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53
Provided the conditions are favourable, the whole developm nt
from the egg to the perfect fly may be accomplished in about 9 or
10 days, and 14 days later the second generation may be depositing
eggs.
THE HABITS OF THE HOUSE FLY—The most particular
and prominent of these is the habit of constant feeding. It seems
tobe indifferent to the fly, whether it feeds on the putrid contents
of the bust-bin or the food on our tables; and it will pass from one
to the other with the utmost impartiality. It is this special
feature of its life, which renders it so dangerous.
The fly cannot take solid food. It must dissolve all solids
before taking them into its digestive system; and this it does by
means of its saliva, which is produced in abundance by its salivary
glands, of which it has two. The ducts of these glands are connected
to a single tube which opens into the mouth On a suitable
stimulus, the saliva is secreted, and poured out upon the particle
the fly desires to dissolve and absorb. The fluid food is then sucked
up by a powerful sucking arrangement, with which it is provided,
first into its crop, then at leisure into the proventriculus, and afterwards
into the stomach, where it undergoes digestion. Another
prominent habit of the fly is that of returning its food from the
crop, in the form of large drops of liquid. Some of these drops are
deposited on the surface upon which the fly is resting. It matters
not where that may be, whether on the rim of the milk jug or the
dust-bin. These drops are known as "vomit spots." In most cases
they are re-absorbed by the fly. The "vomit spots" are distinguishable
from the excreta spots by being of light colour, the latter
being brown.
Another habit of the fly is its activity. This is so well known
as to become proverbial. Connected with its activity is its range
of flight. This has been ascertained to be about a mile.