
AMERICAN MUSEUM GUIDE LEAFLETS 

The excellent figures given here, combined with common experi- 
ence, are sufficient for the identification of the “‘ordinary house fly,”’ 
or ‘‘typhoid fly,” or “filth fly.”” Note (Figs. 1 and 4) especiaily the 
rounded angle in the fourth longitudinal vein, the plumose antennal 
bristle, the absence of stout bristles on the abdomen, the absence of 
a vertical row of bristles between the base of the hind legs and the 
“balancers,”’ and the absence of a prominent bristle near the middle 
of either middle tibia. As is the case with many other Diptera, the 
males of this species have the eyes closer together than do the females. 
The sides of the abdomen in the male are brownish near the base 
and grayish elsewhere. The females are grayish over the whole 
abdomen with a variable pattern of darker gray or black. 
The filth fly, like all other Diptera, passes through four definite 
stages in its life cycle: egg, larva, pupa, and adult. The egés of the 
fly (one or two hundred in number) are laid by preference in horse 
manure but may also be deposited in almost any moist decaying 
organic matter, such as ‘““human excrement, pig manure, decaying 
grain, moist bran, moist mixtures of hay and grain from feed troughs | 
of animals, excreta-soiled straw, contents from slaughtered animals, 
decaying kitchen refuse, rotting fruits and vegetables, excreta-soiled 
paper and rags, and ensilage.’’ Dr. Howard estimates that probably 
90% of our filth flies are hatched from horse manure. Only certain 
portions of a manure pile are, however, favorable for fly breeding, 
‘“‘a layer some inches deep and lying a few inches below the surface 
where there may be found a moderate amount of heat and moisture, 
an excess of either being fatal or compelling migration.” 
It takes the eggs of the fly about twelve hours, on the average, 
to hatch. The larve are whitish creatures, blunt at the posterior 
end and pointed in front. They have no bristles or hairs. On the 
blunt end are spiracles or breathing holes. In young larve these 
spiracles are in a heart-shaped aperture; later they appear in two slits; 
and still later in three winding slits. The changes occur when the 
larve cast their skins at intervals during their growth while feeding 
on the manure or other material in which they live. 
About five days after hatching, the maggot, now about half an 
inch long, burrows downward into the ground or outward into the 
drier portions of the manure and there changes to a brownish pupa 
about % inch long. The pupal stage may last from three or four 
days to several weeks, and recent observations suggest that autumn 
broods usually pass the winter in this form, although the fly may 
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