290 



PRAIRIE COMMUNITIES 



usual leader of the clan. On the great plains these united 

 and formed the larger herds of 20,000 to 4,000,000 or more, 

 which have been described by travelers. The males aided 

 in defending the young. The cowbird is said to have fol- 

 lowed the herds constantly. 



b) Field stratum. — The lepidopterous larvae are similar 

 to those of the low prairie, but much less numer- 

 ous. The hymenoptera are represented by Bom- 

 bus separatus, and many of those recorded on the 

 low prairie. The adult of the parasite (Tiphia 

 vulgaris) of the May-beetle larva 

 (Figs. 296-97) occurs commonly. 

 Several species of aphids (Figs. 

 298-300) occur, especially on the 



A 



milkweeds and thistles. 

 These are commonly at- 

 tended by ants, which 

 stroke them and secure the honey dew from 

 the posterior ends of their alimentary canals. 

 The aphids reproduce rapidly, the young being 

 born in rapid succession at a very ad- 

 vanced state of development. They 

 \ begin sucking the juices of the plant 

 "\ at once. Several small parasitic 



\ hymenoptera (braconids) (Fig. 



\ 299) lay their eggs in the be dies 



of the aphids. These finally kill 

 - A the aphids, whose bodies with 



Fig. 298. — A viviparous grain louse (Macrosiphum granaria Kirby) with her 

 newly born young on a barley leaf (after Washburn, Bull. 108, Minn. Agr. Exp. Sta., 

 Fig. 2, p. 262). 



X 



