1907,] Wheeler, Fungus-growing Ants of North America. 753 



When its nest is disturbed, T. septentrionalis, like other Attii is very 

 careful to rescue portions of its fungus gardens as well as its brood. A 

 number of colonies, whose nests I had excavated in the post-oak woods at 

 Montopolis, were found a few days later to have made new nests a few feet 

 from the old sites and to have carried with them such fragments of their 

 gardens as they could rescue. They had suspended these to the rootlets in 

 one or two chambers which they had succeeded in excavating in the mean- 

 time, and were busy carrying in caterpillar excrement and withered oak 

 catkins. 



During the spring and autumn T. septentrionalis may be found abroad 

 at all hours of the day, but with the growing heat of the summer it becomes 

 increasingly crepuscular and nocturnal. And as soon as the dry Aveather 

 sets in, it greatly contracts or completely closes with dead leaves and twigs 

 the orifice of its nest to reduce or prevent the evaporation of the moisture 

 from the chambers. The sandpile subsides under the influence of the ele- 

 ments till the nest becomes barely distinguishable from the surrounding 

 leaf -strewn surface (Fig. 22). It is then almost impossible to find the 

 nests even in localities where previous exploration has shown them to be 

 very numerous. The ants no longer venture forth but spend all their time 

 weeding and rearranging their gardens in the moist subterranean chambers. 

 Immediately after the first warm rain, however, the nests are reopened, ex- 

 cavations and repairs to the chambers are renewed, the exhausted portions 

 of the gardens are ejected and the ants sally forth in quest of fresh supplies. 



4. Atta (Trachymyrmex) turrifex Wheeler. 



As this species is even more timid and retiring than T. septentrionalis, 

 it was some time before I learned to find its colonies and gained an acquaint- 

 ance with its habits. Its geographical range covers the dry deserts of Trans 

 Pecos Texas, and slightly overlaps the range of septentrionalis along the 

 escarpment of the Edwards Plateau in the central portion of the state. 

 That it is a more adaptable ant than its eastern and northern congener, is 

 shown by its occurrence in the following diverse stations : 



1. In the treeless deserts at Del Rio, Langtry, ]Marfa, Alpine and Ft. 

 Stockton, in dry stony soil fully exposed to the glare of the sun. In these 

 localities the colonies are widely scattered. 



2. In the clayey soil of the post-oak woods and "cedar-brakes" (Juni- 

 perus sabinoides) near Austin (Fig. 23), along the Perdenales River, and at 

 Marble Falls. Here the colonies are often numerous and close together. 



3. In the pure sand of open fields at Montopolis on the Colorado River. 

 In this locality the colonies are infrequent and mingled with those of sep- 



Sept., 1907.] 4S 



