil insects are only rarely found in the 

 deeper subsoil ; for the increased amount of moisture, together with the 

 decrease in aeration, is decidedly detrimental to their activities." 



The density, moisture, solutions, and ventilation of the soil, its 

 fresh and decaying vegetation, make conditions possible both for a 

 population consisting of vegetable feeders and, preying largely upon 

 them, a series of predaceous and parasitic associates. 



It is desirable that the prairie ground fauna should be made the ob- 

 ject of special investigation, particularly from the standpoint of soil 

 solutions, moisture content, ventilation, humus content, and the in- 

 fluence of the living vegetation. For this reason several papers are 

 here mentioned which will be valuable in such a study. Diem ('03) 

 has made an elaborate quantitative study of the ground fauna of the 

 Alps. He studied a variety of conditions, including pasture, meadows, 

 and coniferous forest soils. He describes his methods of study and 

 gives many references to the literature. Other papers which should be 

 studied in this connection are by Dendy ('95), Cameron ('13), Hotter 

 ('98), and particularly those by Holdhaus ('10, 'iia, 'lib). Banta's 

 ('07) paper on cave animals will also prove valuable because of the 

 close relation of cave animals to those living in the smaller openings in 

 ordinary soil. 



Near the soil surface, among the stools of grass and on the ground, 

 vegetable litter is most abundant, and humidity is high, evaporation 

 slow, and the temperature lower and also more equable than higher 

 up. It is in this layer that a vast number of animals hibernate; and 

 in it also many, active at night, are hidden during the day. In this 

 layer live the animals which feed largely on organic debris. Bumble- 

 bees often build their nests at this level, or in depressions in the ground. 

 Some of our species of Bombus may nest deep in the soil and ventilate 

 the nest by vibrating their wings, as do certain European species ( Sla- 

 den, '12, pp. 47-49). This is a very interesting response to a subter- 

 ranean life and merits investigation. 



2. The Prairie Vegetation Community 



Above the surface of the soil, among the vegetation, quite another 

 environment exists. This varies greatly not only with the character of 

 the substratum but also with the character and density of the prairie 

 vegetation. The fertility of the black soil, and the rapidity with which 

 it is occupied by vegetation, makes areas of bare soil of short duration. 



