[The members of this genus which occur in temperate and tropical countries are provided with a hard, slender, shiny black proboscis which projects horizontally from beneath the head; by means of this structure they can bite severely. In general appearance they resemble house flies, but the proboscis at once distinguishes them. In many parts of Britain they are known as storm flies on account of their frequent appearance indoors previous to a storm of rain or wind, which I have invariably found to be correct; they are also called stinging flies. In colour they are greyish, dusky or brownish-grey or black, varying from 5 to 7 mm. in length; the thorax has dark longitudinal stripes and the abdomen dark spots or bands. In the male the eyes are closer together than in the female. These flies usually occur in stables and farmyards, along woods and in lanes, and mainly attack mammals.

[One species (Stomoxys calcitrans, Linnæus) occurs practically all over the world. The female lays her eggs in moist, warm, decaying vegetation; as many as eighty may be laid by a single female. The ova are white, banana-shaped, with a broad groove on the shorter curvature; they may hatch in two or three days. The creamy-white larva tapers to a point at the head end, and is truncated at the tail end. Two black mouth hooks are plainly visible at the cephalic extremity. There are two plates on the posterior surface of the last segment which bear the respiratory pores, nearly circular in outline. It reaches maturity in fourteen to twenty-one days; when mature it is 11 mm. long. The pupal stage is passed in the old larva skin and lasts from nine to thirteen days; it is barrel-shaped, 5 to 8 mm. long, and of a bright reddish-brown to dark chestnut-brown colour.

[This insect may act as a carrier of anthrax, and has been proved to be the agent of an extensive epidemic of malignant pustule in the Isle of Pines, New Caledonia.425

[Noè’s426 experiments tend to show that it is an intermediate host and transmitter of Filaria labiato-papillosa of the ox.

[Surra is generally stated to be transmitted by Stomoxys as well as Tabanus, and yet Nitzman in the Philippines obtained uniformly negative results in exhaustive experiments. Others have also been unsuccessful. Certainly Stomoxys can transmit the disease in French West Africa (Bonet and Roubaud), and mechanically has been proved to be capable of disseminating other trypanosomes (experimentally): sleeping sickness (T. gambiense); nagana (T. brucei); souma (T. cazalboui); and el debat (T. soudanense).

[S. calcitrans may also be a carrier of poliomyelitis (Rosenau and Brues, Harvard Alumni Bulletin, 1912, xv, No. 9, pp. 140–142). Several species are now known (S. brunnipes, Grünb.; S. inornata, Grünb.; S. nigra, Macq.; S. omega, Newst.; S. ochrosoma, Speiser, etc.).

[A genus of small flies which bite man and animals, but are not so far connected with the transmission of any disease in man, but in Java it appears to carry surra (P. Schat, Meeledeel Praefstation Oost-Java, 1903, 3e ser., No. 44), the species being Lyperosia exigua, Meijere. These flies can be told from Stomoxys by the palpi being broader, flattened laterally, and as long, or nearly so, as the proboscis. When not feeding the palpi enclose the proboscis, as in Glossina. They are usually about half the size of Stomoxys, and are the smallest blood-sucking Muscidæ. They frequently swarm around and upon domesticated animals.

[The life-history of the horn fly in America (L. irritans, Linn.) is well known. It lays its ova singly in freshly dropped cow-dung, and there the maggots feed, pupating in the soil beneath.

[Patton and Cragg also give some details as to the life-history of Liperosia exigua (“Medical Entomology,” p. 375) as follows: “L. exigua, whose habits have been observed in Madras, usually lays twelve eggs at a time. The flies immediately return to the cow and the process is repeated when the dung is again dropped. The larvæ migrate from the dung when about to pupate, and the puparia are always found in the earth at some distance away or under the sides of the patch of dung. The fly usually hatches out in five days, though sometimes as late as the eighth. Weiss has studied the life-history of irritans var. weisii from Algeria; its larval stage lasts five days, and the flies hatch out of the puparia in another five days.”

[The other biting genera of Muscidæ, Hæmatobia, Hæmatobosca, Bdellolarynx, Stygeromyia, and Philæmatomyia, although sometimes annoying to man, have not in any way been connected with any disease.

[The horse fly (Hæmatobia irritans, L.427) attacks cattle chiefly, but now and then man is bitten. The different species can be told from Stomoxys by the palpi being nearly as long as the proboscis.

