236 THE HOUSE FLY DISEASE CARRIER 



of the biting flies known as gad flies or horse flies, of 

 the family Tabanidse, enter houses seeking blood. They 

 bite painfully, but for the most part prefer to stay out 

 of doors, although they frequent shady situations as a 

 rule. They are common in pine woods, and the in- 

 habitants of summer houses built in such locations are 

 occasionally bothered by them to some extent. Trav- 

 elers in Alaska, where some of these gad flies abound 

 during the short and damp summer, have stated that 

 they sometimes become almost a scourge in the 

 cabins. 



The species which we are about to mention more 

 fully, however, are the commonest of the flies found 

 in houses, although their numbers are so insignificant 

 as to be almost disregarded when compared with Alnsca 

 dorncstica. 



THE CLUSTER FLY (Pollcnia rudis Fabr.) 



There is a rather sluggish fly, a little larger than the 

 house fly, which is frequently found in houses, espe- 

 cially in the spring and fall. It has a dark-colored, 

 smooth abdomen and a sprinkling of yellowish hair. 

 It is very sluggish, in the fall especially, and at such 

 times it may be picked up readily. It is subject to the 

 attacks of a fungous disease which causes it to die 

 upon window panes, where it is often seen surrounded 

 with a white efflorescence. (Fig. 22.) 



The cluster fly is a European species, and the date 

 of its introduction into the United States is not known. 

 It could easily have been brought over upon slow sail- 



