THE SERVICE AND UTILITY OF FLIES
It is often asked—have not house-flies some use in Nature? The only true
answer is that they are warning signals.
They certainly do join with a multitude of other flies in promiscuous
scavenging services, and they can be very active agents therein; but
this work only aggravates the fact of their dangerous partiality to
mankind, together with all his belongings and surroundings. These
creatures may well be imagined to have developed out of some primæval
species by reason of the increase of mankind upon this planet. The mere
presence of the house-fly denotes some nuisance more or less remote; the
local density of the brood indicates the degree and the proximity of
unsanitary conditions. Under present circumstances the visitation of the
house-fly is Nature's intimation that peril of a very insidious
character is about. Very properly, Nature's messenger will not be
denied, and pertinaciously manifests herself to us _indoors_!
It has already been explained that the scavenging service of the
house-fly can be altogether dispensed with, inasmuch as there is a
sufficiency of other less noxious flies and creatures devoted to such
work. Reflecting on the Story of Creation, and the mission of man as
first a gardener, and then, when expelled from Paradise, destined to
more laboriously cultivate the earth, it may be held to be man's
allotted duty not only to wage war against weeds, but likewise to
distinguish friends and foes of all kinds, and treat accordingly
creatures even of all branches of the animal kingdom, whether insects,
reptiles, birds, or mammals, favouring one and exterminating another.
This will be to rule the earth and "subdue it" (Genesis i. 28). Nemesis
will inevitably chastise man unless he rectifies the consequences of his
own delinquencies, whether they be direct or indirect. The "good
service" of the house-fly is comparable with that of the flea, which
performs an unwelcomed and indirect "service," inciting the housewife to
have well-swept floors and clean bedding.
The unalloyed good service of insectivorous flies is quite apparent. The
details of their life-history and a description of their different
characteristics would make an interesting volume, but the limitations of
the present work preclude such enlargement of its scope.
It certainly stands to the credit of the blue-bottle that she is by far
our best native scavenger of carrion; so good, indeed, that none other
as an assistant is needed. She may just possibly sometimes convey germs
and contaminate food, but she does not so directly assail man. Her
larger size makes her easy for exclusion from the domestic food store.
So eager and alert is the female in searching for meat, dead animals,
and fish, that our other native carrion-feeding flies are at a great
disadvantage in the struggle for existence; so prompt is she in
monopolising carrion, that would-be competitors often have to be content
with laying their eggs in less rich food materials. The blue-bottle can
withstand temperatures a few degrees colder than can those flies to
which she is nearest akin; and she seems capable somehow of sheltering
herself better. Even as late as the middle of winter, sometimes, a dead
bird may be found to be fly-blown under circumstances which indicate
that the eggs must have been laid in frosty weather, when flies are not
seen at large. The explanation is that the blue-bottle will for a short
time awake, and venture outside her retreat in a sheltered south wall,
warmed by a few hours of winter sun. She does not hibernate in early
winter in such a continuous state of rigid torpor as, for instance, does
the queen wasp; probably few or none survive the winter by a real
hibernation, the progenitors of the first spring broods emerging at a
date no earlier than do their rivals and congeners.
As a bird food or a fishing bait gentles are superior to the maggots of
any other dipterid insect. So-called ants' eggs and meal-worms are more
highly appreciated by the fancier for bird food, but they are expensive.
The pupæ called "ants' eggs" can only be had fresh for a short period of
summer, and dried stock for the rest of the year requires much labour to
obtain and prepare. Meal-worms are the cleanest and the easiest to
propagate of all similar larvæ; but they are very slow growing compared
with gentles; in the natural state the life-cycle from the egg to the
feeding worm, then the pupa or chrysalid, and finally the beetle,
_Tenebrio molitor_, occupies a twelvemonth's time; but, like many other
insects which have accommodated themselves to human surroundings, they
can increase more rapidly. By rearing a number of broods, each in a
separate vessel, and by hastening the development and propagation of
some broods more than others, meal-worms may be obtained fresh
throughout the year; the amount of trouble and attention required is
accordingly great.
The artificial rearing of gentles is easy, rapid, and cheap. Generally
it is not well or methodically managed, and consequently it is then a
horribly malodorous nuisance. However, with proper care the process can
be managed without offensiveness, and it will immensely repay all
trouble.
A more restricted variety of birds relish gentles, but no insect food is
more wholesome for any of the galinaceous tribe.
A spot in the open air, preferably sheltered from the north or east wind
and from mid-day sun, should be chosen. There an inverted earthenware
sea-kale pot or a similar vessel should be fixed on a stand or table
twenty inches high from the ground; the table should have a central hole
corresponding to that in the sea-kale pot. The hole in the pot should be
obstructed with a wire-cage strainer, or a piece of perforated wood or
metal, above which a few sticks or a bunch of straw may be placed.
[Illustration:
Fig. 6.
Apparatus for the
cleaner breeding
of gentles.
]
Fly-blown dead animals, fish, offal, or suitable food remnants should be
placed from time to time in such a receptacle, which should be
surmounted with a removable rain-proof cover and shade of ample size.
The latter should allow a two-inch space or a little more underneath all
around the rim of the pot for ventilation. Underneath the table or stand
a wide and more or less shallow pan or dish should be placed, and a
little clean sharp sand placed therein.
The gentles, whilst growing and feeding, are called "green" gentles;
their skin is transparent, and in this state chickens do not like eating
them; and it is as well so, for then the half-grown gentles would be
capable of temporarily becoming deleterious internal parasites in the
birds' crop. As soon as they are full grown they crawl away from the
food material and will fall through the strainer-like obstruction in the
bottom hole of the pot into the pan on the ground underneath. They are
then termed clean or "scoured" gentles and are fit for bird-food or for
fishing-bait.
If taken out of the pan and placed in boxes with a little sand, they
will keep three days, more or less, according to the weather; they then
pupate, and in a few days, or weeks, or months, according to
temperature, emerge as blue-bottles. As pupæ they are good and
convenient food for domestic fowls, and for all pheasants and like
game-birds.
If receptacles as above directed are situate in a fowl-run, the hens
will never leave the ground dish unwatched as long as full fed gentles
are maturing. Hens thus fed are prolific layers of eggs, but of course
they must be otherwise fairly fed with farinaceous and suitable other
food and healthy grit. The maggots of no other flies are worth similarly
cultivating; those that feed on vegetable refuse are more offensive in
smell than common gentles; the maggots of the fungus flies are
comparatively clean creatures and free from bad smell, but the largest
are small.