152 INSECT ARCHITECTURE. 



out of a great number which he examined, he could 

 discover nothing of the kind. Neither is such a pro- 

 tection wanted; for the woody spUnters above men- 

 tioned furnish a very good covering. 



The grubs hatched from these eggs (of which, M. 

 Pontedera says, one female will deposit from five to 

 seven hundred) issue from the same holes through 

 which the eggs have been introduced, and betake 

 themselves to the ground to feed on the roots of 

 plants. They are not transformed into chrysalides, 

 but into active nymphs, remarkable for their fore 

 limbs, which are thick, strong, and furnished with 

 prongs for digging; and when we are told by Dr Le 

 Fevre, that they make their way easily into hard stiff 

 clay, to the depth of two or three feet, we perceive 

 how necessary to them such a conformation must be. 



Saw-flies. 



An instrument for cutting grooves in wood, still 

 more ingeniously contrived than that of the tree- 

 hopper, was first observed by Valisnieri, an eminent 

 Italian naturalist, in a fore-winged fly, most appro- 

 priately denominated by M. Ktaumur the saw-fly 

 (Tenthredo), of which many sorts are indigenous to 

 Great Britam. The grubs from which those flies 

 originate are indeed but two well known, as they fre- 

 quently strip our rose, gooseberry, raspberry, and red 

 currant trees of their leaves, and are no less destruc- 

 tive to birch, alder and willows; while turnips and 

 wheat suffer still more seriously by their ravages. These 

 grubs may readily be distinguished from the cater- 

 pillars of moths and butterflies, by having fiom six- 

 teen to twenty-eight feet, by which they usually hang 

 to the leaf they feed on, while they coil up the hinder 

 part of their body in a spiral ring. The perfect flies 

 are distinguished by four transparent wings; and 



