DIPTERA OF MINNESOTA. 



71 



The perfect flies, that is, the imagoes or adult insects, are about 

 one-eighth of an inch long, more or less downy or velvety, a "humped" 

 thorax and the short antennae consisting of ii joints. They breed 

 in running water, hence they are particularly abundant in the northern 

 part of Minnesota, where, for them, ideal summer conditions exist. 

 The writer, in a trip to Labrador several years ago, found them un- 

 bearable a short distance from the coast, and was glad to flee back 



Fig. 60. S. ventistum, female, and eggs. Lugger. 



to the shore. They are nearly as bad, quite bad enough, in this state. 

 In the northern part of Minnesota in ordinary seasons, they begin 

 to be troublesome a little before the first of June. Oil of citronella, 

 used as for mosquitoes, is effective as long as the skin is moist with 

 the same. Louis Agassiz refers feelingly to their attacks, in "Lake 

 Superior," and even such an enthusiastic coleopterist as E. A. 

 Schwartz has been obliged to give up collecting insects in localities 



