— ia INSECTS AND DISEASE Fig. 1. THE FILTH FLY (J/usca domestica) a. Auxiliary vein i; Antenne b. First longitudinal vein g- Transverse suture ¢. Fourth longitudinal vein h. Squama d. Discal cell i. Abdomen e- Anal cell j- Tibia THE FILTH FLY Musca domestica More volumes have been written about this insect in the last twenty years than have been devoted to any other one insect (unless it be the honey-bee) since man became civilized enough to write about insects at all.
This fly is commonly called the “‘house fly,”’ but that name has been justly criticized because it seems to imply a necessary domestic relation. We do not believe that this insect should be a /ouse fly in the future; and Dr. L. O. Howard of Washington, in view of its relation to disease, has suggested that is should be called the Typhoid Fly. This seems, on the other hand, to relate rather too closely a disease and an insect which are sometimes, but not universally, connected. Filth Fly is perhaps the best term and one that is undoubtedly applicable. The fly breeds in filth, it resorts to filth, and it carries filth with it everywhere it goes. 5
AMERICAN MUSEUM GUIDE LEAFLETS The excellent figures given here, combined with common experience, are sufficient for the identification of the “‘ordinary house fly,”’ or ‘‘typhoid fly,” or “filth fly.”” Note (Figs. 1 and 4) especiaily the rounded angle in the fourth longitudinal vein, the plumose antennal bristle, the absence of stout bristles on the abdomen, the absence of a vertical row of bristles between the base of the hind legs and the “balancers,”’ and the absence of a prominent bristle near the middle of either middle tibia. As is the case with many other Diptera, the males of this species have the eyes closer together than do the females. The sides of the abdomen in the male are brownish near the base and grayish elsewhere. The females are grayish over the whole abdomen with a variable pattern of darker gray or black. The filth fly, like all other Diptera, passes through four definite stages in its life cycle: egg, larva, pupa, and adult. The egés of the fly (one or two hundred in number) are laid by preference in horse manure but may also be deposited in almost any moist decaying organic matter, such as ‘““human excrement, pig manure, decaying grain, moist bran, moist mixtures of hay and grain from feed troughs | of animals, excreta-soiled straw, contents from slaughtered animals, decaying kitchen refuse, rotting fruits and vegetables, excreta-soiled paper and rags, and ensilage.’’ Dr. Howard estimates that probably 90% of our filth flies are hatched from horse manure. Only certain portions of a manure pile are, however, favorable for fly breeding, ‘“‘a layer some inches deep and lying a few inches below the surface where there may be found a moderate amount of heat and moisture, an excess of either being fatal or compelling migration.” It takes the eggs of the fly about twelve hours, on the average, to hatch. The larve are whitish creatures, blunt at the posterior end and pointed in front. They have no bristles or hairs. On the blunt end are spiracles or breathing holes. In young larve these spiracles are in a heart-shaped aperture; later they appear in two slits; and still later in three winding slits. The changes occur when the larve cast their skins at intervals during their growth while feeding on the manure or other material in which they live. About five days after hatching, the maggot, now about half an inch long, burrows downward into the ground or outward into the drier portions of the manure and there changes to a brownish pupa about % inch long. The pupal stage may last from three or four days to several weeks, and recent observations suggest that autumn broods usually pass the winter in this form, although the fly may 6 *— —— e
INSECTS AND DISEASE Fig. 2. EGGS, LARVA AND PUPA OF THE FILTH FLY (Photograph of models in The American Museum of Natural History) - /
AMERICAN MUSEUM GUIDE LEAFLETS hibernate in any stage. Atthe termination of the pupal stage the fly comes out of the pupal case and crawls up to the surface of the material in which it pupated. Here its wings quickly harden and it is ready to fly away. The rate at which generations of flies follow each other is determined by the temperature. Studies made in the Laboratory of Public Health of the American Museum gave a total period from egs laying to the emergence of the adult of 9.3 days at 35° C., 10.3 days at 30° C., and 22.3 days at 20° C. , The adult fly lives upon liquid food, since its mouth parts are in the form of a sucking proboscis, but by discharging a free flow of saliva it is able to turn foods like sugar into the fluid form it can absorb. Fig.3 e - ‘ z % é d ; c ; ) 8 ‘ ee: SSE ee | ee a ee oe! — +.
