INTRODUCTION. 



As the work on the insect fauna of a given region progresses, 

 it becomes essential not only for the further advancement of the 

 work, but also for the encouragement of others to take up the 

 study, to have in condensed form an index of our present knowl- 

 edge of the various orders. Furthermore, we hope that the 

 data here presented will in the future serve to show more clearly 

 to what extent the changes in the natural conditions of the 

 country are affecting the insect fauna. We are all aware of a 

 marked change in the insect life in the vicinity of Boston, due 

 in a great measure to the spraying to destroy the gipsy and brown- 

 tail moths, to the electric lights, to the clearing of woodland, 

 draining, stream pollution and other factors unavoidable in the 

 growth of large cities. Insufficient data, however, relative to 

 the former abundance and habitat of the various species, make 

 it difficult at present to arrive at any definite conclusion bearing 

 on the subject. 



In connection with other museum work and the building-up 

 of a general collection of New England insects, the writer has 

 during the past twenty seasons' collecting, specialized on the 

 Diptera and the results are in part represented in this list. 

 Since New England is a meeting ground of the boreal and the 

 austral species, it seems important to show the full distribution 

 of each species, so that the northern range of a common southern 

 species, and the southern range of an equally common northern 

 species may be readily seen. To avoid unnecessary printing 

 and yet show this distribution, a system of 35 named areas has 

 been adopted, beginning with northern Maine and ending with 

 Connecticut. In making a faunal survey of New England the 

 writer has endeavored to collect chiefly in sections having 

 marked physical conditions governing distribution, viz., the 

 coast, lakes, river valleys and mountains. Intensive collecting 

 has been done in several of the more favorably situated areas 

 where the "overlapping" of northern and southern species is 

 apparently most pronounced. Thus, at Mt. Desert, Maine, 

 the effect of the ocean in modifying temperature is most clearly 

 shown; at Mt. Washington, New Hampshire, the effect of alti- 

 tude on distribution is best illustrated; and in the Berkshires, 

 Massachusetts, both elevations and river valleys are factors 

 influencing distribution. 



On the accompanying map (Text-fig. 1) are shown the num- 

 bers corresponding to those given under the descriptions of areas. 

 Under each area are given the localities where collecting has been 

 done, the name of the collector and date of collecting. The lines 

 across the map mark the southern limit of the Canadian and 



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