Handbook of Medical Entomology Part 12

There are even well authenticated accounts on record of death of humans from the attacks of large swarms of these gnats. In some regions, and especially in the Mississippi Valley in this country, certain species of black flies have been the cause of enormous losses to farmers and stockmen, through their attacks on poultry and domestic animals. C. V.

Riley states that in 1874 the loss occasioned in one county in Tennessee was estimated at $500,000.

The measures of prevention and protection against these insects have been well summarized by Forbes (1912). They are of two kinds: "the use of repellents intended to drive away the winged flies, and measures for the local destruction of the aquatic larvae. The repellents used are either smudges, or surface applications made to keep the flies from biting. The black-fly will not endure a dense smoke, and the well-known mosquito smudge seems to be ordinarily sufficient for the protection of man. In the South, leather, cloth, and other materials which will make the densest and most stifling smoke, are often preserved for this use in the spring. Smudges are built in pastures for the protection of stock, and are kept burning before the doors of barns and stables. As the black-flies do not readily enter a dark room, light is excluded from stables as much as possible during the gnat season. If teams must be used in the open field while gnats are abroad, they may be protected against the attacks of the gnats by applying cotton-seed oil or axle grease to the surface, especially to the less hairy parts of the animals, at least twice a day. A mixture of oil and tar and, indeed, several other preventives, are of practical use in badly infested regions; but no definite test or exact comparison has been made with any them in a way to give a record of the precise results."

"It is easy to drive the flies from houses or tents by burning pyrethrum powder inside; this either kills the flies or stupifies them so that they do not bite for some time thereafter." * * * "Oil of tar is commonly applied to the exposed parts of the body for the purpose of repelling the insects, and this preparation is supplied by the Hudson Bay Company to its employees. Minnesota fishermen frequently grease their faces and hands with a mixture of kerosene and mutton tallow for the same purpose." We have found a mixture of equal parts of kerosene and oil of pennyroyal efficient.

Under most circ.u.mstances very little can be done to destroy this insect in its early stage, but occasionally conditions are such that a larvicide can be used effectively. Weed (1904), and Sanderson (1910) both report excellent results from the use of phinotas oil, a proprietary compound. The first-mentioned also found that in some places the larvae could be removed by sweeping them loose in ma.s.ses with stiff stable brooms and then catching them downstream on wire netting stretched in the water.

Chironomidae or Midges

The flies of this family, commonly known as midges, resemble mosquitoes in form and size but are usually more delicate, and the wing-veins, though sometimes hairy, are not fringed with scales. The venation is simpler than in the mosquitoes and the veins are usually less distinct.

These midges, especially in spring or autumn, are often seen in immense swarms arising like smoke over swamps and producing a humming noise which can be heard for a considerable distance. At these seasons they are frequently to be found upon the windows of dwellings, where they are often mistaken for mosquitoes.

The larvae are worm-like, but vary somewhat in form in the different genera. Most of them are aquatic, but a few live in the earth, in manure, decaying wood, under bark, or in the sap of trees, especially in the sap which collects in wounds.

[Ill.u.s.tration: 77. Culicoides guttipennis; (_a_) adult, (15); (_b_) head of same; (_c_) larva; (_d_) head; (_e_) pupa. After Pratt.]

Of the many species of CHIRONOMIDae, (over eight hundred known), the vast majority are inoffensive. The sub-family Ceratopogoninae, however, forms an exception, for some of the members of this group, known as sandflies, or punkies, suck blood and are particularly troublesome in the mountains, along streams, and at the seash.o.r.e. Most of these have been cla.s.sed under the genus _Ceratopogon_, but the group has been broken up into a number of genera and _Ceratopogon_, in the strict sense, is not known to contain any species which sucks the blood of vertebrates.

