1907.] Wheeler, Fungus-growing Ants of North Ainerica. 671 



Genus Apterostigma Mayr. 



A. pilosuni^lAyr; scuicIIareFovel; moelleri Forel; wasmanniFovel; urichi 

 Forel; mayri Forel; colkirc Emery; rohustum Emery. 



The various subgenera included under Atta sensu lato will probably be 

 raised eventually to generic rank. The subgenus Atta comprises the leaf- 

 cutting or parasol ants, the largest and most powerful species of the tribe, 

 living in great colonies and inhabiting the territory between 30° north and 

 30° south of the equator. The workers are highly polymorphic and much 

 smaller than the riiales and females. The colonies of the species of MoeUerius 

 and Acromyrmex are much less populous, and the workers, though variable 

 in size, do not exhibit such marked polymorphism as those of Atta s. str. 

 In Trachijmijrmex and the remaining subgenera the workers are mono- 

 morphic and but little smaller than the males and females, and the colonies 

 are even feebler than those of Acromyrmex. Mycetosoritis and Mycocepurus 

 are in certain respects transitional to the genera Cyphomyrmex and Myr- 

 micocrypta, and species of the last show affinities with Sericomyrmex. Apte- 

 rostigma is very aberrant, resembling in form certain ]Myrmicines of the 

 subgenera Apha^nogaster and Ischnomyrmex. The workers of Atta are 

 covered with stiff, erect or suberect, hooked or curved hairs, and the sur- 

 face of the body is tuberculate or spinose. In Cyphomyrmex the body is 

 smoother and covered with short, appressed, scale-like hairs. In Serico- 

 myrmex and Apterostigma the hairs are soft, fiexuous and very abundant. 

 With few exceptions all the Attii have the surface of the body opaque and of 

 a ferruginous, brown or blackish color. All the species, moreover, though 

 very powerful and able to make surprisingly extensive excavations in the 

 soil, are very slow and stolid in their movements. The sting of the workers 

 is vestigial, but in the larger species the sharp jaws may be used as most 

 efficient organs of defence. The smaller species are extremely timid and 

 when roughly handled "feign death" like Curculionid beetles. In all the 

 species the hard, rough or spinose integument must afford efficient protection 

 from alien ants and other enemies. 



Owing to the labors of Forel, Emery and INIayr our knowledge of the 

 taxonomy of the Attii is probably as satisfactory as that of any other groups 

 of exotic ants. As much cannot, however, be said of our knowledge of the 

 habits. Since all the Attii live in intimate symbiosis with fungi, a complete 

 study of the habits of these insects requires the diligent cooperation of the 

 entomologist and botanist. Hitherto the botanists, notably Alfred Moeller 

 and Jakob Huber, have contributed the most accurate observations. As 

 neither the botanists nor the entomologists of North America have shown 

 any very serious interest in the Attii, I need not apologize for publishing the 



