6. The little house fly (_Homalomyia brevis_): Adults and larva 9 7. The fruit fly (_Drosophila ampelophila_): Adult, larva, puparium, and details. 10 8. The dung fly (_Sepsis violacea_): Adult, puparium, and details 11 9. The house centipede (_Scutigera forceps_): Adult 14 HOUSE FLIES. INTRODUCTION. There are several species of flies which are commonly found in houses, although but one of these should be called the house fly proper. This is the _Musca domestica_ L. (fig. 1 ) and is a medium-sized, grayish fly, with its mouth parts spread out at the tip for sucking up liquid substances. It is found in nearly all parts of the world. On account of the conformation of its mouth parts, the house fly can not bite, yet no impression is stronger in the minds of most people than that this insect does occasionally bite. This impression is due to the frequent occurrence in houses of another fly (_Stomoxys calcitrans_ L.) (fig. 2), which is called the stable fly, and which, while closely resembling the house fly (so closely, in fact, as to deceive anyone but an entomologist), differs from it in the important particular that its mouth parts are formed for piercing the skin. It is perhaps second in point of abundance to the house fly in most portions of the Northeastern States. It breeds in horse manure, cow manure, and in warm decaying vegetation like old straw and grass heaps. [Illustration: Fig. 1.--The common house fly (_Musca domestica_): Puparium at left; adult next; larva and enlarged parts at right. All enlarged. (Author's Illustration.)] A third species, commonly called the cluster fly (_Pollenia rudis_ Fab.), is a very frequent visitant of houses, particularly in the spring and fall. This fly is somewhat larger than the house fly, with a dark-colored, smooth abdomen and a sprinkling of yellowish hairs. It is not so active as the house fly and, particularly in the fall, is very sluggish. At such times it may be picked up readily and is very subject to the attacks of a fungous disease which causes it to die upon window panes, surrounded by a whitish efflorescence. Occasionally this fly occurs in houses in such numbers as to cause great annoyance, but such occurrences are comparatively rare. It is said in its earlier stages to be parasitic on certain angleworms. A fourth species is another stable fly, known as _Muscina stabulans_ Fall. (fig. 3), a form which almost exactly resembles the house fly in general appearance, and which does not bite as does the biting stable fly. It breeds in decaying vegetable matter and in excrement. [Illustration: Fig. 2.--The stable fly or biting house fly (_Stomoxys calcitrans_): Adult, larva, puparium, and details. All enlarged. (Author's illustration.)]