130 



the forest glades; and many ground-inhabiting Orthoptera in the for- 

 est oviposit in the soil as do their congeners on the prairie. On Isle 

 Royale, Michigan, I found that the carabid beetles which lived in the 

 openings were likely to extend into the coniferous forest in the humus 

 layer, which corresponds to this habitat in the open, and this is prob- 

 ably true to some degree in Illinois forests. 



In the denser forest, in marked contrast with the prairie, there is 

 generally a large amount of litter on the forest floor. The prairie soils 

 are dark, but the surface contains a relatively smaller amount of or- 

 ganic materials comparable to forest litter. In the forest, however, 

 though the sub-surface soil is relatively light in color, the surface con- 

 tains much fresh and partially decayed organic debris. 



McAfee ('07) has made a careful count of all the invertebrates 

 found upon an area of four square feet of the forest floor, at or near 

 the surface. This is the only quantitative study made of our forest 

 soil animals known to me. His observations were made during the 

 hibernating season. 



Representative plant-feeding ground animals are the two cicadas 

 linnei and septendecim, which suck sap from the roots of trees. Their 

 underground enemies seem to be largely mites. The arboreal habit of 

 the adults subjects them to many enemies. The periodical cicada, as 

 the result of subterranean life, in the moist soil, displays little resist- 

 ance to drying, and when exposed to the air soon shrivels, as shown 

 by Marlatt ('07, p. 123). When conditions in the soil are unfavorable 

 (1. c, p. 96) as the period of emergence approaches, some individuals 

 respond by building a mud tube, similar to the crawfish chimneys, 

 which are closed with a plug of mud. That saturated ground seems 

 to be an unfavorable condition at this stage suggests that resistance 

 to the lack of oxygen decreases as the insect matures. Most of the 

 nymphs of this species live within less than two feet of the surface, 

 though some rather inconclusive observations indicate that the 

 nymphs have a wonderful resistance to submergence, as is shown 

 by the following quotation from Marlatt ('07, p. 125) : "A 

 curious feature in connection with the underground life of 

 this insect is the apparent ability to survive without injury in 

 soib which may have been flooded for a considerable period. Doctor 

 Smith records a case of this kind where a gentleman in Louisiana in 

 January, 18 18, built a milldam, thus overflowing some land. In March 

 of the following year the water was drawn off and 'in removing a hard 

 bed of pipe clay that had been covered with water all of this time some 

 6 feet deep the locusts were found in a fine healthy state, ready to make 

 their appearance above ground, that being the regular year of their 

 appearance.' Another case almost exactly similar is reported by Mr. 



