206 HEMIPTERA. 



To increase and multiply is their principal business in this 

 period of their existence, if not the only one, and the natural 

 term of their life ends when this is accomplished. In their 

 previous states, however, they often pass a much longer time, 

 the length of which depends, in great measure, upon the 

 nature and abundance' of their food. Thus maggots, which 

 subsist upon decaying animal or vegetable matter, come more 

 quickly to their growth than caterpillars and other insects 

 which devour living plants ; the former are appointed to 

 remove an offensive nuisance, and do their work quickly ; 

 the latter have a longer time assigned to them, corresponding 

 in some degree to the progress or continuance of vegetation. 

 The facilities afforded for obtaining food influence the dura- 

 tion of life ; hence those grubs that live in the solid trunks 

 of perennial trees, which they are obliged to perforate in 

 order to obtain nourishment, are longer lived than those that 

 devour the tender parts of leaves and fruits, which last only 

 for a season, and require no laborious efforts to be prepared 

 for food. The harvest-flies continue only a few weeks after 

 their final transformation, and their only nourishment consists . 

 of vegetable juices, which they obtain by piercing the bark 

 and leaves of plants with their beaks ; and during this period 

 they lay their eggs, and then perish. They are, however, 

 amply compensated for the shortness of their life in the 

 winged state by the length of their previous existence, during 

 which they are wingless and grub-like in form, and live 

 under ground, where they obtain their food only by much 

 labor in perforating the soil among the roots of plants, the 

 juices of which they imbibe by suction. To meet the diffi- 

 culties of their situation and the precarious supply of their 

 food, for which they have to grope in the dark in their 

 subterranean retreats, a remarkable longevity is assigned 

 to them ; and one species has obtained the name of Cicada 

 septendecim, on account of its life being protracted to the 

 period of seventeen years. 



This insect has been observed in the southeastern parts of 



