Aphids, also known as plant lice (and in Britain as greenflies), are small plant-eating insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions.Bugs of the World, George C. McGavin, Facts on File, 1993, ISBN 0816027374 The damage they do to plants has made them enemies of farmers and gardeners the world over, but from a purely zoological standpoint they are a fascinating and very successful group of animals.

About 4,400 species of 10 families are known. Historically, many fewer families were recognized, as most species were included in the family Aphididae. Around 250 species are serious pests for agriculture and forestry as well as an annoyance for gardeners. They vary in length from one to ten millimetres.

Natural enemies include predatory lady beetles (Coleoptera: Coccinellidae), hoverfly larvae (Diptera: Syrphidae), parasitic wasps, aphid midge larvae, crab spidersPhoto of crab spider eating Aphis asclepiadis aphids on common milkweed, Anurag Agrawal, Phytophagy Laboratory, Department of Ecology and Evolutionary Biology and Department of Entomology at Cornell University. lacewings (Neuroptera: Chrysopidae), and entomopathogenic fungi like Lecanicillium lecanii and the Entomophthorales.

Aphids are distributed worldwide, but are most common in temperate zones. Also, in contrast to many taxa, species diversity is much lower in the tropics than in the temperate zones. They can migrate great distances, mainly through passive dispersal by riding on winds. For example, the currant lettuce aphid (Nasonovia ribisnigri Mosley) is believed to have spread from New Zealand to Tasmania in this way. Aphids have also been spread by human transportation of infested plant materials.

Taxonomy

Aphids are in the superfamily Aphidoidea in the homopterous division of the order Hemiptera. Recent classification within Hemiptera has reduced the old taxon "Homoptera" to two suborders: Sternorrhyncha (e.g., aphids, whiteflies, scales, psyllids, etc.) and Auchenorrhyncha (e.g., cicadas, leafhoppers, treehoppers, planthoppers, etc.) with the suborder Hemiptera containing a large group of insects known as the true bugs. More recent reclassifications have substantially rearranged the families within Aphidoidea: some old families were reduced to subfamily rank (e.g., Eriosomatidae), and many old subfamilies elevated to family rank. Taxonomically woolly conifer aphids like the pine aphid, the spruce aphid and the balsam woolly aphid are not true aphids, but adelgids, and lack the cornicles of true aphids.

Relation to phylloxera and adelgids