MUTUAL AID AND COMMUNAL LIFE AMONG ANIMALS 375 



have the careful observations of Professor Forbes to rely on. 

 In the Mississippi Valley, this aphid deposits in autumn its 

 eggs in the ground in corn fields, often in the galleries of the 

 little brown ant. The following spring before the corn is 

 planted, these eggs hatch. Now, the little brown ant is es- 

 pecially fond of the honey dew secreted by the corn root lice. 

 So when the latter hatch in the spring, before there are corn 

 roots for them to feed on, the ants carefully place them on 

 the roots of certain kinds of grass and knotweed (Setaria, 

 Polygonum), and there protect them until the corn germinates. 

 They are then removed to the roots of the corn. It is prob- 

 able that the ants even collect the eggs of the aphids in the 

 autumn and carry them into their nests for protection and care. 



The studies of Wheeler and others have revealed some 

 interesting cases of the living together of different species of 

 ants. In some cases one of the ant species may be living almost 

 wholly at the expense of the other species, as does the little 

 yellow thief-ant, Solenopsis molesta. Although this ant some- 

 times lives in independent nests, more often it is to be found 

 living in association with some large ant species it consorts 

 with many different hosts feeding almost exclusively on the 

 live larvse and pupae of the host. The thief -ant is so small 

 and obscurely colored that it seems to live in the nests of its 

 host practically unperceived. The Solenopsis nest may be 

 found by the side of the host nest, around it, or partly in it, 

 the tiny Solenopsis galleries ramifying through the nest mass 

 of the host, and often opening boldly into these large galleries. 

 Through their narrower passages, too narrow to be traversed 

 by the hosts, the tiny thief-ants thread their way through the 

 host nest in their burglarious excursions (Fig. 245). 



But there are numerous cases of a less one-sided advantage 

 in the association of different species. As an example the 

 conditions exhibited by the red-brown ant, Myrmica brevi- 

 nodes and the smaller Leptothorax emersoni (conditions made 

 known by Wheeler's careful observations) may be briefly 

 described (Fig. 246). The little Leptothorax ants live in the 

 Myrmica nests, building one or more chambers with entrances 

 from the Myrmica galleries, so narrow that the large Myrmi- 

 cas cannot get through them. When needing food the Lepto- 

 thorax workers come into the Myrmica galleries and chambers 

 and, climbing on the backs of the Myrmica workers, proceed 



