82 LEAF-MINING INSECTS 



encd, and the thoracic legs are present at least during the latter 

 part of the larva's life as a miner. The abdominal segments are 

 prominently enlarged on each side, giving the larva the appear- 

 ance of a coleopterous larva. When ready to leave its mine the 

 larva is about 1J mm. in length. The full-grown larva is about 

 [5 mm.] I inch in length. 



When the larva has completed its growth in the mine, it cuts 

 its oval case out of the mine, apparently always making the lower 

 piece slightly larger than the upper one. It then walks out on the 

 leaf and deftly turns the case over so that the thicker piece from 

 the lower epidermis is on top. The larva grows slowly, occupying 

 all of June and July and part of August to attain its full growth. 



The process of cutting and removing a piece of the leaf for 

 enlarging the case is an interesting one. The larva when feeding 

 attaches its case to the leaf by short silken cords at intervals about 

 the edges. Each cord is composed of many threads spun in such 

 a manner that they cross one another near the middle and form 

 an X-shaped cord. When ready to get a new piece for its case, 

 the larva usually cuts a narrow oval slit in the leaf a little distance 

 out from the edge of the case and all of the way around it, so that 

 the piece, when cut, is considerably larger than the case. The new 

 piece, which supports the case with the larva inside, is always held 

 in place while the cutting is going on, by tiny strands of leaf tissue 

 which the caterpillar keeps for supports until it is ready to com- 

 plete the process. Sometimes the process is varied, the larva 

 cutting a half-oval slit in the leaf extending about halfway around 

 the old case, then cutting a half oval about the opposite end of the 

 case, and joining the ends of the two slits, thus completing the 

 circle. Evidently the larva drags the case to either the upper or 

 the under side of the leaf, as the circumstances require. The 

 position of the case when it is clear of the opening, however, is 

 another matter, for it often requires orientation. If the larva 

 drags its case to the under side of the leaf, the larger piece is on its 

 back, properly oriented; but if the larva crawls to the upper side 

 of the leaf, the larger piece is still on the bottom of the case and the 

 whole case must be turned over, and the larva must also turn over 

 inside of the case. The whole operation of cutting around the case 

 and actually cutting it loose from all support while the larva is 



