BIOLOGICAL PAPERS. 



165 



sizes and heights, depending on the age, size and location of the 

 colony. Of those measured in the grass on the prairies, the prevail- 

 ing height was about nine inches, while those located in an alfalfa- 

 field, in Ellis county, Kansas (see plate XXIV), were about four 

 inches in height. The mound is made very prominent by the cleared 

 space, by which it is surrounded. This clearing is usually circular 

 in form, although it may be somewhat elliptical. The mound is 

 usually located in the center of the clearing, which is always abso- 

 lutely void of vegetation. The size of this clearing depends on the 

 size of the mound and the nature of the surrounding vegetation. 

 Those found in the buffalo-grass are much smaller than those in a 

 cultivated field. A large nest may be found with a comparatively 

 small clearing; however, this is not common. The clearings sur- 

 rounding the nests located in the buffalo-grass averaged nine feet ; 

 those in the Russian thistles, eleven feet ; those in an alfalfa-field, 

 thirteen to fourteen feet. This clearing is usually smooth and level. 

 These ants, like most mound-building specimens of ants, have a dis- 

 like to the presence of vegetation in the immediate vicinity of their 

 mound. 



EXTERIOR MEASUREMENTS OF NEST. IN INCHES. 



The clearing away of the vegetation is accomplished by the work- 

 ers cutting it away wnth their mandibles, which are well adapted for 

 the purpose of such work. We may assume several reasons why the 

 ants wish to have a cleared space. The plants too near the nest 

 would be a hindrance to their going and coming. They would afford 

 a shelter or hiding-place for any enemy or intruder. Vegetation 

 would endanger the nest by the retention of moisture after a rain. 

 T he nest would be seriously damaged by the roots of any plants grow- 



