Preventive measures must constitute the supreme objective of an anti-fly crusade. The habits of the house-fly and its life-history make it clear how successful breeding may be prevented. The breeding places are local and accessible; the food substances of the larvæ are capable of being put under control; and the maggot stage is the opportune period wherein the fly plague is most obviously open to attack.
In all town and suburban parishes a house to house collection of domestic refuse and garbage must be made, not weekly, but bi-weekly in summer, and the material must be cremated in a dust destructor furnace within a few days of its collection; thus neither larvæ nor pupæ therein would survive; no alternative disposal otherwise than by cremation should be attempted. Furthermore, and above all else, only refuse collecting bins of an authorised pattern should be employed. Contrary to the prevalent idea these should not be fly-proof and not have air-tight covers; they should freely admit air all round and should encourage the access of breeding flies. They should stand preferably in open daylight places and should be egg-traps for flies which, thus encouraged, would hardly ever deposit their eggs elsewhere; the result would be that all maggots and pupæ would be inevitably cremated.
It may be objected that, if open dust-bins are used, house-flies after visiting the same may return to the house and subsequently contaminate food in the larder. There will be such a possibility, but the danger thereof can be minimised, and would in fact be nearly automatically cured, as prospective fly progeny perished. Furthermore, there are circumstances which indicate that the said danger would not be great, and anyhow nothing comparable to the baneful effects which are now endured. The worst germs are not those of newly discarded food remnants; the commonest and well-known bad smelling germ of ordinarily "tainted" meat, which is exceptionally attractive to the house-fly and the blue-bottle, is fortunately, after cooking, not so dangerous as some of those other deleterious micro-organisms mentioned in the last chapter. Taking one thing with another the balance of benefits and disadvantages will incline overwhelmingly in favour of open dust-bins, wherein food remnants may purposely become fly-blown. An improved dust-bin lid has been contrived which combines with the cover a centrally held wire-gauze "balloon" fly-trap, wherein flies will congregate and be imprisoned when attempting to leave.
Unfortunately air-tight dust-bins have been very generally recommended as a grand device of hygienic value; hence it is most necessary that unthinking people at large should be informed how much better it is to use open bins which can catch and secure for destruction prospective fly-broods. It may be asked—why not trap and kill the breeding females? The reply is that to do so will be good, as is to be explained in the next chapter; but contrivances for the latter procedure are apt to be less effectively put into general operation.
The fly swarms of mews, arising from accumulations of stable manure, will be difficult to alleviate without stringently enforced measures, but it is a mistaken notion to believe that town flies are bred in stables to such an extent that the invaders of our dwellings and town restaurants, shops, and markets, are merely or mainly the overflow of the mews. The concentration of many kinds of flies is very dense around ill-kept mews, and in midsummer-time a large percentage will be true house-flies. Frequent removal and cremation of stable manure would be quite effectual, but there is reason to think that, if proper care be taken, no such drastic procedure as cremation will be absolutely necessary, unless perhaps for the months of July and August.
There are two matters involved in sanitary stable reform—one is the proper structure of the stable floor and the treatment of the litter whilst in use for bedding; the other is the disposal of the horse droppings and the discarded litter called stable manure. If the floor be good and the bedding be well kept and fairly dry, which is often not the case, then the effective breeding of flies will be in the dung-pit and the external manure heap. From a sanitary point of view these latter are indeed almost everywhere ill-kept.
The general fate of maggots living on the floor of well-kept horse-boxes is to end their lives drowned in the drains to which they descend, when or before they pupate.
In these days of motor-cars and fewer horses the horticulturist everywhere is eager to buy good stuff; now stable manure to be good must be fresh and free from the garbage with which stable men wantonly corrupt the same, instead of consigning such extraneous refuse to a proper separate dust-bin for collection and cremation. So much can be done remuneratively with a regular supply of clean fresh manure, that it seems almost worth while transgressing the proper limits of this booklet and writing chapters on mushroom culture and on the intensive hot-bed cultivation, with the aid of "cloches" or bell glasses, called French gardening. It may be thought that such cultures will of themselves breed swarms of flies. Though such is not necessarily the case, the liability by common carelessness is very great.
The expert horticulturist has a special preparatory treatment for fresh manure intended for hot-beds; new manure in heaps rapidly "heats," and is ærated by being turned over two or three times on separate days before being packed close for the hot-bed. This process of treatment rather disagrees with the breeding of the house-fly. Mushrooms and all the fungus tribe breathe by inhaling oxygen and exhaling carbon dioxide; and so it happens that even insects which delight to feed on mushrooms, are somewhat repelled by the special atmosphere of very actively growing mycelium or spawn.
The amateur entomologist and the nature-student will observe that the flies which pester the gardener at work are mainly other than the common house-fly. The reader, nevertheless, will like to know if something more cannot be done to stable manure for exterminating maggots, whether of house-flies or the many various filth flies, already hatched and growing therein. Well, "something" indeed can be done by the use of some insecticide. Hitherto chloride of lime has been employed, but the most approved insecticide for the purpose is a solution of iron sulphate—two pounds in one gallon of water; this is said not to deteriorate the horticultural value of stable manure. However, in fine weather, the spreading out and drying of freshly received manure practically rids it of fly maggots, which cannot survive this simple procedure. The mere burial of fly-blown dung and stable litter without prior treatment is quite inefficient. Insanitary heaps of neglected manure, which terribly swarm with maggots, much deteriorate in horticultural value.