ORDER LEPIDOPTERA 69 



of food and there the pellet is deposited. As the larva 

 continues to eat it continues to deposit its frass pellets at 

 the extreme periphery of the mine and in a place from which 

 the parenchyma has been removed. Not a scrap of paren- 

 chyma is wasted and when the larva is mature the tiny 

 round black frass pellets are tidily ranged round the edge 

 while the central part is immaculately clean. Even the 

 moult skins may be pushed back with the remainder of the 

 rubbish. In the geometrical center between the two white 

 and transparent cuticles of the mine the fastidious larva 

 spins a shining transparent pupating chamber. 



Antispila Isabella mining in grape leaves in September 

 collects its excrement at one end of the mine on the floor. 

 In cutting out a case it chooses that part of the mine farthest 

 from the excrement. 



Many other larvae either find contact with their frass 

 less objectionable or they are less clever in avoiding it. 

 Some of them web it together with silk to make a tube into 

 which to retire from feeding. Many employ it in making 

 their pupal cases, either outlining the chamber with it as 

 does Lithocolletis basistrigella, or to strengthen the walls as 

 does Lithocolletis ostryaefoliella. In the group of Cameraria 

 (flat group Lithocolletis larvae) the food is taken in very thin 

 slices even after the third moult and the proportion of sap 

 is therefore high. The frass is consequently very fine 

 grained and rather fluid, and instead of being formed into 

 firm pellets, it is spread unevenly about in a waxy layer 

 over the floor of the mine. 



Silk spinning. In many leaf-mining larvae the ability 

 to spin shows itself only in constructing a cocoon either 

 pupating or hibernating. Some few tissue-feeders, as Anti- 

 spila, Coptodisca, etc., line with silk that portion of the 

 mine which they later remove as a case. In the Gracil- 

 ariidae the spinneret does not show itself until sap-feeding 

 is over and the second form of mouthparts is assumed. 