[The genus Philæmatomyia, Austen, is intermediate between Stomoxys and Musca in structure, and between the non-blood-sucking Musca, as M. domestica, and the blood-sucking Musca pattoni, Austen, which feeds on the blood exuding from the bites of true blood-suckers. They occur in Central Africa and India, Ceylon and Cyprus (vide “The Life-history of Philæmatomyia insignis, Austen,” Ann. Trop. Med. and Par., 1912, v, p. 515).

[Two flies belonging to the family Anthomyidæ also attack man, namely:—

[Hydrotæa meteorica, L. (the meteoric fly). This fly attacks man as well as animals. They especially bite around the eyes and nostrils of animals, but are not so particular with man; the head, however, is usually chosen. Linnæus called it the meteoric fly because it often forms clouds around horses’ heads at the approach of rain. The Hydrotæas are usually black or blue-black in colour with bare eyes and simple abdomen, the front femora peculiarly constructed. H. meteorica, L., occurs in Britain.

[The members of the genus Hydrophoria, Desvoidy, also bite man.

[The Pupipara are all blood-suckers, the majority occurring as parasites on mammals and birds, where they are more or less permanent parasites. Occasionally some may attack man. They all produce their young fully formed, and they assume the pupal stage immediately after extrusion. The puparia are large. They are mostly flat, louse-like flies which may or may not be winged. In the case of Melophagus I have found the puparia are often passed by the female. The winged forms have a short quick flight, and when disturbed will seek shelter in man’s hair or beard. Two main families occur: (1) the Hippoboscidæ, and (2) the Nycteribiidæ. The former occur on animals and birds, the latter on bats only, but may invade man. Two other families are known—the Braulidæ (bee parasites) and the Streblidæ (bat parasites).

[The mouth of the Hippoboscidæ is long and sharp, forming a proboscis. The thorax and abdomen are flat and leathery. The legs are stout and strong, and terminate in large dentate claws and other structures of use in holding on to the hair or feathers of their host when blood-sucking.

[Austen says it is probable that the Hippoboscidæ are descended from ancestors belonging to the Muscidæ, which underwent modification in bodily structure as the consequence of the adoption of a parasitic mode of life.

[Two wings are present in the true Hippoboscæ, Hippobosca equina (of the horse), H. camelina (of the camel), H. maculata (of oxen), and H. capensis (of dogs), but are absent in Melophagus, the sheep tick or ked fly (M. ovinus).

[In two genera, Lipoptena and Echestypus, wings are at first present, but are lost as soon as the fly finds its permanent host.

[With regard to their biting man, such is only occasional. I have known sheep shearers to be badly bitten by Melophagus ovinus, and have more than once been attacked myself when standing where shearing is taking place. Sharp records the grouse parasite, Ornithomyia lagopodis, as once biting severely a gamekeeper in Scotland. There are also records of H. maculata biting man in Africa and India.

[Although so far not connected with any human disease, it is interesting to note Theiler has shown that Hippobosca rufipes, v. Olfers, and H. maculata, Leach, are capable of transmitting Trypanosoma theileri, Laveran, the cause of gall sickness amongst cattle in the Transvaal. It is now considered, however, that Trypanosoma theileri is non-pathogenic, and that the cause of gall sickness is a piroplasma-like organism known as Anaplasma marginale. Theiler, Laveran and Mesnil all hold this view (vide Laveran and Mesnil, “Trypanosomes and Trypanosomiases,” second edition, 1912, p. 330).

[Lynchia.—Three members of this genus have been shown to transmit the non-pathogenic (?) organism, Hæmoproteus columbæ amongst pigeons in Algeria and S. America.

[In a recent number of the Journal of Economic Entomology,428 Brues and Sheppard point out the possibility of acute epidemic poliomyelitis (infantile paralysis) being an insect-borne disease. They summarize as follows:—

[Many facts connected with the distribution of cases and the spread of epidemics of this disease with histories of insects bites, suggest at least that the disease may be insect-borne. Field work during the past summer, together with a consideration of the epidemiology of the disease so far known, points strongly towards biting flies as possible carriers of the virus. It seems probable that the common stable fly (Stomoxys calcitrans, L.) may be responsible to a certain extent for the spread of acute epidemic poliomyelitis, possibly aided by other biting flies such as Tabanus lineola. No facts which disprove such a hypothesis have as yet been adduced, and experiments based upon it are now in progress.

[If the disease should prove to be common to any species of domestic animals, as is now strongly suspected, a secondary connection of ticks in spreading the disease among such animals seems probable, as has been mentioned.