Gall-Beetles. 



417 



small snow- white tuft of downy-looking substance floating 

 about on the wind, as if animated. Those tufts of snow- 

 white down are never seen in numbers at the same time, 

 but generally single, though some dozens oi them may be 

 observed in the course of one day, This singular object is 

 a four- winged fly (Eriosoma populi, LEACH), whose body is 

 thickly covered with long down a covering which seems 

 to impede' its flight, and make it appear more like an inani- 



Galls produced on the leaves and leaf-stalks of the Poplar by Eriosoma popui, t with the 

 various forms of the insects, winged, not winged, and covered with wool, both of the 

 natural size and magQified. 



mate substance floating about on the wind, than impelled 

 by the volition of a living animal. This pretty fly feeds 

 upon the fresh juices of the black poplar, preferring that of 

 the leaves and leaf-stalks, which it punctures for this 

 purpose with its beak. It fixes itself with this design to a 

 suitable place upon the principal nervure of the leaf, or 



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