Most are green or black but they can also be found in a variety of other colors as well. These cornicles secrete substances that help protect the aphids from predators. Over winter, aphids exist as eggs on perennial plants and hatch in the spring. The insects cause injury to plants by sucking the sap and juices from the soft, new growth. This damages the host plant's ability to properly process food and causes the plant to lose vigor, wilt, distort or show spots.
Aphids also can infect healthy plants with viral diseases they have picked up from unhealthy plants.
They often live in large clusters or colonies and are found together with ants. The ants feed on the honeydew produced by the aphids and protect the aphids in return, often keeping their eggs through the winter in their nests. In the spring, the ants transport the aphids to host plants and then protect them from enemies. Aphid colony on rose The honeydew is a sticky, sweet substance that is produced by the aphids when they can't use all of the sugar taken from plants. It can drip from infested trees or shrubs onto cars, sidewalks, and porches creating quite a mess.