INSECTS AND DISEASE BITING FLIES Stomoxys calcitrans. If ordinary house flies seem to be adding to their other vices by biting, it is a case of mistaken identification; the culprits are almost certainly the Stomoxys calcitrans, the “biting stable fly.”’ Its proboscis is long, slender, and pointed, not fleshy and blunt as is that of Musca domestica (page 5). The name, stable fly, is not very appropriate, as this fly is neither the most abundant fly about stables, as a rule, nor does it breed chiefly about stables unless a quantity of wet, fermenting hay or straw be present. Piles of lawn-cuttings or of weeds furnish more Stomoxys than do ordinary stables. Adults are more frequently found about buildings in damp weather and just before a storm than at other times, for which reason the saying has arisen that the biting of flies isa sign of astorm. The best method of control is self-evident—do away with the breeding places either by destroying the material, covering it so that flies do not have access to it, or drying it so that the larve cannot live. AV Getemaa.
"6 Fig. 8. THE BITING STABLE FLY (,S/omo.xvys calcitrans) The most conspicuous biting flies in the Northeastern United States belong to the Tabanidz and are variously called “‘horse flies,” ““gad flies,” and “‘green-headed flies.” The head is large; each antenna has three joints, the last being somewhat subdivided into from four 13
AMILACAN MOSEOGOM (GOIDE - LEAFLETS to eight parts; the eyes are large and usually brightly colored when the insect is alive; the proboscis is sometimes as long as, or longer than, the body; the thorax and abdomen bear hairs but not bristles; each wing has two submarginal and five posterior cells; the anal cell is usually closed but not far before the border of the wing; the marginal vein runs entirely around the wing. The larve are aquatic, or semi-aquatic, and predacious. They taper at both ends and each of the eleven segments into which the body is divided bears a circlet of small spines. The adults fly by day, usually being found in warm sunny places, though some prefer shady woods. Only the females bite; both sexes feed on the juices of plants and on similar substances. There are several hundred species recorded from North America. The only other biting Calypterate which we have in the Northeast is Hematobia serrata, the ‘““Horn fly.” It is less than half the size of Stomoxys calcitrans and the palpi are nearly as long as the proboscis, while in Stomoxys they are much shorter than the proboscis. The genus Glossina includes the tsetse flies; it is found only in Africa at the present time, although it formerly occurred in America, as is proved by fossils unearthed in Colorado. The tsetse flies are as large as, or larger than, Musca domestica, the ordinary house fly; the waist is constricted; the wings are crossed when at rest; the fourth longitudinal vein bends before it meets the very oblique anterior transverse vein. Both sexes bite, usually by day, but also at night if the moon be bright. The larve almost complete their development within the body of their mother and are then laid at the roots of plants. The pupal stage lasts from six to eight weeks. Several species have been described and their habits carefully studied but, owing to the facts that the larve are carried by the female until nearly or quite full-grown and that the adults feed on the blood of other animals than man, control methods are difficult.
Certain insects are not real transmitters of disease but are themselves its inciting agents. There are, for instance, dipterous larve, ‘maggots,’ which occur by accident or as a part of their normal lifehistory in the human body. Such an occurrence is cailed myiasis. The most important species in this connection is the “‘screw-worm, ” Chrysomyia macellaria. It is a blow fly which has been classed with the Muscide and also with the Sarcophagide. The adult fly is nearly, or quite, half an inch long; metallic green; with three longi- 14
INSECTS AND DISEASE tudinal dark stripes on the thorax; its head is reddish to yellowish brown; its wing venation is similar to that of J/usca domestica. Several hundred eggs (sometimes the eggs hatch before they are laid and then living larvae are deposited) are placed on carrion or in wounds or sores in living animals. In the case of man, the eggs are usually laid in the nostrils of those suffering from nasal catarrh. The yellowish-white larva has rings of bristle-like structures on the segments, which give it the appearance of a screw. If it is not removed from the nostril, it may work in, causing an abscess and even death. Blow flies of the genus Calliphora (Muscide with metallic colored abdomen but dull colored thorax; fourth longitudinal vein sharply bent; distal third of antennal bristle bearing some hairs; cheeks unicolorous) sometimes lay their eggs on cold meat, especially pork, and the larvz are then taken into the stomachs of careless eaters. Usually not much harm is done. The same is true of Lucilia (see page 10). The CEstride are closely related] to the Muscidz but the adults have rudimentary mouth-parts. They are the bot flies, and certain species do great damage to stock. In tropical America human beings are parasitized by the CEstrid Dermatobia hominis, and possibly other species. The larve live underneath the skin of various parts of the body. William B. Herms, in his useful Medical and Veterinary Entomology (Macmillan Medical Co., New York), gives a key to the larve ordinarily involved in myiasis.
