30 LEAF-MINING INSECTS 



about either. They are too small to be very attractive to 

 the larger and more familiar animals, and too small to be 

 readily observed by us when sought out and eaten, as doubt- 

 less they are, by warblers, creepers and nuthatches. For- 

 bush says that the beet leaf-miner is eaten by chipping 

 sparrows. At Picton, Nova Scotia in 1908 there was a heavy 

 infestation of birch leaves by sawfly that over winter in a 

 circular silken hibernaculum within the leaves. Dr. 

 Matheson found most of the hibernacula empty, with a 

 small hole in one side, wherein, presumably, some bird had 

 extracted the larvae. Many larvae are taken from their 

 winter quarters by mice and shrews. When one sees a 

 little red squirrel sitting among the fallen leaves under a red 

 oak tree, tossing a handful of leaves and cocking his head 

 on one side as if intently listening, it is easy to imagine that 

 he is trying to catch the sound of a loose pupa of the beetle 

 Brachys, tumbling about within its mine. Dr. Martin 

 Hering in his comprehensive work on "the Ecology of leaf- 

 mining Insects/ ' mentions inquilines and symbiotic dwellers 

 namely; thrips, fungi, yeasts and bacteria, in the mines of 

 these insects. 



Predaceous insects are rather more commonly observed. 

 Webster and Parks (1913) record a species of mite (Ery- 

 thraens sp.?) attacking the larvae, of Agromyza pusilla 

 within the mines. One of us (Frost) has seen the bug, 

 Nabis feras feeding on larvae of Pegomyia calyptrata, and 

 Chrysopa rufilabris feeding on Agromyza jacunda. The 

 Nabis has also been reported as an enemy of the beet leaf- 

 miner. More is known concerning parasites because every 

 one who tries to rear leaf-miners finds emerging in his cages 

 plenty of these instead. In the beginning, the mine may 

 have been a place of comparative security from parasites, 

 but it is not so now. Once the parasites has learned how to 

 effect an entrance, the miner is worse off than its free-living 

 ancestor, having no means of escape. A very high percent- 

 age of parasitism is the rule among leaf -miners. 



