Several families of the true bugs include forms which, while normally inoffensive, are capable of inflicting painful wounds on man. In these, as in all of the Hemiptera, the mouth-parts are modified to form an organ for piercing and sucking.

The upper lip, or labrum, is much reduced and immovable, the lower lip, or labium, is elongated to form a jointed sheath, within which the lance-like mandibles and maxillæ are enclosed. The mandibles are more or less deeply serrated, depending on the species concerned.