138 ROMANCE OF THE INSECT WORLD CHAP. 



" pavement " again unencumbered until autumn, when 

 the same favoured plant once more presents itself. It 

 has been urged that the needle grass is deliberately 

 sown by the ants on the cleared ground in summer, 

 and is cultivated with the intention of reaping a crop 

 from it in the following spring. It seems hardly 

 possible to credit them with such wisdom. Nor on 

 the other hand, as the opponents of this theory believe, 

 is it likely that they are overtaken by the autumn 

 " rice," and are unable to prevent it, since surely the 

 power which enabled them to eradicate all usurping 

 winter growth from their domain in spring, would 

 admit of them keeping it clear. Besides, the exclusive 

 occupation of the disk by this grass, so long as the 

 ants are up and about, counts in favour of voluntary 

 action on the part of the insects. Probably the 

 Aristida is seeded yearly in a natural way by drop- 

 pings from the plant, or from seeds dropped or cast 

 forth by the ants ; and the ants find it to their ad- 

 vantage to permit and foster the ensuing growth, 

 because of greater convenience of harvesting the seed, 

 while, farmer-like, they expel all other vegetation from 

 their precincts. 



In some instances the central clear space 

 is occupied by a low mound, in shape some- 

 what like a volcanic cone with a crater-like 

 depression- at the summit. A distinct flat bare 

 belt or zone may exist between the mound and the 

 margin of the nest, of no great width ; or the grass of 

 the surrounding prairie may grow up to the cone's 

 base. The material composing the mounds is a light 

 sandy soil. Other nests have gravel disks. Round 



