962 AN INTRODUCTION TO ENTOMOLOGY 



their surfaces in a kind of feverish excitement. This shampooing has 

 a two-fold object: to obtain the oleaginous salivary secretion with 

 which the Myrmicas cover their bodies when they clean one another, 

 and to induce these ants to regurgitate the liquid food stored in 

 their crops." 



The fungus-growing ants.- — Among the many remarkable examples 

 of insect behavior none is more marvellous than the habits of the 

 fungus-growing ants, although analogous habits are exhibited by 

 certain termites and by the ambrosia beetles, discussed in earlier 

 chapters of this book. 



The fungus-growing ants constitute one of the tribes, the Attii, 

 of the Myrmicin^, of which about loo species, subspecies, and 

 varieties have been described. They are confined almost exclusively 

 to tropical and subtropical America; but one species is found as' 

 far north as New Jersey. Many accounts have been published re- 

 garding these insects, which have been commonly known as the leaf- 

 cutting ants or the parasol ants. These names were suggested by 

 the fact that these ants cut pieces from the leaves of trees and carry 

 them, like parasols, into their nests. 



The use that the ants make of the leaves that they carry into their 

 nests was long a mysterv\ But it is now known that the leaves are 

 used as a culture medium upon which they cultivate a fungus, which 

 they eat and feed to their lar^^as, and which is their only food. 



Professor Wheeler ('07 b) has published a monograph of the 

 fungus-growing ants of North America in which is given a resume of 

 the writings of previous students of the Attii; and a chapter is de- 

 voted to these insects in his volume on "Ants" ('10). 



Subfamily DOLICHODERIN^ 



In this subfamily, as in the following one, the pedicel of the ab- 

 domen consists of a single segment and there is no constriction between 

 the first and second segments of the gaster ; but these ants can be dis- 

 tinguished from the Formicinse by the fact that the anal orifice is in 

 the form of a slit. These ants, also, often possess in addition to the 

 poison glands, anal glands which excrete a foul smelling, sticky fluid, 

 which is used as a means of defense in their combats with other ants. 



Only about a dozen species have been described from our fauna 

 and most of these are southern. Certain tropical species build carton 

 nests attached to trees and some of our species make carton nests 

 under stones. The members of this subfamily are especially fond of 

 honey-dew and attend aphids and coccids to secure it. Some of the 

 species, "establish their nests on or near the nests of larger ants and 

 either feed on the refuse food or waylay the workers when they return 

 home and compel them to give up their booty" (Wheeler). The 

 most important species of the subfamily in our fauna is the following. 



The Argentine ant, Iridomyrmex humilis. — This is an introduced 

 species, which has become an exceedingly serious pest in the Gulf 

 States and in Southern California. Its injuries are of two kinds: 



