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 (Z7phia 
vulgaris) of the May-beetle larva 
(Figs. 296-97) occurs commonly. 
Several species of aphids (Figs. 
298-300) occur, especially on the 
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 repreduce rapidly, the young being 
born in rapid succession at a very ad- 
vanced state of development. They 
begin sucking the juices of the plant 
atonce. Several small parasitic 
hymenoptera (braconids) (Fig. 
299) lay their eggs in the bodies 
of the aphids. These finally kill 
the aphids, whose bodies with 
Fic. 298.—A viviparous grain louse (Macrosiphum granaria Kirby) with her 
newly born young on a barley leaf (after Washburn, Bull. 108, M inn. Agr. Exp. Sta., 
Fig. 2, p. 262). 
‘ 