INSECTS AND DISEASE Fig. 4. THE FILTH FLY (Musca domestica) ( Photograph of model in The American Museum of Natural History)
AMERICAN MUSEUM GUIDE LEAFLETS RELATIVES OF THE FILTH FLY There are a number of other flies sometimes found in houses which may be mistaken for the Filth Fly, and the characteristics of a few of them may be briefly described.
Homalomyia canicularis is often supposed to be a “‘young house fly.’ It does look like a small edition of the more common and dangerous insect; but it is a wholly different species. No insect grows after it has attained to the dignity of wings. The wing-veins of Homalomyia run without a sharp bend to the margin of the wing. This creature is really not even a muscid; it belongs to the Anthomyide. It breeds in waste organic matter such as manure. Muscina is a muscid genus. Our species may be recognized by the fact that they are black flies a _— and not shining; the meat ee dian stripe on the thorax is light, the fourth longitudinal vein is only slightly bent and the first posterior AY: Csmer. cell is scarcely contracted at the margin; the hind end of the thorax may be reddish. MW. stabulans has the legs and palpi more or less yellowish, while those of W. assimilis are wholly black. The larve feed on excrement and a variety of decaying substances including fungi and vegetables. Pollenia rudis is known as the “‘cluster fly’’ from the habit which the adults have of congregating in masses, especially about the ceilings of rooms, when they are looking for a place in which to hibernate. When mashed, these flies are very Sreasy and have an odor which has been described by some as like honey and by others as “very disagreeable.”’ They breed, as parasites, in earthworms. The thorax has no distinct stripes and is usually covered with a yellowish ““dust’’; the space between the eyes is white, the fourth longitudinal vein is sharply bent. | The genus Lucilia includes the “‘Sreen- and blue-bottle flies.”’ Both the thorax and abdomen are bright and metallic. This description would apply also to certain other Muscide, but it has not been Fig. 5. THE ELE BOUSE FLY (Homalomytacanicularts) 10
——— INSECTS AND DISEASE i! Colema i“. “HG, w ws Fig. 6. THE STABLE FLY (A/uscina stabulans) Fig. 7. THE BLUE-BOTTLE FLY (/.uci/ia c@sar) 11
AMERICAN MUSEUM GUIDE LEAFLETS shown that the “‘bottles’’ are instrumental in transmitting diseases and a further diagnosis would require going into details which would be out of place here. The larve feed chiefly on carrion but those of L. cesar occur also in garbage and excrement. These notes on various Muscidze (in a broad sense) and an Anthomyid have been given for the purpose of introducing the table given below.’ It will be seen from this table that the only fly which is very abundant on human excrement and also in dining rooms is Musca domestica. This is the principal reason why this fly is so dangerous.
Flies found in Dining Rooms Very Moderately Abundant Po uendene | Abundant Rare ~ cee Reet =| Pan we 5 ot ee oe meee e Very Musca | Borborus © Abundant domestica CQUINUS | <| Abundant _ Muscina | Sarcophaga = stabulans SAVVACENIE 5 = Ophyra a leucostoma = | 2 | Pseudopvrelia < COYnICcINa S .
2 Myospila ” | meditabunda an ve ee a Moderately Homalom ya Lucilia | | Abundant canicularis | cesar Drosophila FPollenia ampelophila rudts / Rare ) | ; | Stomoxvs | Calliphora | calcitrans \erythrocephala 1Reprint from the /ze/d Fook of Insects (G. P. Putnam’s Sons), by Frank E. Lutz. It may not be out of place to say that this book gives further details, which cannotbeincludedhere,concerningtheidentificationandhabitsofotherinsectswhichare troublesome but not actually dangerous.
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