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THE TRANSMISSION OF DISEASE BY FLIES.
Insects play a definite rôle in the transmission of disease, a fact which has been conclusively demonstrated over and over again. Many of the most serious ills of man are conveyed from person to person through the medium of mosquitoes, flies, lice, ticks, and other forms of vermin. How the transmission of disease is effected, the particular insects acting as carriers, and the means of combating such pests have all become matters with which the public is concerned.
Of the natural enemies of man, the fly unquestionably takes precedence over all others. Possibly there may be some tendency to accord to the mosquito this unique position, but if a careful summary be made of the activities of both flies and mosquitoes, the former, it is believed, will necessarily be rated as the more harmful and dangerous. Only recently has it been possible to convict this insect of the many crimes and misdemeanors of which it is guilty. We now know that flies, instead of being harmless insects, of moment only when they invade our food supplies, are in reality highly dangerous, and that a single fly may be responsible for the development of typhoid fever or other illness of a serious nature.
Kinds of Flies.
There are many kinds of flies, not all of which have the same structure, habits, or methods of reproduction. In a general way, however, the families resemble one another, and while the following description applies principally to house flies, with slight modifications it is applicable to other varieties as well.
The most common and widely distributed of all flies is the house fly. This insect is ordinarily present in all parts of the world and lives in practically any climate adapted to man. Nine-tenths of the flies found within or near dwellings belong to this group, although a number of other species so closely resemble house flies in appearance that differentiation may be impossible by other than experts. The favorite haunt of the house fly is the dwelling of man and it is seldom found away from human habitations.
The bluebottle, or blow fly, is a second familiar species, owing to the characteristic and disturbing noise made in its flight. It has a strong liking for the exposed surfaces of fresh meat and fruits, the former seemingly having a powerful attraction for the insect, but it is not averse to entering houses.
Bearing a strong resemblance to the bluebottle fly is the green bottle fly, which is slightly smaller and metallic green in color. I is commonly found near putrefying flesh, such as dead animals, ex creta, and similar filth. A member of this family often breeds i the excrement on the backs of sheep, the larvæ or maggots develop ing and feeding thereon, resulting in a serious pest to flockowner When the larvæ mature in either filth or flesh they are especial voracious and consume a large part of the substance on which the are developing. The fact that insects of this family alternate b tween human excreta and food products renders them especially da gerous, although their number is usually limited and they are s dom satisfied to remain within doors.
One of the most important species is the stable fly, or, as it sometimes called, the "biting stable fly." It is less often found filth than the other varieties, but owing to the fact that it is a bloo sucking fly, opportunity for the direct inoculation of persons ar animals with the organisms of disease is presented. It is this i sect which has been incriminated in the spread of anthrax. T stable fly is about the size of the common house fly and resembl it in appearance, being gray in color and somewhat more stout built. Its proboscis, however, is of an entirely different charact as campers and others can testify, being arranged for penetrati and sucking. It frequently torments horses and cattle and may ev cause detriment to stock through its activities. The insect is wide distributed. Closely allied to the stable fly is an African spec known as the tsetse fly, which is responsible for the spread of slee ing sickness, a fatal infection found in certain regions of the Afric Continent.
The "lesser house fly" is the name given to a species which, n to the house fly, is the most common indoor resident. Probal everyone has observed the useless and apparently aimless, jerky flig of this insect beneath some suspended article, such as a chandeli This fly is an early visitor, usually being found before the comm house fly is present in large numbers. Its breeding habits are t same as those of the house fly, but as it feeds less diligently a seldom alights, it is somewhat less objectionable. It strongly rese bles the house fly but is slightly smaller and more slender, bei perhaps, better adapted to flight. The larval form of this fly easily distinguished from that of the common house fly, as it is c ered with spines.
In addition to the species enumerated, many other bloodsucki and nonbloodsucking varieties are of interest. The cheese fly posits its eggs in cheese or fatty material, producing the so-cal cheese skippers. The dung and the yellow dung flies and the latr fly are so named because they develop in the excrement of anin