THE BLOW-FLY. 



155 



Several kinds of true worms {Nematodes) are found in the 

 house-fly. Sometimes they are very numerous, and if the 

 detached head of the fly is pressed between two flat pieces of 

 glass they can readily be seen. As many as seventeen have 

 been counted in the head of a single fly, and it is no wonder 

 that this fly showed all symptoms of insanity, being perfectly 

 reckless and ver\' erratic in all its motions. It is prej'ed on 



^ 1^ fa\'->-j 



Fig. 129. — Different stages of house and blow-flies. Enlarged. After Taschenberg. 



in Europe by two kinds of ichneumon-flies, whose larvae feed 

 inside of their host; also by a ^y-'{^Q:^sc&\tQ:{Astonia'pam8iticinii). 

 It is a pity that these useful parasites have not as yet been 

 introduced into this countr_v. We already possess, hov^^ever, 

 one fly-parasite in this country {Astoma imisearum) (fig. 47). 

 You have no doubt seen small red dots upon the base of the 

 wings of our fly (fig. 46, plate VII). This red dot is the 

 parasite just mentioned, and let us hope that it may increase 

 at the same ratio as all his relatives are in the habit of doing. 

 Fig. 129 shows house-flies and blow-flies upon a bone; also 

 their earlier stages." 



THE BLOW-FLY OR FLESH-FLY. 



{Sarcophaga carnarla Linn.). 



Many other flies, although they do not actualh'bite man 



or beast, become a great nuisance and torment hy running 



over them in search of liquid food, perspiration. Nearh^ all 



