THE HARVESTING ANTS. 



291 



crushed or broken seeds. In my artificial nests these pieces were 

 coated with saliva by the workers before being administered to the 

 brood, a precaution which may insure the conversion of the starch into 

 sugar and facilitate its assimilation by the larvae. 



The Occident harvester (P. occidentalis) which ranges over the 

 Great Plains from Montc.na to northern Texas, New Mexico and Ari- 

 zona, rarely descending below 5,000 feet and thriving best at an altitude 

 of 6,000 to 8,000 feet, has been studied by Leidy ( 18/7 ) and McCook 

 (1882) and more recently by Headlee and Dean (1908) and myself. 



FIG. 165. Diagrams of three stages in the development of the modified masonry 

 dome of Pogonomyrmex occidentalis. (Original.) A, Small mound of earth thrown 

 up by queen when starting her formicary ; .r, entrance, z, first chamber ; A', same 

 nest in section : B, crater nest (second year) formed by incipient colony ; B' section 

 of same ; C, mound, or dome of adult colony ; C' section of same showing galleries 

 and chambers. 



It is a smaller ant than P. barbatus and much more precise and uniform 

 in its nesting habits. Its constructions are, in fact, the most elegant 

 and extensive of any of the known species of the genus. As in the 

 case of barbatus, the edge of the carefully cleared disk on which the 

 fine gravel cone rests is sometimes surrounded by a circle of grass or 

 other plants which grow from the refuse heap (Fig. 163). P. occi- 

 dentalis is not in the habit of foraging in files, so that no paths radiate 

 from the cleared disk. This absence of paths is attributed by McCook 

 to the sparse and tufted character of the vegetation of the Great 

 Plains, which makes beaten roads unnecessary. 



During July, 1903, I witnessed the nuptial flight of this insect near 