THE CERATOPOGONINae--The Ceratopogoninae are among the smallest of the Diptera, many of them being hardly a millimeter long and some not even so large. They are Chironomidae in which the thorax is not prolonged over the head. The antennae are filiform with fourteen (rarely thirteen) segments in both s.e.xes, those of the male being brush-like. The basal segment is enlarged, the last segment never longer than the two preceding combined, while the last five are sub-equal to, or longer than the preceding segment. The legs are relatively stouter than in the other Chironomidae. The following three genera of this subfamily are best known as blood suckers in this country.

Of the genus _Culicoides_ there are many species occurring in various parts of the world. A number are known to bite man and animals and it is probable that all are capable of inflicting injury. In some localities they are called punkies, in others, sand-flies, a name sometimes also applied to the species of _Simulium_ and _Phlebotomus_. Owing to their very small size they are known by some tribes of Indians as No-see-ums.

The larvae are found in ponds, pools, water standing in hollow tree stumps, and the like. Though probably living chiefly in fresh water, we have found a species occurring in salt water. The larvae are small, slender, legless, worm-like creatures (fig. 77_c_) with small brown head and twelve body segments. The pupae (fig. 77_e_) are slender, more swollen at the anterior end and terminating in a forked process. They float nearly motionless in a vertical position, the respiratory tubes in contact with the surface film. The adults are all small, rarely exceeding 2 mm. in length. The wings are more or less covered with erect setulae or hairs and in many species variously spotted and marked with iridescent blotches. The antennae have fourteen segments, the palpi usually five. The wing venation and mouth-parts are shown in figures 77 and 78. Of the twenty or more species of this genus occurring in the United States the following are known to bite: _C. cinctus_, _C.

guttipennis_, _C. sanguisuga_, _C. stellifer_, _C. variipennis_, _C.

unicolor_.

[Ill.u.s.tration: 78. Culicoides guttipennis; mouth parts of adult. After Pratt.]

One of the most widely distributed and commonest species in the Eastern States is _C. guttipennis_ (fig. 77a). It is black with brown legs, a whitish ring before the apex of each femur and both ends of each tibia; tarsi yellow, k.n.o.bs of halteres yellow. Mesonotum opaque, brown, two vittae in the middle, enlarging into a large spot on the posterior half, also a curved row of three spots in front of each wing, and the narrow lateral margins, light gray pruinose. Wings nearly wholly covered with brown hairs, gray, with markings as shown in the figure. Length one mm.

_Johannseniella_ Will. is a wide-spread genus related to the foregoing.

Its mouth-parts are well adapted for piercing and it is said to be a persistent blood sucker, particularly in Greenland. This genus is distinguished from _Culicoides_ by its bare wings, the venation (fig.

163, c), and the longer tarsal claws. There are over twenty North American species.

[Ill.u.s.tration: 79. Chrysops univittatus, (4). After Osborn.]

In the Southwestern United States, _Tersesthes torrens_ Towns. occurs, a little gnat which annoys horses, and perhaps man also, by its bite. It is related to _Culicoides_ but differs in the number of antennal segments and in its wing venation (fig. 163, e). The fly measures but two mm. in length and is blackish in color. The antennae of the female have thirteen segments, the palpi but three, of which the second is enlarged and swollen.

Tabanidae or Horse-Flies

The TABANIDae,--horse-flies, ear-flies, and deer-flies,--are well-known pests of cattle and horses and are often extremely annoying to man. The characteristics of the family and of the princ.i.p.al North American genera are given in the keys of Chapter XII. There are over 2500 recorded species. As in the mosquitoes, the females alone are blood suckers. The males are flower feeders or live on plant juices. This is apparently true also of the females of some of the genera.

The eggs are deposited in ma.s.ses on water plants or gra.s.ses and sedges growing in marshy or wet ground. Those of a common species of _Taba.n.u.s_ are ill.u.s.trated in figure 80, _a_. They are placed in ma.s.ses of several hundred, light colored when first deposited but turning black. In a week or so the cylindrical larvae, tapering at both ends (fig. 80, _b_), escape to the water, or damp earth, and lead an active, carnivorous life, feeding mainly on insect larvae, and worms. In the forms which have been best studied the larval life is a long one, lasting for months or even for more than a year. Until recently, little was known concerning the life-histories of this group, but the studies of Hart (1895), and Hine (1903 +) have added greatly to the knowledge concerning North American forms.

