Insect- Life— Land and the Air 285 



Moreover the adoption of metamorphosis by storing 

 up food during larval life, and so largely obviating 

 the necessity for feeding in the perfect stage, enables 

 the imago to devote full attention to the breeding 

 function and largely to increase the output of eggs. 

 Metamorphosis too increases the proportion of young 

 which will survive out of those hatched, since the 

 conditions of larval life are in most cases easy, and 

 the food-supply abundant. This is notably the case 

 among such insects as the Ants and Bees which provide 

 a nest to shelter the grubs, and expend their energies 

 in procuring food for 

 them. 



Insects creatures of 

 the Land and the Air. 

 — The branching air- 

 tubes of Insects, and the 

 almost universal presence 

 of wings among them, 

 mark them out as essen- 

 tially creatures of the air 

 and the land. The air 

 and, as we have seen, 



., , 1 • Fig. 157. — Ground - beetle (Carabus). 



every possible location Natural size, the left forewing or 



on the land, is thronged elytron to the left, magnified. 



with them. But it is to the air that they belong 

 primarily, since special adaptations for life on the 

 ground, or in concealed situations on plants, such 

 as under bark, appear to be secondary. Of all the 

 larger orders the Beetles show to the greatest extent 

 a tendency to give up the air for the ground ; and 

 among them can be traced stages in the complete 

 degeneration of the wings. In all Beetles only the 

 hind-wings are used for flying, the fore-wings being 

 modified to form the hardened " wing-cases " or 

 elytra (fig. 157). Within the same family of ground- 



