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 forewings of Hemiptera are either entirely membranous, as in the Sternorrhyncha and Auchenorrhyncha, or partially hardened, as in most Heteroptera. The name "Hemiptera" is from the Greek ἡμι- (hemi; "half") and πτερόν (pteron; "wing"), referring to the forewings of many heteropterans which are hardened near the base, but membranous at the ends. Wings modified in this manner are termed hemelytra (singular: hemelytron), by analogy with the completely hardened elytra of beetles, and occur only in the suborder Heteroptera. The forewings may be held "roofwise" over the body (typical of Sternorrhyncha and Auchenorrhyncha), or held flat on the back, with the ends overlapping (typical of Heteroptera). In all suborders, the hindwings – if present at all – are entirely membranous and usually shorter than the forewings.
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.
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