A bug is an insect of the order Hemiptera, known
as the true bugs, comprising around 50,000–80,000 species
of cicadas, aphids, planthoppers, leafhoppers, shield bugs,
and others. 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 and sucking out the liquids — typically sap.