Bug, the common name for hemipterous insects of the family Cimicidae, of which the best-known example is the house bug or bed bug (Cimex lectularius). This disgusting insect is of an oval shape, of a rusty red colour, and, in common with the whole tribe to which it belongs, gives off an offensive odour when touched; unlike the others, however, it is wingless. The bug is provided with a proboscis, which when at rest lies along the inferior side of the thorax, and through which it sucks the blood of man, the sole food of this species. It is nocturnal in its habits, remaining concealed by day in crevices of bed furniture, among the hangings, or behind the wall paper, and shows considerable activity in its nightly raids in search of food. The female deposits her eggs at the beginning of summer in crevices of wood and other retired situations, and in three weeks the young emerge as small, white, and almost transparent larvae. These change their skin very frequently during growth, and attain full development in about eleven weeks. Two centuries ago the bed bug was a rare insect in Britain, and probably owes its name, which is derived from a Celtic word signifying "ghost" or "goblin," to the terror which its attacks at first inspired.

An allied species, the dove-cote bug (Cimex columbaria), attacks domestic fowls and pigeons.