Shield bug and stink bug (or shieldbug and stinkbug) are common names applied to various insects of the Hemiptera order (the "true bugs"), in the Heteroptera suborder. Shield bugs have glands in their thorax between the first and second pair of legs which produce a foul smelling liquid. This liquid is used defensively to deter potential predators and is sometimes released when the bugs are handled carelessly. The stink comes from aldehydes such as CH3–(CH2)2–CH=CH–CHO, and is chemically similar to pheromones.
The nymphs, similar to adults except smaller and without wings, also have stink glands.
The nymphs and adults have piercing mouthparts which most use to suck sap from plants, although some eat other insects. When they group in large numbers they can become significant pests.
The superfamily Pentatomoidea consists of generally shield-shaped true bugs, with the families listed to the right.
Other species that resemble shield bugs are found in the Coreoidea superfamily.