The flies and their cousins, the gnats, are not only pests, but dangerous enemies of mankind.
Entirely aside from their role as carriers of disease, they can do serious harm by their biting habits. The mouth parts of the flies differ somewhat in the different families, but all consist of a needle-like projection which can penetrate any kind of skin to perfection.
After getting underneath the skin and before sucking up the blood, which is the object of the maneuver, most of the flies, as well as the mosquitoes, inject a small drop from their salivary glands to dilute the blood or juices of the host. This salivary secretion is very irritating in most species and in some, actively poisonous.
Black flies, sometimes called buffalo flies, or hump-backed flies, are the worst. They are fortunately not very much at home in civilization, but in the woods and fields they make life miserable for the fisher-man and farmer.
The bites of black flies are irritating and painful when made, but become even more so in the course of three or four days. The swelling, inflammation, general poisoning, and loss of blood from the bites breaking open have often caused death in man, and among domestic animals is so common as to amount to a considerable economic loss.
They breed in running streams, which makes their annihilation more difficult than mosquito larvae which are born in still ponds. Rivers which overflow their banks in the black fly country, however, can be banked so as to prevent overflow, and this has been found to reduce the number of flies.
Other flies which are annoying or dangerous are the punkies.
“This is another fly that is very aggressive, attacking man and domesticated animals wherever it can. It is well-named by our Indians the ‘no-see-um,’ it being so very small that it can only be felt, but not seen.
“It is a mere speck of matter, and it is difficult to understand how this small being can harbor the vast amount of cussedness it is known to possess. It is well equipped with a biting mouth, and those that have ever visited the northern lakes and woods know from experience that the insects know how to apply this tool.
“Whenever these flies light upon the hands and face they immediately insert this proboscis in the flesh, and judging from the burning sensation these bites cause, a large amount of poison must be injected at the same time. Where these tormenters abound the finest scenery loses its attraction, and the disappointed visitor leaves the spot with some forcible expressionsif not spoken with his lips, they are nevertheless thought.”
Horse flies, deer flies, etc., are among the larger members of the tribe. We know of several definite diseases which they spreadanthrax and tularemia, for instance.
The menace of the ordinary house flies in the spread of disease is so well known as hardly to need mention. “Swat the fly,” however, cannot be too often repeated.