168 Insect Architecture. 



oblong elevations caused by small splinters of the wood, 

 detached at one end, but left fixed at the other, by the insect. 

 These elevations are for the most part in a line, rarely in a 

 double line, nearly at equal distances from each other, and 

 form a lid to a cavity in the wood about four lines in length, 

 containing from four to ten eggs. It is to be remarked that 

 the insect always selects a branch of such dimensions that it 

 can get at the pith, not because the pith is more easily bored, 

 for it does not penetrate into it all, but to form a warm and 

 safe bed for the eggs. M. Pontedera says, that when the 

 eggs have been deposited, the insect closes the mouth of the 

 hole with a gum capable of protecting them from the weather ; 

 but M. Eeaumur thinks this only a fancy, as, out of a great 

 number which he examined, he could discover nothing of the 

 kind. Neither is such a protection wanted ; for the woody 

 splinters above mentioned furnish a very good covering. 



The grubs hatch 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 chrysa- 

 lides, but into active nymphs, remarkable for their fore limbs, 

 which are thick, strong, and furnished with prongs for dig- 

 ging ; and when we are told, by Dr. Le Ferve, 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 con- 

 formation 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 Vallisnieri, an eminent Italian naturalist, in a 

 four-winged fly, most appropriately denominated by M. Eeau- 

 mur the saw-fly (Tenthredo), of which many sorts are in- 

 digenous to Great Britain. The grubs from which these flies 

 originate are indeed but too well known, as they frequently 

 strip our rose, gooseberry, raspberry, and red currant trees of 

 their leaves, and are no less destructive to birch, alder, and 



