The order Homoptera contains many different individuals such as aphids, scale insects, cicadas, whiteflies, and leafhoppers. They demonstrate gradual metamorphosis. Adults usually have two pairs of wings. In some cases, individuals such as female scale insects never develop wings.
All members of this order have piercing-sucking mouthparts and they can be differentiated from true bugs by the fact that the beak arises from the underside of the head. This may be apparent in the illustration of the leafhopper associated with our discussion of this order.
One of the key features associated with aphids is the presence of projections that arise from the side near the posterior end of the abdomen. These structures are called cornicles. Cornicles are usually located on the top side of the fifth or sixth abdominal segment on aphids. They secrete a defensive material that warns members of the same species of the possible presence of a predator. In the line illustration of the winged aphid you can see the cornicles sticking out along the side of the tip of the abdomen.
Worldwide there are about 32,000 different species in this order with just slightly under 6,400 different species in North America north of Mexico.