INTERRELATIONS OF INSECTS 



339 



FIG. 285. 



the sake of which the ants carry on their complex oper- 

 ations consists of the knobbed ends of fungus threads 

 (Fig. 285), and these bodies, rich in fluid, form the most 

 important, if not the sole food of the leaf-cutting ants. By 

 assiduously weeding out all foreign organisms the ants ob- 

 tain a pure culture of the fungus, and by pruning the fungus 

 they keep it in the vegeta- 

 tive condition and prevent 

 its fructification ; under 

 exceptional circumstances, 

 however, the fungus devel- 

 ops aerial organs of fructi- 

 fication of the agaricine 

 type, but this species (Ro- 

 zites gongylophora ) has 

 never been found outside 

 of ants' nests. The pecu- 

 liar clubbed threads were 

 produced by Moller in arti- 

 ficial cultures and are not 

 spores, but products of cul- 

 tivation. Other ants are known to cultivate other kinds of 

 fungi for similar purposes. 



McCook has found a leaf-cutting ant (Atta fervens) in 

 Texas, and mentions that it cuts circular pieces out of leaves 

 of chiefly the live-oak, these being dropped to the ground and 

 taken to the nest by another set of workers. He records an 

 underground tunnel of Atta fervens which extended 448 feet 

 from the nest and then opened into a path 185 feet in length; 

 the tunnel was 18 inches below the surface on an average, 

 though occasionally as deep as 6 feet, and the entire route led 

 with remarkable precision to a tree which was being defoliated. 



The same observer has given also a brief account of a leaf- 

 cutting ant that lives in New Jersey. This species (Atta sep- 

 tentrionalis) cuts the needle-like leaves of seedling pines into 

 little pieces, which are carried to the nest. Two columns of 



Fungus clumps (Rosites gongylophora) 

 cultivated by ants of the genus Atta. 

 Greatly magnified. After MOLLER. 



