April, '15] 



SHELFORD: ORIGINAL INSECT HABITATS 



173 



In the forest area lakes and ponds formed by glaciation and the 

 ^'oxbows" by rivers often filled with vegetable detritus and become 

 covered over T^dth a low wet meadow, a part of which may be under 

 water in spring. Such situations were originally common throughout 

 the eastern portion of the United States, particularly where glaciation 

 has taken place, but are by no means wanting in other localities. 

 These moist m^eadows nearly always were surrounded by forest and 

 the boundaries between them were forest edges. A forest edge is a 

 thicket made up of rank weeds on the side nearest the meadow; inside 

 of these are various shrubs arranged in belts and increasing in height 

 as we go toward the forest. Considering the marsh meadows and 

 associated forest edges we find on comparing lists of species collected 

 from these situations with the works inentioned above, that more 

 than one-half of the phj'tophagus species are mentioned as impor- 

 tant. 



Turning to the species which frequent the higher and drier ground 

 and which are found under the same conditions as crop pests, we find 

 that the steep lake (PL 7, fig. 2) and river bluffs, the bare rocks expos- 

 ures upon which trees do not grow, support numbers of them. The 

 bare steep bluffs are the haunts of the dry bare ground frequenting 

 forn:s like Dissosteira Carolina and the vegetation supports aphids, 

 locustids, and beetles of great economic importance. 



The forest encroaches upon these situations as a shrub thicket sim- 

 ilar to the moist forest edge. These shrubby thickets are made up of 

 hawthorn, wild plum, with occasional cherr}^, gooseberry, cottonwood, 

 willow, etc. These are the headquarters of the pests of small fruits, 

 apples, etc., and preeminently the headquarters of the orchard birds. 

 These shrubby thickets of the river banks, etc., are duplicated on the 

 flood plain itself where hawthorn, grape, currant grow either in open 

 scattered formation or in dense thickets. These thickets support the 

 majority of our native pests of the fruit-bearing trees and shrubs. 



III. The Original Distribution of Native Pests. — Considering 

 the distribution of the marsh and moist vegetation inhabiting species, 

 we find that on the whole it is exceptionally wide, and similar to the 

 distribution of the marshes themselves, and within wide range of cli- 

 matic conditions represented by the greater part of the United States 

 and Southern Canada (except the arid southwest) and a northward 

 extension in the plains and prairie region of western Canada (Fig. 10). 

 Some of the species common in the swamps of New England may be 

 found on the prairies at Edmonton and the grassy marshes of the lower 

 Mississippi and along the irrigation ditches of the Rio Grande in New 

 Mexico. 



The species occupying the higher drier bare ground, and scattered 



