Classification

The present members of the order Hemiptera were historically placed into two orders, Homoptera and Heteroptera/Hemiptera, based on the differences in wing structure and the position of the rostrum. These two orders were then combined into the single order Hemiptera by many authorities, with Homoptera and Heteroptera classified as suborders.

The order is presently more usually divided into four or more suborders, after it was established that the families grouped together as "Homoptera" are not as closely related as had previously been thought (see paraphyly). Auchenorrhyncha contains the cicadas, leafhoppers, treehoppers, planthoppers, and froghoppers. The 12,500 species in the suborder Sternorrhyncha are the aphids, whiteflies and scale insects. The suborder Coleorrhyncha (comprising the single family Peloridiidae), contains fewer than 30 species of Gondwana-distributed bugs, and is sometimes grouped with the Heteroptera (to form the suborder Prosorrhyncha).

Heteroptera itself is a group of 25,000 species of relatively large bugs, including the shield bugs, seed bugs, assassin bugs, flower bugs, sweetpotato bugs and the water bugs. The closest relatives of hemipterans are the thrips and lice, which collectively form the "hemipteroid assemblage" within the Exopterygota subclass of the Class Insecta.

The fossil record of hemipterans goes back to the Early Permian. Homopterans appeared first, with Heteroptera first appearing in the Triassic.