20 



LEAF-MINING INSECTS 



mine of L. lucetiella is located on the underside of a linden 

 leaf between strong veins, and it remains quite flat to the 

 end. But the mine of L. morissella on the underside of the 

 thin and weakly braced leaf of the hog-peanut, becomes 

 completely folded together in a single ridge: collapsed- 

 tentiform, so to speak. (See fig. 41.) 



Certain portions of the leaf are preferred by different 

 leaf-miners, some, like Brachys, choosing the vicinity of 



Fig. 11. Leaf-maps of mine distribution. A, 50 mines of Bracks sp.? 

 on Basswood (note their scarcity within the central circle); B, 50 mines of 

 Antispila viticordifoliella on wild grape (general); C, 100 mines of Litho- 

 colletis ostryarella on hop hornbean (note avoidance of the leaf margin). 



the stronger veins, and others avoiding these as much as 

 possible. 



FRASS 



As an African hunter follows his big game by taking note 

 of its spoor, and as an ornithologist learns something of the 

 habits of owls from the examination of their pellets, so the 

 student of leaf -mining insects may gather much information 

 concerning their identity and their behavior from an ex- 

 amination of their frass. 2 This varies with their food, 



1 Frass is the rejectamenta of their food (as the name implies) left in 

 the mine after feeding, and of their feeding operations: fecula, chips, etc., 

 collectively. 



