1907.] Wheeler, Fungus-growing Ants of North America. 751 



Pis. LI-LIII, Figs. 30-46. The mycelium in flourishing colonies has a 

 bluish tint, somewhat like that of Pcnicillium glaucum. The hyphae measure 

 .78 p. in diameter. The gongylidia are subspherical or pear-shaped, and 

 average 4.5 jjl in length and 3.6 jj. in breadth, and are grouped in compact 

 clusters or bromatia averaging .4-.5 mm. in diameter. 



In Texas the most favorable time to study the nests of T. ohscurior is 

 during the month of April. Then the ants are actively enlarging and deepen- 

 ing their nests and bringing in supplies for their gardens. While excavating 

 they advance in a small phalanx up the inclined entrance gallery, each laden 

 with a cuboidal sand pellet about 2 mm. in diameter, walk slowly to the 

 sand pile, deposit their burdens and then return for others. The dealated 

 females, of which there may be as many as four or five in a nest, toil in the 



Fig. 21. Brood of Atta {Trachymyrmex) obscurior. About twice natural size. Three 

 packets of eggs are shown enveloped in fungus mycelium. (Photograph by Mr. A. Beutenmuller.) 



phalanx like the workers. At the slightest alarm the ants immediately 

 retreat into the nest and usually a single worker takes up her position in the 

 entrance and holding a sand-pellet in her jaws, waits patiently till all danger 

 has passed, before venturing forth and leading the troop of her sand-laden 

 sisters. When foraging the ants go out singly and in various directions, 

 pick up what they can find and return with it to the nest, moving slowly 

 and sedately over the sand. The dealated females may also be seen in the 

 act of carrying caterpillar droppings and leaves to the nest. If rudely 

 touched with the finger or a stick, the in.sect drops her burden, curls herself 

 up, folds her legs and antcnnse and "feigns death." At such times her 

 rough yellowish brown body is almost indistinguishable from the sand on 

 which she lies. When the nest is ruthlessly torn open, the ants, especially 



