Fig. 27—Blue-bottle fly (Lucilia sericata).
Fig. 28—Flesh-fly (Sarcophaga sp).
Fig. 29—"The little house-fly" (Homalomyia canicularis). | Fig. 30—Horse bot-fly (Gastrophilus equi) |
Fig. 31—Ox warble-fly (Hypoderma lineata). | Fig. 32—Sheep bot-fly (Gastrophilus nasalis). |
The bot-flies of cattle or the oxwarbles ([Fig. 31]) gain an entrance into the alimentary canal in the same way, that is, by the eggs being licked from the hairs on the body where they have been laid by the adult fly. But instead of passing on into the stomach they collect in the esophagus and later make their way through the walls of this organ and through the tissues of the body until they at last reach a place along the back just under the skin. Here as they are completing their development they make more or less serious sores on the backs of the infested animals. The hides on such animals are rendered nearly valueless by the holes made by the larvæ. When fully mature they drop to the ground and complete their transformations.
The sheep bot-flies ([Fig. 32]) lay their eggs in the nostrils of sheep. The larvæ pass up into the frontal sinuses where they feed on the mucus, causing great suffering and loss. Many other species of animals are infested with their own particular species of bots. Several instances are recorded where the oxwarble has occurred in man, always causing much suffering and sometimes death.
One or more species of bot-flies occurring in the tropical parts of America frequently attack man. The early larval stage soon after it has entered the skin is known as the Ver macaque. Later stages as torcel or Berne. The presence of the larvæ produces very painful and troublesome sores. It is supposed that the adult flies (one species of which is Dermatobia cyaniventris) lay their eggs on the skin which the larvæ penetrate as soon as they hatch. It has also been suggested that they might reach the subcutaneous tissue by migrating from the alimentary canal as do some of the other bot-flies. A very serious eye disease, Egyptian opthalmia, is known to be spread by the house-flies and others. These flies are often abundant about the eyes, especially of children suffering from this disease. It is suspected that certain small flies (Oscinidæ) in the southern part of the United States are responsible for the spread of disease known as "sore eye."