There is only one character which groups all hemipterans - the sucking and piercing mouthparts in the form of a long proboscis or rostrum. It encloses four stylets. The two outer stylets have serrated teeth to pierce tissues. The inner ones have a groove alongside it which fits perfectly forming two channels, one for saliva and the other one for digested food.
This order is divided into four suborders:
Coleorrhyncha the most primitive with characteristics of both heteropterans and homopterans. Today it is considered to be more closely related to Heteroptera
Heteroptera (the rostrum extends from the anterior part of the head, it may be curved and directed downwards or forwards. Wings stay flat on the body)
Auchenorrhyncha (the rostrum extends from the posterior part of the head and is always directed backwards. Wings stay like a roof)
Sternorrhyncha (the rostrum extends almost from the anterior legs and is always directed backwards)
Coleorrhyncha, Auchenorrhynca y Sternorrhyncha formed the former Suborder Homoptera.
Hemipterans are hemimetabolous. Hemimetabolous insects undergo a very simple metamorphosis. As they emerge from eggs they are nymphs and to become adults they pass through different nymphal stages. Nymphs are similar in shape to the adults. They are small-sized adults.