INJURIOUS INSECTS. 267 



«pecies, beyond what is accomplished by its natural enemies and 

 destroyers, this might readily be effected, by selecting out the 

 galls in the winter season, when they show conspicuously upon 

 the leafless twigs, gathering them, and consigning them to the 

 flames. 



Habits. — From an inspection of the galls formed by the C. Sa- 

 licis, it would seem that their growth is caused in the following 

 mode. The parent deposits an egg at the tip of a twig of the 

 willow, when it is growing vigorously, and is of a succulent tex- 

 ture. Probably this is in the month of June. The larva, on 

 I hatching, gradually eats its way downwards in the pith of the 

 I -shoot, entirely consuming this as it advances, and thus forming the 

 canal which runs longitudinally through the centre of the gall. 

 This consumption of the pith causes the extreme and tenderest 

 part of the twig where the young worm begins, to wither and die, 

 jforming the horn-like siunmit of the gall. The juices of the plant 

 now flow to this part more copiously, either in consequence of the 

 irritation produced by the worm, or (if we may consider this to 

 jhave any analogy to what takes place in the animal economy un- 

 ider similar circumstances) an inflammation excited to produce a 

 'separation between the gangrened and living textures, or both 

 these causes combined. The part hence receiving an unusual 

 quantity of the nutritive fluids of the plant, becomes preternatu- 

 ifally developed into the fully formed gall, with its woody texture, 

 Iforming a secure residence for the worm during the winter season 

 which ensues. And often, one, two or three of the buds upon the 

 sides of the gall are also stimulated into activity, and shoot forth, 

 forming small branches implanted upon its walls. 



At or near the bottom of the canal within the gall, the larva 

 lies during the winter season, with its head upwards. The perfect 

 .insects are readily obtained at this time, by placing a few of these 

 ^lls in a tumbler coveied with paper and kept in a warm room. 

 Thus situated, their metamorphoses are completed in eighteen or 

 :wenty days — scarcely one of them failing to produce a fly. 



A thin, white, membraneous-like partition^ is placed across the 

 bpper part of the canal within the gall, with its edges reflected 

 lownwards, and lining the inside of the cavity for a short dis- 

 ance ; when ready to undergo its final change, the pupa, by a wrig- 

 gling motion, crawls upwards, and rupturing this partition, ascends 



