77 



of small nematodes, often very abundant in grasshoppers and beetles; 

 nematodes, trematodes, and cestodes in vertebrate animals. Com- 

 mon ectoparasites to be looked for are mites, Mallophaga, and fleas. 

 Many parasitic insects other than those listed above are to be ex- 

 pected, particularly among the Bojiibyliidac and Tachinidae in Dip- 

 tcra, and the division Parasitica in Hynicnoptcra. 



The free-living stages of parasites are represented in all the 

 strata of the bunch-grass association. 



There is often little distinction, from the ecological point of view, 

 between parasites and such predaceous animals as are of more or 

 less selective food-habits. It is sometimes difficult to decide whether 

 an animal is parasitic or predaceous. The positions of the two groups 

 in the association are essentially the same. 



SCAVENGERS OF THE BUNCH-GRASS 



The scavengers are of different types, according to the character 

 of their food. Omnivorous animals are scavengers in part. Others 

 may eat dead wood, decaying herbaceous material, carrion, animal 

 excrement, or the organic matter in the soil. Certain animals de- 

 pend on the presence of humus., though it is not known whether their 

 food is dead organic material, or small living organisms of the soil. 

 However, as humus is not abundant in the Illinois River sand, ani- 

 mals depending on its presence are accidental, and the question need 

 not be entered upon here. Wood-feeders also are not typical mem- 

 bers of prairie associations. 



Omnivorous animals 



CcuthopJiilus sp. Formica paUide-fulva schaufitssi 



Grylliis pcniisylz'aiiicits Monouoriioii jiiinntHiJi 



Humus-feeders 

 Diplocardia sp. Bntoiiiobrya sp. 



Parajuhis sp. 



Wood- feeders 



Tcrnics flaripes Ischnoptera sp. 



Carrion-feeders 



Necrophoriis jiiargijiatits Dermestes znilpinus 



Silpha inacqnalis Trox scabrosits 



StapJiyliuidac Sarcophagidac 

 Dcriiicstcs caiiijius 