Many of the species attack man with avidity and are able to inflict painful bites, which may smart for hours. In some instances the wound is so considerable that blood will continue to flow after the fly has left.

We have seen several cases of secondary infection following such bites.

[Ill.u.s.tration: 80. (_a_) Eggs of Taba.n.u.s. Photograph by J. T. Lloyd.]

[Ill.u.s.tration: 80. (_b_) Larva of Taba.n.u.s. Photograph by M. V. S.]

The horse-flies have been definitely convicted of transferring the trypanosome of surra from diseased to healthy animals and there is good evidence that they transfer anthrax. The possibility of their being important agents in the conveyal of human diseases should not be overlooked. Indeed, Leiper has recently determined that a species of _Chrysops_ transfers the blood parasite _Filaria diurna_.

Leptidae or Snipe-Flies

The family LEPTIDae is made up of moderate or large sized flies, predaceous in habit. They are sufficiently characterized in the keys of Chapter XII. Four blood-sucking species belonging to three genera have been reported. Of these _Symphoromyia pachyceras_ is a western species.

Dr. J. C. Bradley, from personal experience, reports it as a vicious biter.

[Ill.u.s.tration: 80. (_c_) Mouth parts of Taba.n.u.s. After Grunberg.]

Oestridae or Bot-flies

To the family OESTRIDae belong the bot and warble-flies so frequently injurious to animals. The adults are large, or of medium size, heavy bodied, rather hairy, and usually resemble bees in appearance.

The larvae live parasitically in various parts of the body of mammals, such as the stomach (horse bot-fly), the subcutaneous connective tissue (warble-fly of cattle), or the nasal pa.s.sage (sheep bot-fly or head maggot).

There are on record many cases of the occurrence of the larvae of Oestridae as occasional parasites of man. A number of these have been collected and reviewed in a thesis by Mme. Petrovskaia (1910). The majority of them relate to the following species.

_Gastrophilus haemorrhoidalis_, the red tailed bot-fly, is one of the species whose larvae are most commonly found in the stomach of the horse.

Schoch (1877) cites the case of a woman who suffered from a severe case of chronic catarrh of the stomach, and who vomited, and also pa.s.sed from the a.n.u.s, larvae which apparently belonged to this species. Such cases are exceedingly rare but instances of subcutaneous infestation are fairly numerous. In the latter type these larvae are sometimes the cause of the peculiar "creeping myasis." This is characterized at its beginning by a very painful swelling which gradually migrates, producing a narrow raised line four to twenty-five millimeters broad. When the larva is mature, sometimes after several months, it becomes stationary and a tumor is formed which opens and discharges the larva along with pus and serum.

_Gastrophilus equi_ is the most widespread and common of the horse bot-flies. Portschinsky reports it as commonly causing subcutaneous myasis of man in Russia.

_Hypoderma bovis_ (= _Oestrus bovis_), and _Hypoderma lineata_ are the so-called warble-flies of cattle. The latter species is the more common in North America but Dr. C. G. Hewitt has recently shown that _H. bovis_ also occurs. Though warbles are very common in cattle in this country, the adult flies are very rarely seen. They are about half an inch in length, very hairy, dark, and closely resemble common honey-bees.

They deposit their eggs on the hairs of cattle and the animals in licking themselves take in the young larvae. These pa.s.s out through the walls of the sophagus and migrate through the tissues of the animal, to finally settle down in the subcutaneous tissue of the back. The possibility of their entering directly through the skin, especially in case of infestation of man, is not absolutely precluded, although it is doubtful.

