Because of their complex life cycle, a single species of aphid can have different body forms, some four-winged, but mostly wingless. Overall, they are soft-bodied, plump, pear-shaped, and tiny. All aphids have two tubelike projections on the hind end of the body, called cornicles or siphunculi, which apparently emit scents that warn other aphids of danger or can emit a defensive goo to deter predators. Aphids are commonly green, yellow, or brown, but the color is quite variable among the many, many species. Most aphids are slow-moving and sedentary.
Length: to about ¼ inch (varies with species).
Habitat and Conservation
Aphids are usually found on their host plants. Some species require certain types of plants and can be indentified, in large part, by naming the plant they are on. Other species aren’t so particular. Many aphids are serious agricultural and garden pests, as their feeding deprives the plant of nutrients and the punctures they make injure the plant’s veins. Aphids sometimes transmit diseases to plants, the way mosquitoes and ticks can transmit diseases to people.
Aphids, like all members of the “true bug” family, have strawlike mouthparts specialized for piercing and sucking. They jab the pointed tubes of their mouths into a leaf, flower, or stem, then suck the sap from the plant. Because this is essentially what lice do to animals, aphids are sometimes called “plant lice.” Because plant juices are high in sugar, excess sugars are excreted by aphids, sometimes abundantly. This fluid, called honeydew, is collected as food by ants and other insects.
Aphids have a complex life cycle. After overwintering as eggs, the aphids that hatch in spring are all females and reproduce asexually (without mating). Their offspring, which are born live (not hatching from eggs), are genetically identical to their mothers. At some point, the females give birth to aphids that develop wings, which can disperse from the original colony. Late in the season, male and female forms are born. These mate, and eggs are laid to overwinter for the next season.
Aphids can cause serious damage to crops and garden plants, wilting them and sometimes transmitting diseases. The honeydew they excrete can cause sooty mold on plants and can leave spots on cars and other objects. Fortunately, many insects prey on aphids and keep them in check without help from us.
Lacewings, lady beetles, and hordes of other insects prey on sweet, juicy aphids. Other insects, especially certain ants, collect the honeydew, an important food source for them. Some ants stroke aphids, “milking” them for honeydew, and repay their aphid “herds” by defending them from harm.