70 LEAF-MINING INSECTS 



The larvae of Tischeria spin as they mine, lining their 

 passageways with silk throughout. Gracilaria and Par- 

 ornix use silk in curling leaves. Lithocolletis larvae by its 

 use make a vaulted mine of a flat one. 



Thus we see there are many clues to the identification of 

 Lepidopterous leaf -miners ; but they are a host and with all 

 these clues their determination is not always easy. The 

 first and best clue is the name of the plant on which the 

 mine is found. Our index of host plants with lists of the 

 miners that are known to infest them should help here. 

 Then there is the form and color of the mine and of the 

 larva or pupa, the nature and arrangement of frass and of 

 silk; and finally cast skins, particularly the brownish head 

 capsules, may often be found in mines, even though the 

 mine-maker be departed, and these may assist in estab- 

 lishing the identity of the erstwhile tenant. 



