1932] The Thatching Ant, Formica obscuripes 31 
acid is required for the destruction of the plant is ques- 
tionable but it is doubtful whether elimination could be 
completely accomplished without it. After the plant has 
been killed it dries and the branches are broken off and 
disseminated by the wind. This operation takes place very 
slowly, it requiring sometimes as long as three months 
for the plant to be entirely eliminated. One can often 
observe mounds in which the stems have been broken off 
flush with the apex of the mound. In such cases the oper- 
ation of destruction is incomplete for eventually the entire 
Fig. 1. Typical mound of Formica obscuripes composed of wheat 
straw. Twin Falls, Idaho. 
stem is removed. When the operation is complete the cen- 
ter of the mound will be found to possess a large longitud- 
inal gallery, apparently the main entrance to the interior 
of the mound. 
The main brood chambers are located approximately 
three feet lower than the base of the mound proper, but 
auxilliary chambers are scattered throughout the re- 
mainder of the nest where the brood may be moved upon 