For both species of _Hypoderma_ there are numerous cases on record of their occurrence in man. Hamilton (1893) saw a boy, six years of age, who had been suffering for some months from the glands on one side of his neck being swollen and from a fetid ulceration around the back teeth of the lower jaw of the same side. Three months' treatment was of no avail and the end seemed near; one day a white object, which was seen to move, was observed in the ulcer at the root of the tongue, and on being extracted was recognized as a full grown larva of _Hypoderma_. It was of usual tawny color, about half an inch long when contracted, about one third that thickness, and quite lively. The case resulted fatally. The boy had been on a dairy farm the previous fall, where probably the egg (or larva) was in some way taken into his mouth, and the larva found between the base of the tongue and the jaw suitable tissue in which to develop.

Topsent (1901) reports a case of "creeping myasis" caused by _H.

lineata_ in the skin of the neck and shoulders of a girl eight years of age. The larva travelled a distance of nearly six and a half inches. The little patient suffered excruciating pain in the place occupied by the larva.

_Hypoderma diana_ infests deer, and has been known to occur in man.

_Oestris ovis_, the sheep bot-fly, or head maggot, is widely distributed in all parts of the world. In mid-summer the flies deposit living maggots in the nostrils of sheep. These larvae promptly pa.s.s up the nasal pa.s.sages into the frontal and maxillary sinuses, where they feed on the mucous to be found there. In their migrations they cause great irritation to their host, and when present in numbers may cause vertigo, paroxysms, and even death. Portschinsky in an important monograph on this species, has discussed in detail its relation to man. He shows that it is not uncommon for the fly to attack man and that the minute living larvae are deposited in the eyes, nostrils, lips, or mouth. A typical case in which the larvae were deposited in the eye was described by a German oculist Kayser, in 1905. A woman brought her six year old daughter to him and said that the day before, about noontime, a flying insect struck the eye of the child and that since then she had felt a pain which increased towards evening. In the morning the pain ceased but the eye was very red. She was examined at about noon, at which time she was quiet and felt no pain. She was not sensitive to light, and the only thing noticed was a slight congestion and acc.u.mulation of secretion in the corner of the right eye. A careful examination of the eye disclosed small, active, white larvae that crawled out from the folds of the conjunctiva and then back and disappeared. Five of these larvae were removed and although an uncomfortable feeling persisted for a while, the eye became normal in about three weeks.

Some of the other recorded cases have not resulted so favorably, for the eyesight has been seriously affected or even lost.

According to Edmund and Etienne Sergent (1907), myasis caused by the larvae of _Oestris ovis_ is very common among the shepherds in Algeria.

The natives say that the fly deposits its larvae quickly, while on the wing, without pause. The greatest pain is caused when these larvae establish themselves in the nasal cavities. They then produce severe frontal headaches, making sleep impossible. This is accompanied by continuous secretion from the nasal cavities and itching pains in the sinuses. If the larvae happen to get into the mouth, the throat becomes inflamed, swallowing is painful, and sometimes vomiting results. The diseased condition may last for from three to ten days or in the case of nasal infection, longer, but recovery always follows. The natives remove the larvae from the eye mechanically by means of a small rag. When the nose is infested, tobacco fumigations are applied, and in case of throat infestation gargles of pepper, onion, or garlic extracts are used.

_Rhinstrus nasalis_, the Russian gad-fly, parasitizes the nasopharyngeal region of the horse. According to Portschinsky, it not infrequently attacks man and then, in all the known cases deposits its larvae in the eye, only. This is generally done while the person is quiet, but not during sleep. The fly strikes without stopping and deposits its larva instantaneously. Immediately after, the victim experiences lancinating pains which without intermission increase in violence. There is an intense conjunctivitis and if the larvae are not removed promptly the envelopes of the eye are gradually destroyed and the organ lost.

[Ill.u.s.tration: 81. Larvae of Dermatobia cyaniventris. After Blanchard.]