AMERICAN MUSECOM- GOIDE, LEAFLETS THE FILTH FLY AND DISEASE Musca domestica is not only a pest but a serious menace to health on account of the likelihood that it may carry filth from the unsavory places which it frequents to food. The foot of the fly is tipped with claws and soft pads on which there is ample room for great numbers of microbes to be transplanted; and, as a matter of fact, if a fly be allowed to walk over the surface of a properly prepared bacterial culture plate, the path over which it travels is marked by numerous Fig.9 colonies of bacteria, each developed from a single germ planted there by the foot of the insect. Even more serious, perhaps, is the danger that disease germs ingested by a fly from privy contents, or other infected material, may be voided in its excrement (fly specks) or in small droplets which are regurgitated by the insect. Experiments have shown that many kinds of disease germs may pass through the intestines of the fly and be discharged in its excrement in an active and virulent state.
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INSECTS AND DISEASE The spoiling of foods may obviously be hastened by ordinary putrefactive germs introduced in such ways and, if the fly has been feeding upon human discharges (tuberculous sputum for example, or the contents of an outside closet used by an incipient typhoid case) specific human diseases may easily result.
Fig. 10. BACTERIAL COLONIES DEVELOPED ON AN AGAR PLATE FROM GERMS PLANTED BY THE FEET OF A FLY WHICH WALKED OVER IT The number of microbes actually carried by flies varies greatly with the general amount of filth in their surroundings. Studies made by the New York Association for Improving the Condition of the Poor gave an average of 13,986 bacteria per fly (on the outer surfaces of its body) in clean localities, against 1,106,017 in dirty surroundings. The germs of typhoid fever and Asiatic cholera have been isolated from the bodies of flies caught during epidemics of these diseases, and we have, in our museum of living bacteria at the American Museum, one strain of typhoid bacilli isolated in this way in the course of an outbreak in New Jersey.
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__ AMERICAN MUSEUM GUIDE LEAFLETS It was the experience of the American troops in the Spanish War which first forcibly called attention in this country to the danger of the transmission of disease by flies. About one out of five of our volunteer soldiers contracted typhoid during the campaign, and the investigators who studied the cause of this disastrous affair concluded that ‘“‘the number of cases of typhoid fever in the different camps varied with the methods of disposing of the excretions.’ The typhoid germs, in most cases, were probably spread from person to person by more or less direct contact, but the fly undoubtedly played its part. Doctors Reed, Vaughan and Shakespeare pointed out in their official report that “flies swarm over infected fecal matter in the pits and then deposit it and feed upon the food prepared for the soldiers at the mess tents. In some instances, where lime had recently been sprinkled over the contents of the pits, flies with their feet whitened by lime were seen walking over the food.’’ ‘The investigators also point out that, “‘Officers whose mess tents were protected by means of screens suffered proportionately less from typhoid fever than did those whose tents were not so protected,” and again that ““Typhoid fever gradually disappeared in the fall of 1898 with the approach of cold weather and the consequent disabling of the flies.”’ In the World War flies have constituted a grave menace to the health of troops operating in tropical and semitropical regions. On the western front they have been remarkably well controlled by burning manure and garbage and by protecting latrines. At Gallipoli and in Egypt, however, they have been responsible for the spread of dysentery and many other parasitic diseases among the French and English troops.
