HOUSE-FLY, Mama domestica, an insect too well known to need description, and remarkable for its extensive distribution both in the old and in the new world. It belongs to the vast dipterous family muscides. The maggots live in moist dung, in a rotting vegetables, etc. When house-flies become annoying, various expedients are resorted to for killing them, as trapping in glasses partially tilled with some sweet viscid. fluid, or by pieces of paper covered with a mixture of sweet and poisonous sub stances. Sweet substances, however, attract flies into a room, so that the benefit of fly traps is often doubtful; and care must be taken that the poisons used do not endanger the lives of children or others. Quassia is safe enough in this respect, and very fatal to flies.
In addition to what has been said in the article DIPTERA concerning the power which many insects possess of walking on perpendicular walls, ceilings, etc., it may here be mentioned that, according to the observations of Mr. Hepworth, who has care= fully investigated this subject, although the membranous disks (pulvillt) on the foot of a fly are incapable of being used as suckers, yet the hairs with which they are thickly beset are terminated by minute disks, which probably are so used. At the same time,
these minute disks appear to exude a liquid, not viscid, which probably serves to make: the adhesion more perfect.
The proboscis of the house-fly is a very interesting microscopic object. It is chiefly formed by an extraordinary development of tongtiviet or ligula, the upper part of the under-lip (labium), but with this are combined lancets formed of the metamorphosed madike. (For these, see COLEOPTERA.) The lobes of the ligula are much enlarged and fleshy. They are surrounded by rough hairs, to aid in scraping or tearing delicate sin• flfces. There are many rows ofthese hairs on each lobe. In using its proboscis to feed on dry substances, as sugar, the fly moistens them with a liquid which may be regarded as saliva, so as to fit them for suctorial action. To aid in this suctorial action, the muscles of the lobes of the ligula are disposed in a spiral form.