THE VINE SAW-FLY. 523 



dark brown veins. The body of the female (Fig. 244) 



measures one quarter of an inch in length, that 



of the male is somewhat shorter. These flies 



rise from the ground in the spring, not all at 



one time, but at irregular intervals, and lay 



their eggs on the lower side of the terminal leaves of the 



vine. 



In the month of July the false caterpillars, hatched 

 from these eggs, may be seen on the leaves, in little 

 swarms, of various ages, some very small, and others fully 

 grown. They feed in company, side by side, beneath the 

 leaves, each swarm or fraternity consisting of a dozen or 

 more individuals, and they preserve their ranks with a 

 surprising degree of regularity. Beginning at the edge 

 they eat the whole of the leaf to the stalk, and then go to 

 another, which in like manner they devour, and thus pro- 

 ceed, from leaf to leaf, down the branch, till they have 

 grown to their full size. They then average five eighths 

 of an inch in length, are somewhat slender and tapering 

 behind, and thickest before the middle. They have twenty- 

 two legs. The head and the tip of the tail are black ; the 

 body, above, is light green, paler before and behind, with 

 two transverse rows of minute black points across each 

 ring ; and the lower side of the body is yellowish. After 

 their last moulting they become almost entirely yellow, and 

 then leave the vine, burrow in the ground, and form for 

 themselves small oval cells of earth, which they line with 

 a slight silken film. In about a fortnight after going into 

 the ground, having in the mean time passed through the 

 chrysalis state, they come out of their earthen cells, take 

 wing, pair, and lay their eggs for a second brood. The 

 young of the second brood are not transformed to flies until 

 the following spring, but remain at rest in their cocoons in 

 the ground through the winter. 



For some years previous to the publication of my Dis- 

 course, I observed that these insects annually increased 