The most striking evidence in regard to the importance of the fly as a carrier of disease is, perhaps, that furnished by the experience of Jacksonville, Fla. Ever since the encampment of troops at Jacksonville in 1898 the city has been heavily infected with typhoid fever. No reliable data are available before 1908, but the typhoid death rates per 100,000 population for the years 1908, 1909, and 1910 were 82, 75 and 106 respectively. In the late summer of 1910 a law was passed requiring that all dry closets within the city should be rendered fly-proof. By March, 1911, about 75 per cent. of the closets had been brought into conformity with the law and the typhoid rate for the year dropped to 63. By January, 1912, practically all the closets had been rendered fly-proof and the typhoid rate dropped to 26. 18 are a.
INSECTS AND DISEASE The danger of transmission of disease by flies increases with the extent to which human excreta are exposed to the access of flies and with the duration of the warm season, which favors fly breeding. Danger is not confined, however, to unsewered rural districts or to the South. The Association for Improving the Condition of the Poor in New York City made a careful study of the relation between flies and infant diarrhea in the summer of 1914. Nearly 1000 infants were carefully observed, half of them being in ordinary homes and half in homes where special efforts were made to protect the infant and his food from flies. The homes studied were classified according to their general cleanliness and according to their freedom from flies. In the homes where flies were abundant, 1.9 times as many infants suffered from summer diarrhea as in the homes protected from flies, and 1.8 times as many were attacked under dirty conditions as in the clean homes. Where both factors were combined, in dirty and fly-ridden homes, there were 2.4 times as many infants who suffered from diarrhea as in the clean and fly-protected tenements. PREVENTION OF FLY-BORNE DISEASE The practical methods of controlling the spread of disease by flies fall under four main headings: the prevention of fly breeding, the destruction of adult flies, the protection of human discharges from access of flies, and the protection of food by screening houses and covering the food itself.
PREVENTION OF FLY BREEDING The usual methods employed in fighting the dangerous Muscidz are really of little avail. Sticky fly-paper, wire flytraps, and poisons will undoubtedly kill a large number but infinitely more are breeding where they came from. Screening our windows and doors will undoubtedly keep many out but it is not pleasant to live in a cage. Furthermore, the people from whom we buy our milk and other food-stuffs may not beso careful. The only thoroughgoing method is to stop the trouble at its souree—prevent fly breeding. The adults we kill cannot thereafter breed, but they have probably done so before and many of their companions are sure to escape altogether. If we could do away with the breeding places, or make them unfit for fly larve, or keep adult flies away from them, the thing would be done. Nearly all the books and lecturers say that this is easy. It is well to be optimistic but better to recognize the whole truth. It cannot be done easily.
AMERICAN MUSEUM -GOIDE LEAFLETS If anti-fly campaigns are to be successful your neighbor must keep his place clean too, for his flies are just as apt to come into your house as his, so the problem becomes one for the whole community. This is the heart of the matter. A few earnest individuals or wellmeaning Improvement Societies, by themselves, can do little more than cause a great deal of trouble and very little good. Laws must be made and enforced so that the ignorant or careless may not make of little or no avail the work of the intelligent and careful. Since 90 flies out of every 100 are probably born in a manure pile, the elimination of the natural breeding places of the fly means, first and foremost, the proper care of stable manure. Stables should not have dirt floors, since it has been shown that the ground moistened by animal discharges contains many larve and pupz. Floors should be water-tight, preferably of cement, and constructed so as to drain freely into a sewer or covered cement pit. In wooden floored stables flies should be excluded from the ground beneath the floor boards. Openings left for ventilation should be screened with wire and no holes should be bored in the floor for drainage of urine. Fig. 11. MODEL SHOWING A GOOD TYPE OF MANURE BIN (AmericanMuseumofNaturalHistory) The surface of the manure is being sprinkled with a chemical to prevent fly breeding. - 20 el