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 very erratic in all its motions. It is preyed on 











i fuEeLd 
Fig. 129.—vifferent stages of house and blow-flies. Enlarged. After Taschenberg. 
in Europe by two kinds of ichneumon-flies, whose larvee feed 
inside of their host; also by a fly-parasite( Astoma parasiticum). 
It is a pity that these useful parasites have not as yet been 
introduced into this country. We already possess, however, 
one fly-parasite in this country (Astoma musearum) (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 inthe 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 carnarva Lann.). 
Many other flies, although they do not actually bite man 
or beast, become a great nuisance and torment by running 
over them in search of liquid food, perspiration. Nearly all 
