Many minor plans have been proposed for obviating or alleviating the perils and plague of invading fly swarms; several such plans may be well carried out on a private domestic scale, but one cannot expect any of them to be adopted universally. In domestic methods people will prefer some one plan, some another, whilst some will not personally aid in the work of fly destruction in any single way perseveringly. This latter circumstance emphasises the necessity of a dominant control by local authority for the safeguarding of all inhabitants, including the delinquents themselves in spite of themselves.

The plan, as detailed in the last chapter, of enticing breeding females to lay their eggs within depositories of discarded food remnants and garbage, can be practised on a smaller scale with great advantage everywhere. Kitchen refuse of many kinds, not neglecting potato and turnip parings, cabbage leaves, or even tea leaves, should all be collected in brown paper bags, which should be left open for a few days in suitable places round about the house for the free access of gravid female house-flies. Every such collection should he cremated on the third day. In a paper, read at a recent congress of the Royal Sanitary Institute, on "Destruction and Prevention of Household Pests," Dr. Gay advised rich and poor, in every household, whether or not a sanitary dust-bin was in use, instantly to wrap up in paper all such fly-breeding materials in readiness for cremation. However, to do so would be missing the much more effectual course of applying my "egg-trap" plan of collections in exposed open bags for cremation on the third day.

For indoor use insecticide methods are more suited; and the best of these are immensely more effective than some popular devices, which make a remarkable display and sell well, but which the purchasers soon become neglectful to keep in constant use. Traps in the form of wire-gauze cages, and glass non-return bottles belong to this latter class of contrivances; when seen crowded with struggling victims, the employment of such articles captivates many observers; but their real efficiency will be found to fall far short of general expectation. The explanation will be apparent when the use of the wire-cage trap is contrasted with the success of a good fly poison. Given, say, a dwelling room on a midsummer day containing ten female flies and ten idle dancing male flies; in such cases not more than half the females and one quarter of the males will get imprisoned within four or five hours by the employment of the wire-cage trap, but with a good method of setting poison nine-tenths of the females and half the males may be killed within the same period. In the case of poisoning, the dead have to be swept up, whilst fly traps have the advantage of collecting the victims; but, unless the inmates are carefully destroyed, a few will manage sometimes to escape from the traps, especially as side window light changes and daylight fades. In these fly traps it is only the perseverance of the prisoners in struggling towards outer light which prevents their exit by the entrance aperture.

Stickfast adhesive papers and suspended tapes and strings look very effective when seen crowded with accumulated captures; but, again, these "exhibition" appearances are as deceptive in suggestions of real efficiency as are the crowded cage traps last mentioned; moreover, sticky messes are not commendable or convenient articles for placing where most wanted. Truly, suspensory strings are attractive resting resorts for dancing males, but the worst agents of Beelzebub are the females, which have a keener appetite for food and for pestering humanity.

There remain for consideration insecticide poisons. A great choice of materials can be supplied by the chemist's shop, and various methods of using them have been recommended. In old times country people prepared decoctions of Amanita muscaria, the fly toadstool, a large orange-scarlet, or crimson, mushroom-shaped fungus commonly appearing in autumn in woods where birch trees abound. Strange to say, such decoction will poison flies of many kinds, although they, and many different creatures, feed with impunity on other fungi which are more deadly poisonous to mankind.

Effective poisons are such good exterminators of flies, that the main consideration is how to safely and most suitably employ them. There are some people who have an invincible aversion to the mere thought of poison purposely administered by way of food or drink, though possibly they do not have an equally strong repugnance to the use of insecticides used for stifling. However, one cannot help running counter to much misplaced sentimental humanitarianism in some people on some subjects; reasons and arguments will not move them, for they do not wish to think otherwise than as their prejudices influence them. The house-fly is itself a poisoner of our food, and it, or rather she (the offender being nearly always female), is a more dangerous and a more subtilely baneful enemy than, for instance, the human flea, which even the Brahmans or the disciples of Buddha may kill.

Fumigatory insecticides, though occasionally useful, may be left out of consideration in discussing the rival merits of means in a warfare against the house-fly.

