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Leafhoppers are a species of insects in the family Cicadellidae, order Homoptera, a group that also includes the cicadas, whiteflies, aphids, and scale insects. There are about 20,000 species of leafhoppers, including about 2,500 species in North America.

Leafhoppers are leaf-feeding herbivores that use their sucking mouthparts to pierce the plant tissues and feed on their juices, in some cases causing economically important damage to crop species. Leafhoppers have relatively specific feeding habits, and they occur only on particular species of plants, or closely related groups. Some species of leafhoppers secrete honeydew from the anus; this a sugar-rich solution is similar to that produced by the closely related aphids.

Leafhoppers are rather small insects, the largest being no more than 0.5 inch (13 mm) in body length, but most species only being a few millimeters long. Leafhoppers have short, bristle like antennae, and a double row of spines running along the tibia of their hind legs. Leafhoppers have wings, which are held tent-like back over the thorax and abdomen when the insect is not flying. Most species are beautifully marked with stark color patterns that can be seen upon close viewing, especially on their somewhat thickened fore-wings, and sometimes their head and thorax. The tropical species Cardioscarta pulchella is brilliantly colored with red, black, and white hues, and is commonly used as a model in Central American folk art.

Leafhoppers have three stages in their life cycle: egg, nymph, and adult. Most species only produce one or two generations per year, overwintering as either adults or eggs.

Some leafhoppers use weak, species-specific sounds to communicate with each other. These leafhoppers produce their noises using structures known as tymbals, which are anatomically similar to the much-louder sound-producing organs of cicadas.

A few species are migratory in North America. The beet leafhopper (Circulifer tenellus), for example, maintains permanent populations in the southern parts of its range, but migrates northward as the weather and availability of food become favorable during the growing season. When climatic conditions deteriorate again at the end of summer, beet leafhoppers may migrate south, although these individuals are not of the same generation as the animals that made the earlier, northward migration.

Some leafhoppers cause important damage to crop plants. The potato leafhopper (Empoasca fabae)

causes damage to potato and bean leaves by plugging the vascular tissues, causing the death of foliage. Other species of leafhoppers cause injuries to leaves at their feeding sites, or they damage foliage by removing excessive quantities of sugars and chloroplasts. Some species of leafhoppers are the vectors of infectious diseases of crop plants. The beet leafhopper, for example, is responsible for spreading curly top, a disease of sugar beets, spinach, beans, squash, and some other vegetables.