FLY LEAF-MINERS. 249 



these winding whitish paths, increasing in width from the point 

 of their commencement; but the agent of their excavation, 

 instead of being the caterpillar of a tiny moth, is the grub of a 

 minute fly, which, when enclosed in its little brown barrel-like 

 puparium, may easily be detected, on holding up the leaf against 

 the light. 



In speaking of the common house-fly, we have noticed 

 already a species closely resembling it, which, on a scale pro- 

 portioned to its size, carries on its mining operations between 

 the membranes of dock-leaves, causing thereby those brownish- 

 red transparent blotches by which they are so commonly 

 disfigured. Striking, certainly, is the contrast, in their early 

 stages, between the lives of our caterpillar "Miners " and those 

 of their little brethren the "Stone-masons" and "Tent-makers." 

 These, instead of having only to enter at once upon a path of 

 peace and plenty, are compelled, before they touch a morsel of 

 their respective viands, to labour hard at the erection of houses 

 of defence, exposed meanwhile to the prying eyes and devouring 

 bills of insect and biped enemies. Herein, besides contrast, 

 would seem inequality of condition and yet perhaps (as with 

 the seeming inequalities of human life) the balance of enjoyment 

 between these labouring and non-labouring insects may be more 

 nicely adjusted than on first sight appears. In compensation 

 for his greater amount of labour, who knows but that certain 

 pleasant sensations of repose, satisfaction, and security, un- 

 known to the mining idler, may not be experienced by the 



