in the morning and the first to leave them in tlie eve- 

 ning. I'.xperiments sliow that they of all insects in 

 this habitat are the most tolerant of the high temper- 

 atures. Animals living here must either be physio- 

 logically tolerant of extreme heat or possess behavior 

 jvitterns that enable them to avoid it. 



Grassh 



uppers and other Orthitptc 



There have been detailed studies of a few spe- 

 cial groups of animals occupying the Lake Michigan 

 sand dunes. Three species of wood roach, 2 species 

 of walking-stick, 20 species of short-horned grass- 

 hopper, 13 species of long-horned grasshopper, and 

 6 species of field cricket occur in various stages 

 of the sand sere in the Chicago area (Strohecker 

 1^37). A breakdown of this list shows that 7 species, 

 all short-horned grasshoppers, occur in the grass and 

 Cottonwood stages : of these, one species is not found 

 in the pine stage, and the other 6 species disappear 

 by the time the black oak stage is reached. Eight new 

 species of orthopterans, including 4 short-horned 

 grasshoppers, enter the sere at the pine stage, but 

 only 5 species persist into the black oak stage. Alto- 

 gether there are 23 species of orthopterans listed for 

 the black oak forest, an increase of 18 new species. 

 There are only 25 species of orthopterans listed for 

 the climax, but this includes 4 species of camel 

 crickets which for the first time can find their proper 

 niches under logs, and a katydid that appears in the 

 trees. The greatest change in species composition 

 within the sere occurs at the black oak stage upon 

 the disappearance of 67 per cent of the species present 

 in the earlier stages and the appearance of 78 per 

 cent of the species as new forms. Of that 78 per cent, 

 61 per cent persist through all later stages. The 

 change in species composition at this stage can be 

 correlated with the development of a canopy of foliage 

 and the resulting reduction in light intensity and 

 soil temperatures. 



The community or niche restriction of the 

 short-horned grasshoppers appears to be deter- 

 mined either by soil conditions or by the vegetation 

 (Tsely 1938a). Before short-horned grasshoppers lay 

 their eggs in the ground, the female tests the soil 

 with her ovipositors until she finds soil of proper 

 conditions. Experimental studies show that in cer- 

 tain cases soil texture is the critical factor in the 

 choice of the egg-laying site, while in other cases soil 

 structure or degree of compaction is most important. 

 Soil conditions appear particularly important for the 

 sub-family of band-winged grasshoppers : for other 

 groups, vegetation is of greater significance. 



In an experimental study of how an available 

 choice between foods may affect distribution (Isely 

 1938a), one-half of 40 species of short-horned grass- 



20 25 30 35 40 45 50 55 

 TEMPERATURE, °C 



rature gradient on a sand dune, on a rainy 

 nny day (after Chapman e/ o/. 1925). 



hoppers showed a feeding preference for grasses and 

 one-half for broad-leaved herbs. The latter group in- 

 cluded the spur-throated grasshoppers. Four species 

 were restricted to feeding on a single plant species ; 

 30 species confined themselves to a few plant species 

 only, and usually of a single plant family at that ; 

 only 2 species fed on a wide variety of plants. In 

 several instances grasshoppers starved in cages, when 

 there was an abundance of fresh plant materials pres- 

 ent that were palatable for other species, because their 

 own preferred food species were absent. 



All five species of false katydids studied in Texas 

 (Isely 1941) confined their choice of food to related 

 species of broad-leaved herbs or forbs, refusing 

 grasses ; adults showed a marked preference for the 

 flower parts and tender fruit pods. Two species of 

 shield-backed grasshoppers were wholly carnivorous. 

 The flower-feeding false katydids disappeared from 

 the prairie in late spring and early summer as the 

 flowering plants passed their peak, but the insect- 

 feeding grasshoppers persisted to the end of July or 

 initil temperatures became too high for their comfort. 



Anis 



.•\nts cannot get established on the beach be- 

 cause of its unstable character and are scarce even 

 in the grass and cottonwood stages because of the 

 shifting character of the dunes (Talbot 1934). Spe- 

 cies found are crater-formers Lasius niger neoniger 

 and Pheidolc bicarinata. and two species of Cainpo- 

 notus that find protection under the occasional log 



Rock, sand, and clay 



07 



