The House Fly and How to Suppress It | Page 3

days.
The pupa stage is easily affected by temperature changes and may be
prolonged during hibernation for as long as 4 or 5 months. Numerous
rearing experiments in various parts of the country have shown that the
shortest time between the deposition of eggs and the emergence of the
adult fly is 8 days, and 10 and 12 day records were very common.
The adult fly, upon emerging from the puparium, works its way upward
through the soil or manure and upon reaching the air it crawls about
while its wings expand and the body hardens and assumes its normal

coloration. In from 2 1/2 to 20 days, as previously stated, the female is
ready to deposit eggs. As in the case of other periods of its life history,
so the preoviposition period is prolonged considerably by the lower
temperatures of spring and fall. In midsummer, with a developmental
period of from 8 to 10 days from egg to adult, and a preoviposition
period of from 3 to 4 days, a new generation would be started every 11
to 14 days. Thus the climate of the District of Columbia allows
abundance of time for the development of from 10 to 12 generations
every season.
[Illustration: FIG. 7.--Pupæ of the house fly. About natural size.
(Newstead.)]
Flies usually remain near their breeding places if they have plenty of
food, but experiments recently made at Dallas, Tex., show that they
may migrate considerable distances; in fact, house flies, so marked that
the particular individuals could be identified, have been recaptured in
traps as far as 13 miles from the place where they were liberated.

HOW THE HOUSE FLY PASSES THE WINTER.
The prevailing opinion that the house fly lives through the winter as an
adult, hiding in cracks and crevices of buildings, etc., appears to be
erroneous. Under outdoor conditions house flies are killed during the
first really cold nights, that is, when the temperature falls to about 15°
or 10° F. In rooms and similar places protected from winds and
partially heated during the winter flies have been kept alive in cages for
long periods, but they never lived through the entire winter. In
longevity experiments one record of 70 days and another of 91 days
was obtained. No uncaged house flies were found during three seasons'
observations in unheated and only partially heated attics, stables,
unused rooms, etc., where favorable temperature conditions prevailed.
The common occurrence in such places of the cluster fly and a few
other species, which may be easily mistaken for the house fly, is
responsible for the prevailing belief as to the way the house fly
overwinters. There is therefore no reliable evidence whatever that adult

house flies emerging during October and November pass the winter and
are able to deposit their eggs the following spring, although they may
continue active in heated buildings until nearly the end of January. On
the other hand, there is evidence that house flies pass the winter as
larvæ and pupæ, and that they sometimes breed continuously
throughout the winter. In experiments at both Dallas, Tex., and
Bethesda, Md., house flies have been found emerging during April
from heavily infested manure heaps which had been set out and
covered with cages during the preceding autumn. In the Southern States,
during warm periods in midwinter, house flies may emerge and become
somewhat troublesome; they frequently lay eggs on warm days.
The second way in which the house fly may pass the winter is by
continuous breeding. House flies congregate in heated rooms with the
approach of the winter season. If no food or breeding materials are
present they eventually die. However, where they have access to both
food and suitable substances for egg laying they will continue breeding
just as they do outdoors during the summer. Even in very cold climates
there are undoubtedly many places, especially in cities, where house
flies would have opportunity to pass the winter in this manner.

CARRIAGE OF DISEASE BY THE HOUSE FLY.
The body of the house fly is covered thickly with hairs and bristles of
varying lengths, and this is especially true of the legs. Thus, when it
crawls over infected material it readily becomes loaded with germs, and
subsequent visits to human foods result in their contamination. Even
more dangerous than the transference of germs on the legs and body of
the fly is the fact that bacteria are found in greater numbers and live
longer in its alimentary canal. These germs are voided, not only in the
excrement of the fly, but also in small droplets of regurgitated matter
which have been called "vomit spots." When we realize that flies
frequent and feed upon the most filthy substances (it may be the excreta
of typhoid or dysentery patients or the discharges