Tiny and varied in color, these insects suck the juice of plants to the point where the plants, wilt, dehydrate, and possibly die. They also spread viruses that can kill plants. They are a popular nemesis to gardeners and farmers when they form large colonies on vegetation. Some species of lady beetles, moth larvae, and wasps eat them, however, some aphids are toxic giving them an advantage against predators. Most female aphids are wingless, but winged ones will return to their original plant after starting populations elsewhere. They can be mechanically removes (killed by hand), but small size and quick escape make it a inefficient means of removing them.
Aphids come in a variety of species. Colors vary by species, but popular ones are green, yellow, or white. A group called "woolly aphids" are covered in a white, waxy substance that resembles cotton or fuzz. All types of aphids pierce the plant at its leaves and stems. They digest plant juices and excrete a sticky, sugary 'honeydew' liquid which may attract other garden insects. Ants have been seen shepherding aphids and harvesting their sweet honeydew for consumption for themselves and their ant colonies. The honeydew can also turn black with mold and look like a layer of dark ash, or soot, on the leaves and stems, ruining the beauty of an ornamental plant.
Note: The above text is EXCLUSIVE to the site www.InsectIdentification.org. It is the product of hours of research and work made possible with the help of contributors, educators, and topic specialists. If you happen upon this text anywhere else on the internet or in print, please let us know at InsectIdentification AT gmail DOT com so that we may take appropriate action against the offender / offending site and continue to protect this original work.
* MAP NOTES: The territorial heat map above showcases (in red) the states and territories of North America where the Aphids may be found (but is not limited to). This sort of data is useful when attempting to see concentrations of particular species across the continent as well as revealing possible migratory patterns over a species' given lifespan. Some insects are naturally confined by environment, weather, mating habits, food resources and the like while others see widespread expansion across most, or all, of North America. States/Territories shown above are a general indicator of areas inhabited by the Aphids. Insects generally go where they please, typically driven by diet, environmental changes, and / or mating habits.
Colors: green; black; yellow 
