* a? i} No. 71, REVISED EDITION. nited States Department of Agriculture, BUREAU OF ENTOMOLOGY, L. O. HOWARD, Entomologist and Chief of Bureau. HOUSE FLIES. (Musca domestica et al.) By L. O. Howarp. There are several species of flies which are commonly found in houses, although but one of these should be called the house fly proper. This is the Musca domestica L. (fig. 1) and is a mediuni-sized, grayish fly, with its mouth parts spread out at the tip for sucking up liquid sub- stances. It breeds in manure and dooryard filth and is found in nearly all parts of the world. On account of the conformation of its mouth Fig. 1.—Common house fly (Musca domestica): Puparium at left; adult next; larva and enlarged parts at right. All enlarged (author’s illustration). parts, the house fly can not bite, yet no impression is stronger in the minds of most people than that this insect does occasionally bite. This impression is due to the frequent occurrence in houses of another fly (Stomoxys calcitrans L.) (fig. 2), which is called the stable fly, and which, while closely resembling the house fly (so closely, in fact, as to deceive anyone but an entomologist), differs from it in the important particular that its mouth parts are formed for piercing the skin. It is perhaps second in point of abundance to the house fly in most portions of the Northeastern States. A third species, commonly called the cluster fly (Pollenia rudis Fab.), is a very frequent visitant of houses, particularly in the spring and fall. This fly is somewhat larger than the house fly, with a dark-colored, smooth abdomen and a sprinkling of yellowish hairs. It is not so active as the house fly and, particularly in the fall, is very sluggish. At such 2 times it may be picked up readily and is very subject to the attacks of a fungous disease which causes it to die upon window panes, surrounded by a whitish efflorescence. Occasionally this fly occurs in houses in such numbers as to cause great annoyance, but such occurrences are comparatively rare. A fourth species is another stable fly, known as Muscina stabulans Fall. (fig. 3), a form which almost exactly resembles the house fly in general appearance, and which does not bite as does the biting stable fly. It breeds in decaying vegetable matter and in excrement. Several species of metallic greenish or bluish flies are also occasion- ally found in houses, the most abundant of which is the so-called blue- bottle fly (Calliphora erythrocephala Meig.). This insect is also called the blow-fly or meat-fly and breeds in decaying animal material. A smaller species, which may be called the small blue-bottle fly, is Phormia ‘ Fia. 2.—Stomozys calcitrans: Adult, larva, puparium, and details. All enlarged (author's illustration). terrenove Desv. (fig. 4); and a third, which is green in color and about the size of the large blue-bottle, is Lucilia cwsar L. (fig. 5). There is still another species, smaller than any of those so far men- tioned, which is known to entomologists as Homalomyia canicularis L., sometimes called the small house fly. A related species, H. brevis Rond., is shown in figure 6. H. canicularis is distinguished from the ordinary house fly by its paler and more pointed body and conical shape. The male, which is much commoner than the female, has large pale patches at the base of the abdomen, which are translucent when the fly is seen on a window pane.. It is this species that is largely responsible for the prevalent idea that flies grow after gaining wings. Most people think that these little Homalomyias are the young of the larger flies, which, of course, is distinctly not the case. Still another fly, and this one is still smaller, is a jet-black species known as the window fly (Scenopinus fenestralis L.), which in fact has 3 become more abundant of later years. It breeds in the dust under carpets, and its larva is a white, very slender, almost thread-like creature. In the autumn, when fruit appears on the sideboard, many specimens of a small fruit-fly (Drosophila ampelophila Loew) (fig. 7) make their appearance, attracted by the odor of overripe fruit. A small, slender fly is not infrequently seen in houses, especially upon window panes. This is Sepsis violacea Meig., shown enlarged in figure 8. All of these species, however, are greatly dwarfed in numbers by the com- mon house fly. In 1900 the writer made collections of the flies in dining rooms in different parts of the country, and out of a total of 28,087 flies 22,808 were Musca do- : Fig. 3.—Muscina stabulans, enlarged mestica ; (author’s illustration). that is,98.8 per cent of the whole number captured. The remainder, consisting of 1.2 per cent of the whole, comprised various species, including those mentioned above. LIFE HISTORY OF THE TRUE HOUSE FLY. Musca domestica commonly lays its eggs upon horse manure. This substance seems to be its favorite larval food. It will ovi- Fie. 4.—Phormia terreenove, enlarged posit on (author’s illustration). cow ma- nure, but we have not been able to rear it in this substance. It will also breed in human excrement, and from this habit it becomes very dangerous to the health of human beings, carrying, as it does, the germs of intestinal dis- eases such as typhoid fever and cholera from excreta to food supplies. It will also lay its eggs upon other decaying vegetable and animal material, but of the flies that infest dwelling houses, 5 Ree Fic. 5.—Lueilia cesar, enlarged (author’s both in cities and on farms, a vast illustration). proportion comes from horse manure. At Salem, Mass., Packard states that he bred a generation in four- teen days in horse manure, The duration of the egg state was twenty- q four hours, the larval state from five to seven days, and the pupal state from five to seven days. At Washington the writer has found in mid- summer that each female lays about 120 eggs, which hatch in eight hours, the larva period lasting five days and the pupa five days, making the total time for the development of the generation ten days. This was at the end of June. The periods of development vary with the climate and with the season, and the insect hibernates in the puparium condi- tion in manure or at the surface of the ground under a manure heap. It also hibernates in houses as adult, hiding in crevices. The Washington observations indicate that the larve molt twice, and that there are thus three distinct larval stages. The periods of development were found to be about as follows: E Fic. 6.