196 A BOOK OF INSECTS 



they not only assist sanitation in all parts of the world, 

 but also promote the speedy transmutation of effete 

 organic matter into its simple chemical constituents. In- 

 deed, the importance of insects as agents in this neces- 

 sary resolving process can hardly be exaggerated. As we 

 have seen, the raw material which goes to form organic 

 bodies is built up in the first instance by green plants. 

 But it is only lent for the purpose, so to speak, and as 

 soon as it has served its turn putrefaction sets in. In 

 other words, the once living matter is reconverted by 

 ordered stages into those inanimate substances of which 

 it was originally formed. Sir Ray Lankester tells us that 

 " this breaking down of the chemical compounds of dead 

 bodies into a condition in which they can serve as the food 

 of plants is effected by excessively minute, but ubiquitous 

 and enormously abundant colourless organisms — the 

 actual chemical agents of putrescence and fermentation — 

 known as bacteria. Were there no bacteria, the nitrogen 

 and carbon of dead plants and animals would remain 

 locked up as proteid, fat, and sugar. The surface of the 

 earth would be strewn — even covered in — by the enor- 

 mous accumulation of dead, unchanging bodies, and then 

 life would become extinct, for there would be no food for 

 the green plants." But while this is true, it is also a fact 

 that bacteria, notwithstanding their abundance, would be 

 unable to perform their task without the intervention of 

 insects. The latter, by comminuting the tough fibres of 

 dead plants, constitute a kind of "speeding up" agency 

 whereby the ultimate dissolution by bacteria is greatly 

 accelerated. Moreover, the destruction of living plants 

 by insects is doubtless part of the same great scheme, and 

 beneficial in the main to the world at large. Mr. R. B. 

 Henderson has suggested that, but for the voracity of 

 grubs and caterpillars, probably " too many leaves would 



