THE ANTS, BEES, AND WASPS 



81 



The agricultural ant (Myrmi'ca molefac'iens), of the same 

 region, clears large spaces, often several feet in diameter, 

 cutting down all vegetation growing thereon, and rears a 

 grain-bearing grass, storing its seeds in subterranean chambers. 

 Several kinds of ants have the habit of attacking other kinds 

 and carrying off their pupse. In one (Formi'ca sanguin'ea), a 

 small reddish species, the habit has become firmly fixed, and 

 periodical raids are made upon a larger black species, which 

 are afterwards raised in the nests of their captors. One ant 

 of a slave-making tendency, found in Europe (Polyer'gus 

 rufes'cens), has carried the habit so far that it has lost the 

 power of feeding and taking care of itself, depending entirely 

 on the exertions of its servants. The wars of ants have been 

 known for a long time, and many accounts are extant of the 

 fierceness of the struggle between opposing armies. 



Gall-Flies and Ichneumon-Flies. The gall-flies form many 

 of the swellings on plants, known as galls. A common gall- 

 fly of the oak 

 (Amphib'olips) 

 is shown in Fig. 

 48. The gall is 

 caused by the 

 female laying 

 an egg in the 

 leaf- tissue, 

 which swells up 

 when the larva 

 hatches, owing, 



perhaps, to the 



FIG. 48. Gall-Fly . Natural size 

 presence of some 



irritating substance. The young feed on the material of the 

 gall until they are ready to go into the pupal stage. Many 

 of these galls harbor also guest gall-flies, living with the 

 others as commensals. 



