Shiel 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.