115 



have been recorded by Hart, and his observations ampHfied by Vestal. 

 In the black soil area many observations have been made by Forbes 

 C94) on the life histories and habits of certain species of economic 

 importance, particularly those injuring corn and grasses in the soil. In 

 his studies are included many insects, such as elaterid larv^, aphids, 

 ants, and white-grubs. The physical conditions of life here yet await 

 careful investigation. 



A very large number of the animals living on and above the sur- 

 face of the soil spend a part of their lives within it. Thus among the 

 Orthoptera, the acridiids lay their eggs in the soil — this is probably 

 true of most of the beetles ; and even the parasitic animals often spend 

 most of their life in the soil with their hosts. This is true also of the 

 wasps and a great number of hibernating animals, and of a large num- 

 ber of grass-inhabiting, and other, Lepidoptera. Such characteristic 

 flies as the asilids and bombyliids spend much of their life in the soil, 

 as do many other flies, at least during their pupal period. It is very 

 probable that upon the original prairie a large number of noctuid and 

 crambid moths and tipulid and elaterid larv« inhabitated the prairie 

 sod, and with them, of course, were associated their enemies — preda- 

 ceous beetles, and parasitic flies and Hymcuoptera. For an account of 

 grass-feeding crambids Felt (94) and Fernald ('96) should be con- 

 sulted. 



The stage of development, structure, and behavior of soil-inhabit- 

 ing animals are often quite different from those living above the sur- 

 face. Some kinds, as pupae or adults, have spines or setae, which enable 

 them to wriggle in the soil, as, for example, do the pupal asilids or the 

 adults of My due and Tiphia. Locomotion in such a dense medium 

 is attended by many difficulties, and it is not surprising that animals 

 living here have peculiarities of structure and behavior, and that a 

 large number are relatively sedentary. 



In the discussion of the ventilation of habitats, attention was called 

 to the fact that soil-inhabiting animals probably possessed considera- 

 ble resistance to an abundance of COo and to a lack of oxygen. We 

 are all familiar with the abundance of earthworms, Lunibricus and its 

 allies, crawling upon the surface and entrapped upon our walks and 

 pavements after prolonged rains. In these cases the saturation of the 

 soil has driven out the air. Apparently the earthworms are relatively 

 less resistant to the lack of oxygen than many other soil animals, for 

 they come to the surface in a much more marked degree. Since earth- 

 worms live in burrows, have an easy route to the surface, and are pos- 

 sessed of good powers of locomotion, they contrast strikingly with 

 many other sedentary soil animals. Bunge ('88, p. 566) found that 

 earthworms were able to survive one day in an oxygen- free liquid. 



