THE MOUND OF POGONOMVRMEX BADIUS LATRL. 163 



from the nest the pebbles that the ants working from within the 

 nest had carried inward from the obstruction. 



Whether a nest contains several openings or only one, early in 

 the morning and at night the openings are found to be closed. 

 In the spring and early summer, I have often found all of the 

 nest openings closed as late as 7:50 A. M. Careful observations, 

 extending over a period of five months, demonstrated that the 

 nest opening or openings are regularly closed, by the ants, at the 

 close of day. The time required to complete the closing and the 

 number of ants employed varies in different nests and in the same 

 nest at different times ; but the method in all cases is so similar 

 that the following description of the behavior of the ants on one 

 occasion will serve as a type of all. 



It was eighteen minutes to seven, July 20, 1908, and darkness 

 was fast approaching. Four workers were busy covering the 

 nest opening with plant debris, sand and pebbles. Part of the 

 time they would stand balanced upon the two posterior pairs of 

 legs, with their heads turned away from the nest, and kick the 

 sand backwards with their fore feet ; and part of the time they 

 would carry coarser materials and place them upon the nest. 

 By twenty-three minutes after seven, the opening was almost 

 closed and the ants passed inside. In a few minutes, two workers 

 returned to the outside and continued the closing of the opening. 

 Soon they were joined by a third worker. By forty minutes after 

 seven the opening was closed ; then the three workers wedged 

 themselves inward through the closed entrance. Soon a worker 

 returned to the outside and added more material to the pile over 

 the nest opening. Then it forced its way into the nest. This 

 behavior was repeated several times. The nest was finally closed 

 from within. By eight o'clock everything was quiet. 



On one occasion, I noticed this ant make use of this hole- 

 closing instinct to rid itself of the encroachments of another ant. 

 A species of Atta had constructed a burrow within the confines 

 of a mound of a colony of Pogononiyrmex badiits. When I first 

 discovered these conditions, a single worker of the latter species 

 was busy covering the opening of the burrow of Atta with sand. 

 The sand was driven into the opening by the ant standing on its 

 four hind legs and kicking the sand backward with its fore feet. 