A liquid or moist food poison employed in a safe and effective way will excel every other weapon of warfare within the house. One of the newest recommended substances is formalin, which has the advantages of being a disinfectant, a strong fly-poison not avoided by flies, and not dangerous or attractive to domestic animals. A tablespoonful of (40 per cent.) formalin should be mixed with one half pint of milk and water; this, when exposed in saucers or shallow dishes, is said to be an attractive and a fatal bait. It would be evidently dangerous and objectionable to use some other commoner poisons in the same way; but it is the opinion of some users that formalin and milk is not sufficiently alluring.

Contrary to a generally prevalent idea a powerful odour is not required as an indoor allurement for the common house-fly; again, a saucer or shallow dish with liquid contents is not a good method of presenting the fatal bait. Placed on a table, or on a window sill, or on a shelf, a saucer is liable to be tipped up and its contents spilt; moreover, the form of such receptacles is radically faulty by reason of the strenuous walking habits of the fly on the level. Out of many flies walking over a table ten or twelve may pass by, or round, an overhanging saucer's rim to one fly that will mount the same and sip inside. However, let such a saucer or plate be placed on a table upside-down, and let a slightly moist substance be placed in the shallow central depression, which ordinarily is the base, then the said ten or twelve flies will all mount and sample the moist substance, even though it be not apparently attractive in smell; an inclined plane is ever an irresistible invitation to mount and prospect the summit.

It is another great mistake to suppose that an extra tasty food material is desirable as a bait. The same kind of mistake is made by people baiting a mouse trap with toasted cheese, whilst a bit of dry bread, or better still, a green pea, would much better entice a common mouse. Strong smelling and saccharine foods immensely attract the blue-bottle and the wasp, which are thus enticed indoors and induced to become occasional visitors to our tables; but the house-fly requires little of such lures; indoors she is an inquisitive prospector, who will never pass by any moist material without testing its quality. Moreover, the use of poisoned milk, or even jam, should be rather avoided for fear of injury to dog or cat; furthermore, it is dangerous to place a piece of bread in a saucer of liquid fly-poison, as is sometimes done, to serve as a sop and as a standing stage. However, there is one good lure well worth mentioning; it is beer-dregs with or without a little sugar; moistened yeast is good, and the advantage of beer-dregs with just a little sugar is due to the mild yeast-like odour of slow fermentation, which may fail if formalin be the insecticide ingredient.

The handiest and safest preparation of fly-poison is that sold in the form of a dry flypaper, which is said to contain arsenic as the deadly ingredient. A very small piece of one of the sheets ordinarily sold should be placed on the summit of an inverted saucer; a mere spoonful of water now and then will suffice to moisten the same; there is little or no advantage in sprinkling a little sugar thereon, unless beer-dregs are added. This plan of using moistened poison paper is clean; it is safer than using a more fluid bait, and the ingredient is certainly efficient; the slightest taste thereof by an inquisitive fly ensures its speedy death. Another poison which has been recommended is a strong decoction of tea-leaves, to which a little sugar and beer may perhaps be added.

It is said that the smell of geraniums is odious to the house-fly, and so pots of these plants may be grown beneficially on window-sills. Certain other odours and scents are believed to be likewise more or less fly deterrent, but their use is not effective warfare against fly propagation. Paraffin painted on window-sills is said to be very efficient.

Flies may be easily prevented from entering the open windows of any room, which has windows only on one side, by the use of venetian or louvre blinds or shutters, or of many kinds of screens, although the apertures thereof may allow of ample room for flies to pass to and fro. If, however, there be windows on two sides of a room, then venetian blinds and the like will be useless, and window screens must have very close meshes to be effective. The house-fly will pass through netting only when there is light shining on the further side. A knowledge of this fact is very important in the planning of hospital wards. In a sick room, if there be windows on two sides, one in summer time should be darkened when the other is open for ventilation.

The protection of the larder and the screening of food should never be neglected, but what is of even greater importance is the prevention of access by flies to fÆcal matter, or to purulent and all unhealthy discharges from the sick room.