Larvæ in fungi, but occasionally also on larvæ of butterflies and Hymenoptera; occasionally introduced into the human intestine (Joseph).
Musca domestica, L.,
and M. (Calliphora) vomitoria, L., and allied species; larvæ of these have been repeatedly found in the intestine and nose of man (Mankiewicz, etc.).[411]
Musca domestica, Linn. (Common House-fly).
It is not only on account of a few larvæ of the common house-fly (Musca domestica) being found in the intestines of man that it is of importance medically. It is far more important on account of the part it plays in the spread of diseases of the intestines, such as typhoid fever and cholera, infantile diarrhœa and dysentery.
Howard and Clark (Journ. Exp. Med., 1912, xvi, No. 6, pp. 850–859) have shown that the house-fly is capable of carrying the virus of poliomyelitis for several days on the surface of the body and for several hours in the gastro-intestinal tract. The house-fly may also distribute the ova of Tænia solium and the white worms (Oxyuris and Ascaris). It has also been proved that they may carry the germs of tuberculosis, and it is said that they play an important part in the spread of infectious ophthalmia in Egypt.
This insect is found in all parts of the world. In warm countries it breeds all the year round, and it may do so even in temperate climates in warm places, such as stove houses. Most, however, die off in the autumn; but some survive the winter as adults, in such places as kitchens, restaurants, and warm houses. I have never failed to find a few Musca domestica in houses during the winter. The majority, however, hibernate as puparia.
The females deposit from 120 to 150 eggs in a batch in stable manure, rotting vegetation, house refuse, spent hops, old soiled bedding, etc. A single female may lay as many as six batches of ova during her life. The eggs are shiny white, and hatch in from eight to twenty-four hours in warm weather to three or four days in cool weather. The white footless maggots are cylindrical, tapering to a point at the head end, truncated posteriorly. The head consists of two dark mandibular hooks and two short antennæ. On the tail end are two plates, the stigmata, in which the main tracheal trunks open; in the second segment are a small pair of projecting stigmata. The larval stage lasts from seven to five days in hot weather; but in cold weather in temperate climes it may last six or eight weeks.
The larva on reaching maturity becomes a barrel-shaped puparium of a dark brown to black colour, and in this case changes to the pupa. This stage lasts from three days in the tropics to four or five weeks in cold weather, the life cycle thus varying from ten days in the tropics to fourteen in warm weather in Europe up to three or four months under unfavourable conditions.