The Homoptera have the dubious distinction of being probably the most destructive insects of all. They include aphids, leafhoppers, cicadas, and scale insects: approximately 45,000 species worldwide, 6,000 in North America. Some taxonomists place the Homoptera with true bugs, but the current thinking is, the differences are great enough to place them in their own order.
Homopteran wings are uniformly membranous, unlike the true bugs which have a leathery portion at the base of their wings. All Homopterans feed exclusively on plants, but their diets vary tremendously, as do their reproductive methods. Many species reproduce sexually, while others do so parthenogenically (without mating). Cicadas and leafhoppers mate sexually, and most females have large ovipositors which they use to deposit eggs into slits they cut in plant tissue. But Aphids can reproduce without having sex, and are among the most destructive of all homopterans - theoretically, one female aphid is capable of producing billions of offspring. All homopterans undergo simple metamorphosis.
Many insects in this order exude waxy secretions which protect them from attack and make them impervious to water; others secrete a sweet secretion called honeydew. Members of the order hymenoptera, the ants, have learned to "farm" aphids for their secretions -- in turn, they protect the aphid colonies from attack by other predators and parasites. This symbiotic relationship is one of the most fascinating in nature.