Characteristics

The defining feature of hemipterans is their possession of mouthparts where the mandibles and maxillae have evolved into a proboscis, sheathed within a modified labium to form a "beak" or "rostrum" which is capable of piercing tissues (usually plant tissues) and sucking out the liquids — typically sap.

The wings of Hemiptera are either entirely membranous such as in the Sternorrhyncha and Auchenorrhyncha or in the form of hemelytra in the Heteroptera. Hemelytra refers to the partially hardened forewings, usually the anterior portion or the corium. The hindwings of Heteroptera are membranous.

The antennae in Hemiptera are typically five-segmented, although they can still be quite long, and the tarsi of the legs are three-segmented or shorter.

Although hemipterans vary widely in their overall form, their mouthparts (formed into a "rostrum") are quite distinctive; the only orders with mouthparts modified in a similar manner are the Thysanoptera and some Phthiraptera, and these are generally easy to recognize as non-hemipteran for other reasons. Aside from the mouthparts, various insects can be confused with hemipterans, including cockroaches and psocids, both of which have longer many-segmented antennae, and some beetles, but these have fully hardened forewings which do not overlap.