62 LEAF-MINING INSECTS 



leaves for all to read will speak more plainly than an adult 

 caught on the wing or a larva pickled in a bottle. These last 

 are objects on which systematists and anatomists can do 

 and have done careful and useful work; but the mines in the 

 leaves confront even the casual observer; sometimes they 

 affect economically the gardener, the fruit-grower or the 

 farmer; and they are things of absorbing interest to the 

 general naturalist or ecologist. 



Tenancy. In life habits mining caterpillars differ from 

 one another in the proportion of their immature stages given 

 over to living in mines. Some are miners but for a short 

 part of their larval life, afterwards emerging to feed outside ; 

 some spend all of their larval life in the leaf but emerge to 

 pupate, while still others spend all larval and pupal stages 

 in the mine and emerge first as adults. The accompanying 

 diagram will illustrate these differences, together with the 

 relation they bear to sap-feeding and to tissue-feeding habits. 



Most of those that leave the mine as fairly young larvae 

 have some definite shelter during the remainder of their 

 feeding stages. Parornix and Gracilaria, for instance, spin 

 a web to fold or curl the leaves, and then feed within the 

 chamber so made. Most of the mining Gelechias either 

 fold the leaves or web several leaves together in late larval 

 life. Scythris matatella according to Chambers makes a 

 web on the under side of the leaves of Giant Ragweed, 

 Ambrosia trifida, and mines from this shelter in small 

 patches. Gnorimoschema scutellariaella similarly, is said to 

 make a shelter of silk, but here in the shape of a tube or 

 case covered externally with frass. From the narrower end 

 of this case it passes into the interior of the leaf of the skull- 

 cap, Scutellaria lateriflora, to feed. 



The Coleophoras, case-bearers, as their names suggest, 

 make cases by cutting out and sticking together portions of 

 the walls of the mine. These instead of being fixed and 

 stationary as in the Gnorimoschema, are portable. 



