Family Aphididae - Aphids

BugGuide is currently following the taxonomy at Aphid Species File. Tree of Life treats a number of the subfamilies as families; see that website for details.

224 genera, 40 subgenera, 1351 species of aphids currently recorded in the US and Canada, of which about 80 species are pests of food crops and ornamental plants. (1)

Aphids may be identified by two tubelike projections on the posterior, called cornicles or siphunculi. These appear to function as a means of chemical defense, emitting pheromones to alert other aphids about a predator nearby. They also offer mechanical protection, as the fluid emitted can gum up the mouthparts of the predators.

Although many different aphid species are known, they may sometimes be identified by the host plant upon which they are found. However, several different species of aphid may infest a single plant species. An attempt to organize BugGuide's aphid images by host plant is underway here.

Please note that the vast majority of BugGuide's aphid IDs have not been confirmed by specialists. The following reply from Dr. John Sorensen offers some explanation:

"Regarding your request for identification of aphids through photos. Regrettably, it is the taxonomic difficulty of aphids that makes their identification through photos very problematic. As a consequence, I long ago developed and use a policy that I have to see actual specimens, and have accurate data, including host, before commenting on aphid identification at any level beyond family. Even if those conditions have been met, the myriad of morphs and seasonal variance often preclude the assignment of a meaningful identification in this group. Nymphs cannot be reliably identified as such, or to species or often group, in almost all instances, and telling an nymph usually involves examination of the venter of the abdomen. Because alates alight on everything, even accurate species-specific host information associated with them is usually problematic unless they have been reared on the plant; this has often caused erroneous host associations in the literature. Most other experienced aphid taxonomists seem to abide by this no-photo-identification requirement, having learned through their experience, which is why few make photo identifications. In my experience, those that will do photo identifications of aphids are either very new to the group, or ultimately prove unreliable as to consistent accuracy. Unfortunately, it is the nature of the beast, both experienced aphid taxonomist and aphid."

Aphids suck juices from plants and may be quite damaging. Some are restricted to a single plant species or group of related plants. Others may alternate between two entirely unrelated host plants - for instance, Rosy Apple Aphid (Dysaphis plantaginea) begins the year on apple, then migrates to narrow-leaved plantain for several generations before winged adults return to apple trees where they produce eggs that will overwinter.

Over-wintering eggs hatch in the spring into wingless females. These wingless females are parthenogenetic (they can reproduce asexually without fertilization) and hold eggs in their bodies to give birth to living young. Their offspring are similar to the females, but some develop wings. Near autumn male and female wingless forms are born. These mate and the females lay fertilized eggs for over-wintering. Males can be winged or wingless and parthenogenetic females are usually wingless. In warm climates, living young may be produced continually with no over wintering egg stage (description adapted from University of Georgia website).

For live birth, see this image

In the course of feeding, aphids excrete a sweet liquid known as honeydew. This provides food for ants, which are known to tend aphid colonies and protect them from predators in exchange for the sweet liquid. Ants have been observed herding aphids, and stroking them to "milk" them. Some species of ants have also been known to move aphids from one plant to another when the food supply is insufficient, and some even take aphid eggs into their underground nests to help them overwinter.

Predators of aphids include (left to right, below) lacewing larvae, ladybird beetles and their larvae, harvester butterfly caterpillars, and the larvae of syrphid flies.

Aphids are also attacked by parasitic wasps, which lay eggs inside them. Parasitized aphids swell and become lighter in color and are eventually killed by the developing wasp inside. These are referred to as "aphid mummies."