THE BALANCE OF NATURE 129 



fungus. The Bronze Fly (Gymnochaeta viri- 

 dis), Plate XI., Fig. 11, is not uncommon 

 about walls and hedges in bright sunshine. 

 Its brilliant metallic green body, with bronze 

 reflections, shines with dazzling radiance. 

 The Dung Fly (Scatophaga stercoraria), Plate 

 XI., Fig. 12, is one of Nature's scavengers. 

 It is of a downy yellow colour. Annoying as 

 flies often are, we must never forget that they 

 generally serve a most useful function in 

 removing matter, which would otherwise 

 pollute the air. If it were not for these flies, 

 and the beetles of similar habits, the country 

 would soon be uninhabitable. 



In this chapter there is an illustration of 

 the manner in which Nature preserves an 

 even balance in her several parts. The larva 

 or maggots of two-winged flies remove 

 putrescent matter, but, if unchecked, they 

 would soon increase to such a degree as to 

 become noxious. Amongst the checks pro- 

 vided are those powerful insects of prey, the 

 dragonflies, whose voracity tends to keep the 

 swarms of Diptera within due bounds. They, 

 in their turn, are restrained by the attacks of 

 birds ; and thus, so long as man does not 