—Homalomyia brevis: Female at left: male next, with enlarged antenna’ larva at right. All enlarged (author's illustration). first mo]t, one day; first to second molt, one day; second molt to pupa- tion, three days; pupation to issuing of the adult, five days; total life round, approximately ten days. There is thus 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 is undoubtedly large, averaging about 120, and the enormous numbers in which the insects occur is thus plainly accounted for, especially when we consider the abundance and universal occurrence of appropriate larval food. In order to ascertain the numbers in which house-fly larve occur in horse- manure piles, a quarter of a pound of rather well-infested horse manure was taken on August 9, and in it were counted 160 larve and 146 puparia. This would make about 1,200 house flies to the pound of manure. This, however, can not be taken as an average, since no larve are found in perhaps the greater part of ordinary horse-manure piles. Neither, however, does it show the limit of what can be found, since about 200 puparia were found in less than 1 cubic inch of manure taken - dD from a spot 2 inches below the surface of the pile where the larve had congregated in immense numbers. The different stages of the insect are well illustrated in figure 1 and need no description. REMEDIES AND PREVENTIVES. A careful screening of windows and doors during the summer months, with the supplementary use of sticky fly papers. is a preventive measure against house flies known to everyone, and there seems to be little hope in the near future of much relief by doing away with the breeding places. A single stable in which a horse is kept will supply house flies for an extended neighborhood. People living in agricultural commu- nities will probably never be rid of the pest, but in cities, with better methods of disposal of garbage and with the lessening of the number of horses and horse stables consequent upon electric street railways, bicycles, and automobiles, the time may come, and before very Fic. 7.— Drosophila ampelophila: a, adult; b, antenna of same; ec, base of tibia and first tarsal joint of same; d, puparium, side view; e, puparium from above; f, full-grown larva; g, anal spiracles ofsame. All enlarged (author’s illustration). long, when window screens may be discarded. The prompt gathering of horse manure, which may be variously treated or kept in a specially prepared receptacle, would greatly abate the fly nuisance, and city ordi- nances compelling horse owners to follow some such course are desir- able. Absolute cleanliness, even under existing circumstances, will always result in a diminution of the numbers of the house fly, and, in fact, most household insects are less attracted to the premises of what is known as the old-fashioned housekeeper than to those of the other kind. During the summer of 1897 a series of experiments was carried out with the intention of showing whether it would be possible to treat a manure pile in such a way as to stop the breeding of flies. The writer’s experience with the use of air-slaked lime on cow manure to prevent the breeding of the horn fly suggested experimentation with different = 6 lime compounds. It was found to be perfectly impracticable to use air- slaked lime, land plaster, or gas ime with good results. Few or no larvee were killed by a thorough mixing of the manure with any of these three substances. Chlorid of lime, however, was found to be an excellent maggot killer. Where 1 pound of chlorid of lime was mixed with 8 quarts of horse manure, 90 per cent of the maggots were killed in less than twenty-four hours. At the rate of a quarter of a pound of chlorid of lime to 8 quarts of manure, however, the substance was found not to be sufficiently strong. Chlorid of lime, though cheap in Europe, costs at least 384 cents a pound in large quantities in this country, so that the frequent treatment of a large manure pile with this substance would be out of the question in actual practice. Experiments were therefore carried on with kerosene. It was found Fig. 8.—Sepsis violacea: Adult with enlarged antenna at right; puparium at left. All enlarged (author’s illustration). that 8 quarts of fresh horse manure sprayed with 1 pint of kerosene, which was afterwards washed down with 1 quart of water, was thor- oughly rid of living maggots. Every individual was killed by the treatment. This experiment and others of a similar nature on a small scale were so satisfactory that it was considered at the close of the season that a practical conclusion had been reached, and that it was perfectly possible to treat any manure pile economically and in such a way as to prevent the breeding of flies. Practical work in the summer of 1898, however, demonstrated that this was simply another case where an experiment on a small scale has failed to develop points which in practical work would vitiate the results. The stable of the U. 8S. Department of Agriculture, in which about twelve horses are kept, is situated about 100 yards behind the main building of the Department and about 90 yards from the building in 4 which the Bureau of Entomology is situated. This stable has always been very carefully kept. The manure was thoroughly swept up every morning, carried outside of the stable, and deposited in a pile behind the building. This pile, after accumulating for a week or ten days, or sometimes two weeks, was carried off by the gardeners and spread upon distant portions of the grounds. At all times in the summer this manure pile swarmed with the maggots of the house fly. It is safe to say that on an average many thousands of perfect flies issued from it every day, and that at least a large share of the flies which constantly bothered the employees in the two buildings mentioned came from this source. On the basis of the experiments of 1897, an attempt was made, beginning early in April, 1898, to prevent the breeding of house flies about the Department by the treatment of this manure pile with kero- sene. The attempt was begun early in April and was carried on for some weeks. While undoubtedly hundreds of thousands of flies were destroyed in the course of this work, it was found by the end of May that it was far from perfect, since if used at an economical rate the kero- sene could not be made to penetrate throughout the whole pile of’ manure, even when copiously washed down with water.