House Flies

(Family Muscidae.)The insects of this family comprise what might be known as the typical true flies. The bristle of the antennae is feathery and the abdomen is smooth except for a certain number of bristles near the tip. The larva as a rule feed upon decaying animal or vegetable matter, more abundantly upon animal than vegetable. The group comprises many species and includes some of the most common and abundant forms, such as the house fly (Musca domestica), the horn fly of cattle (Haematobia serrata), the stable fly (Stomoxys calcitrans), and some of the so-called "blue bottle" flies. Certain members of this group, such as the horn fly, and the stable fly (both species having been introduced from Europe) are very annoying t0 live stock and produce great loss by their attacks.Many species of this group are of much value as scavengers, destroying, through their great number and quick breeding, quantities of decaying animal matter, but some of them are again injurious as appears from recent investigations by virtue of the fact that they breed in human excrement through the carriage and distribution of the germs of diseases of the intestinal tract..Typical Life History(Musca domestica.)This insect, known as the common house fly, is found all over the world. It lays its eggs by preference in horse manure but in the absence of this substance will oviposit and breed in other excrementitious matter and will lay its eggs in decaying vegetables, although I have been unable to rear it in substances of the last named character. It is also difficult and often impossible to rear it from cow dung. In horse manure, however, it flourishes. The eggs are laid freely on horse manure in an undisturbed condition. These eggs are elongate, white, and hatch very soon after being laid, in six or eight hours. The larvae, which are white, pointed maggots, as shown in the accompanying figure, grow rapidly, cast their skin twice, and reach full growth under favorable conditions in four or five days. The outer skin then hardens, swells out, turns dark brown in color, and within it the true pupa is formed. In this stage it may live for five days and the adult fly issues at the expiration of this time through a round hole in the anterior end of the pupal covering. This makes the total life round for a single generation in summer approximately ten days. Thus there is abundance of time for the development of twelve or thirteen generations in the climate of Washington every summer.The number of eggs laid by an individual fly averages about 120 and the enormous numbers in which the insect occurs is thus plainly accounted for, especially when we consider the abundance and universal occurrence of appropriate larval food. The universal occurrence of uncared for piles of horse manure in cities is therefore not only a source of great discomfort but is inimical to health since the house fly undoubtedly distributes disease germs. The numbers in which house fly larvae occur in horse manure piles may be understood when the statement is made that from a quarter of a pound of manure from the center of a pile 160 larva; and 146 puparia of the house-fly were taken. This would make about 1200 house flies to the pound of manure. This is not a fair average, but indicates possibilities and is an actual record of an individual case. Experiments conducted by the writer at Washington indicate that by cleanly measures in stables, by the daily collection of the manure and placing it in a closed pit or closet or by treating it at intervals of a week with chlorid of lime, the house fly nuisance can be greatly abated and thus the disease danger largely avoided.There is a general impression that house-flies sometimes bite people, but this is entirely wrong. Their mouth parts are fitted for sucking and lapping up liquids, and not for piercing. The stable fly mentioned in a previous paragraph is, however, a biting one, and it looks so much like a house fly that one almost has to let it bite before finding out whether it is a house fly or not. The stable fly is seldom found in houses except just before a rain, and then it comes in at the open windows. From this fact arises the old saying, "Flies begin to bite before a rain". It has been asked why flies seem to prefer windows and looking­glasses, but the answer is simple enough: when they are on the windows they want to get out; when they are on looking­glasses they are mistaking them for windows.Sometimes when a house fly is examined it will be seen to be fairly covered with little reddish objects which are really living creatures. They are parasitic mites which attach themselves to the bodies of house flies and certain other insects and inserting their long beaks suck their juices. It is comforting to think that the house fly has these parasites which torment him so. Such retribution is just. And there is another comforting fact: house flies die of fungus diseases. Sometimes, especially in the fall, flies will be found behind the picture-frames or in rather dark places, covered with a gray, fur-like substance, which is the manifestation of the fungus disease which has killed it. Then, too, dead flies will be seen with their bodies swollen and appearing more or less striped. These also have been killed by another fungus disease. These epidemic diseases cease in December, and although many thousands of house flies are killed by them, the remarkable rapidity of development in the early summer months soon more than replaces the thousands thus destroyed.