200 INSECTS INJURIOUS TO VEGETATION. 



sap that nourishes them. Reaumur observed the ground quite 

 moist under peach-trees infested with bark-hce, which was caused 

 by the dripping of the sap from the numerous punctures made by 

 these insects. While they continue their exhausting suction of 

 sap, they increase in size, and during this time are in what is call- 

 ed the larva state. When this is completed, the insects will be 

 found to be of different magnitudes, some much larger than the 

 others, and they then prepare for a change that is about to ensue 

 in their mode of life, by emitting from the under-side of their 

 bodies numerous little white downy threads, which are fastened, in 

 a radiated manner, around their bodies to the bark, and serve to 

 confine them securely in their places. After becoming thus fixed 

 they remain apparently inanimate ; but under these lifeless scales 

 the transformation of the insect is conducted ; with this remark- 

 able difference, that, in a few days the large ones contrive to 

 break up and throw off, in four or five flakes, their outer scaly 

 coats, and reappear in a very similar form to that which they be- 

 fore had ; the smaller ones, on the contrary, continue under their 

 outer skins, which serve instead of cocoons, and from which they 

 seem to shrink and detach themselves, and then become perfect 

 pupae, the rudiments of wings, antennae, feet, &c., being discov- 

 erable on raising the shells. If we follow the progress of these 

 small lice, which are to produce the males, we shall see, in pro- 

 cess of time, a pair of threads and the tips of the wings protruding 

 beneath the sliell at its lower elevated part, and through this little 

 fissure the perfect insect at length backs out. After the larger 

 lice have become fixed and have thrown off their outer coats, they 

 enter upon the pupa or chrysalis state, which continues for a 

 longer or shorter period according to the species. But when 

 they have become mature, they do not leave the skins or shells 

 covering their bodies, which continue flexible for a time. These 

 larger insects are the females, and are destined to remain im- 

 movable, and never change their place after they have once be- 

 come stationary. The male is exceedingly small in comparison 

 to the female, and is provided with only two wings, which are 

 usually very large, and lie flatly on the top of the body. After 

 the insects have paired, the body of the female increases in size, 

 or becomes quite convex, for a time, and ever afterwards remains 



