Several species of metallic greenish or bluish flies are also occasionally found in houses, the most abundant of which is the so-called blue-bottle fly (_Calliphora erythrocephala_ Meig.). This insect is also called the blow-fly or meat-fly and breeds in decaying animal material. A smaller species, which may be called the small blue-bottle fly, is _Phormia terrænovæ_ Desv. (fig. 4); and a third, which is green or blue in color and a trifle smaller than the large blue-bottle, is _Lucilia cæsar_ L. (fig. 5). There is still another species, smaller than any of those so far mentioned, which is known to entomologists as _Homalomyia canicularis_ L., sometimes called the small house fly. A related species, _H. brevis_ Rond., is shown in figure 6. _H. canicularis_ is distinguished from the ordinary house fly by its paler and more pointed body and conical shape. The male, which is much commoner than 'the female, has large pale patches at the base of the abdomen, which are translucent when the fly is seen on a window pane. It is this species that is largely responsible for the prevalent idea that flies grow after gaining wings. Most people think that these little Homalomyias are the young of the larger flies, which, of course, is distinctly not the case. They breed in decaying vegetable material, in the excreta of animals, and in dead insects. Still another fly, and this one is still smaller, is a jet-black species known as the window fly (_Scenopinus fenestralis_ L.), which in fact has become more abundant of later years. Its larva is a white, very slender, almost thread-like creature, and is found in cracks of the floor in buildings, where it feeds on other small insects. In the autumn, when fruit appears on the sideboard, many specimens of a small fruit-fly (_Drosophila ampelophila_ Loew) (fig. 7) make their appearance, attracted by the odor of overripe fruit. A small, slender fly is not infrequently seen in houses, especially upon window panes. This is _Sepsis violacea_ Meig., shown enlarged in figure 8. [Illustration: Fig. 3.--A stable fly (_Muscina stabulans_): Adult, larva, and details. All enlarged. (Author's Illustration.)] All of these species, however, are greatly dwarfed in numbers by the common house fly. In 1900 the writer made collections of the flies in dining rooms in different parts of the country, and out of a total of 23,087 flies 22,808 were _Musca domestica_--that is, 98.8 per cent of the whole number captured. The remainder, consisting of 1.2 per cent of the whole, comprised various species, including those mentioned above. LIFE HISTORY OF THE TRUE HOUSE FLY.