THE FUNGUS-GROWING ANTS. 337 



a more bluish tint and the substratum is coarser and less flocculent and 

 often consists of caterpillar droppings. 



4. Mivllcriits. Our only species is M. vcrsicolor (Fig. 197), a 

 Mexican ant which enters the extreme southern portion of Texas and 

 Arizona. It constructs elegant craters 10-30 cm. in diameter in sandy 

 depressions in the deserts (Fig. 198). The subterranean portion of 

 the nest has not been satisfactorily explored, but probably consists of 

 a single large chamber with a single fungus garden on its floor, as 

 in the South American species of Ma:llcrius and the closely allied 

 Acroin\rmex. M. versicolor, unlike the ants of the preceding groups, 

 is a true leaf-cutter, /. e., it defoliates shrubs and trees like the species 

 of Atta s. str. and does not collect the substances for the substratum 

 of its gardens from the surface of the ground about the nest. 



5. Atia s. str. A. tc.vana ( Figs. 199 and 200), the leaf-cutting 

 ant, our only species of this subgenus, occurs in loamy or sandy soil 

 in central Texas. It is the largest and most formidable of our species 

 and often does considerable injury to cultivated plants along the Brazos 

 and Guadeloupe Rivers. Its habits are similar to those of the South 

 and Central American A. ccphalotes and sc.rdcns. Externally the nest 

 appears as a large, flat mound, often covering an area of more than 

 100 sq. m., and made up of a number of more or less fused craters, 

 10-100 cm. in diameter, with large openings (3-6 cm.) leading into 

 galleries of the same diameter. These galleries often extend to a 

 depth of 2-5 m., where they enter chambers sometimes 50-100 cm. long 

 and 30 cm. broad and high, with flattened floors and arched ceilings 

 (Fig. 202). On the floor of each chamber lies a large garden, made of 

 triturated leaves, built up in the form of an irregular comb or flattened 

 sponge, covered with a white mycelium and studded with the usual 

 bromatia, or food-bodies (Fig. 203). A. te.vana is the only one of 

 our species which has highly polymorphic workers. The minimse 

 always remain in the gardens where they carefully weed the hyphae 

 and prevent the growth of any alien fungi that may be introduced by 

 the foraging workers ; the mediae cut, carry in and triturate the leaves 

 and build up the garden ; while the maximae, or soldiers, guard the 

 nest. 



The foregoing series of forms together witn others occurring only 

 in tropical America, show a perceptible advance in the fungus-growing 

 habit within the Attiine tribe. The lower genera Cyplioinynnc.v, and 

 probably also Mynnicocrypta, make small, crude nests, with irregular, 

 sessile gardens of insect excrement. Apterostigma, Scricomyruic.r. 

 ]\I \cetosoritis and Trachymyrtnex all excavate more regular nests and 

 construct pendent gardens of insect excrement and vegetable debris. 



23 



