bug, common name correctly applied to insects belonging to the order Hemiptera, although members of the order Homoptera (e.g., mealybug) are sometimes referred to as bugs, as are other insects in general. The true bugs (Hemipterans) have a characteristic pair of front wings that are partially thickened and darkened at the base and partially membranous at the apex. Development is gradual through an incomplete metamorphosis with a number of nymphal stages before the reproductively mature adult stage is reached. Most bugs are terrestrial, but many are aquatic (e.g., various water bugs).
Although bugs vary greatly in size, color, and physical appearance, they all have piercing-sucking mouthparts in the form of a jointed beak. Most species suck plant juices (e.g., the squash bug and chinch bug); however, some suck the blood of other insects and spiders (e.g., the assassin bug and backswimmer). Others, such as the bedbug, feed on people and other animals. Many of these insects characteristically secrete defensive substances (e.g., the stink bug). The true bugs are classified in the phylum Arthropoda, class Insecta, order Hemiptera.