49 



Bpeolus concolor on the flowers of Lepachys indicates the attractive 

 power of this plant. The coarser plants furnish support for the webs 

 of Argiope; the flowers serve as drinking cups in which Phymata lies 

 in ambush ; and the varied vegetation affords food for the numerous 

 Orthoptera. The proximity of ground-water accounts for the pres- 

 ence of Cambarus, and an adjacent corn field explains the presence 

 of Diabrotica. A robber-fly (Asilidcs) was seen but not captured. It is 

 interesting to see Melissodes obliqua as it hurries round and round the 

 heads of cone-flowers and sweeps up the great masses of yellow pollen. 

 The hind pair of legs, when loaded with pollen, have nearly the bulk 

 6f the abdomen. Robertson ('94; 468) says that this is the most 

 abundant visitor to the cone-flower, and more abundant on this flower 

 than on any other. 



It is probable that the conditions within this* habitat were suitable' 

 for the breeding of most of the species listed. Buaresta cequalis has 

 been bred from the seed pods of the cocklebur (Xanthium) and prob- 

 ably came from the adjacent corn field. It is most likely on flowers 

 that the strepsipterid parasitic insects find many of their hosts (Pierce 

 '09 b : 1 16). These insects are found on the following prairie insects : 

 Polistes, Odynerus, Chlorion ichneumoneum, C. pennsylvanicum, and 

 C. atratum. Robertson ('10) records many important observations on 

 the hosts of Illinois Strepsiptera. 



5. Colony of Blue Stem (Andropogon) and Drop-seed (Sporobolus), 

 bordered by Szvamp Milkweed, Station I, g* 



This colony formed the extreme northern part of the prairie area 

 examined along the "Clover Leaf" track. It extended along the track 

 for a distance of about 200 feet. The area is level black soil prairie. 

 Its general appearance and location are indicated in Figure 2, Plate 

 II, and in Figure 2, Plate III, photographs taken at the time of our 

 study, and in Figure 2, Plate IV, a photograph taken by T. L. Hankin- 

 son April 23, 191 1. This latter view clearly shows the character of the 

 drainage during the spring wet season. During the late summer, the 

 dry season, the ditch along the railway track concentrates the drainage 

 so that a colony of swamp milkweed (Asclepias incarnata) and small 

 willows flourish in it. Upon the well-drained part of this area there is 

 a rather rich growth of Andropogon furcatus, A. virginicus, and 

 Sporobolus cryptandrus, and many plants of the dogbane Apocynum 

 medium and a few plants of Asclepias sullivantii. This was the larg- 

 est and best colony of the upland prairie grasses seen along the Clover 

 Leaf tracks; and yet when it is compared with the patches of such 

 *No collections were made at Station I, /. 



