Aphids are soft-bodied, slow-moving insects, often with a fat abdomen; they cluster on the new growth of many plants, sucking fluids from tender shoots and causing wilting or distortion. They come in various colors, including green, pink, red, and black; some are winged. Some kinds appear only at particular times of year;others seem to have a preference for a specific plant or plants. The honeydew they excrete attracts ants and can encourage sooty mold. Where there's a severe infestation of both aphids and ants, you must control both insects.
Aphid infestations often seem to develop overnight, but they rarely last longer than a few weeks. Knock the pests off plants with sharp blasts of water; you'll also get help from many natural predators, including lacewings, damsel bugs, ladybugs, syrphid flies, predatory midges, parasitic wasps, lizards, and small birds. Hot weather will kill aphids.
If you want help from beneficials, avoid chemical controls. Later in the season, when aphids have naturally died out and beneficials have departed, wash off honeydew residue or sooty mold with soap spray or plain water.