236 THE HOUSE FLY—DISEASE CARRIER 
of the biting flies known as gad flies or horse flies, of 
the family Tabanidje, 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 Musca 
domestica. 
The Cluster Fly (Pollenia 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- 
