Aphid

Aphids are small, sap-sucking insects belonging to the family Aphididae.

They are highly successful organisms because they can multiply at incredible speeds. While some people call them greenflies or blackflies, individuals within a single species can vary widely in color. Some species, like woolly aphids, even appear fluffy and white.

Because they can colonize many different types of plants, they are very important to ecosystems. However, they are also considered serious pests in agriculture, forestry, and gardening. Around 400 species of aphids specifically target food and fiber crops.

To feed, aphids use specialized mouthparts called stylets.

These thin structures are enclosed in a protective sheath called a rostrum. An aphid finds a plant by using visual cues and then using its antennae to smell the surface. Once it lands, it probes the plant to find the right tissue. The aphid aims for the phloem, which is the part of the plant that carries sugary sap. Because the sap is under high pressure, it is forced directly into the aphid's food canal.

Sometimes aphids also drink xylem sap, which is much more dilute. They may use xylem sap to help maintain their water balance.

The way aphids reproduce is quite unique and allows for rapid population growth.

Many species use asexual reproduction, meaning they do not need males to create offspring. Flightless females give live birth to female nymphs. In a process called telescoping generations, these newborn nymphs may already be pregnant themselves. This allows the population to multiply very quickly.

If the environment becomes crowded or the food source becomes poor, winged females called alates develop. These winged adults can fly to new plants to start new colonies.

Aphids have several ways to defend themselves from predators.

On their fifth abdominal segment, many aphids have a pair of tubes called cornicles. These cornicles exude a quick-hardening defensive fluid known as cornicle wax.

They also produce a sweet, sticky liquid called honeydew. While honeydew can cause problems like the growth of sooty molds on plants, it also creates interesting relationships in nature. Some species of ants, known as dairying ants, protect aphids from predators. In exchange, the ants eat the honeydew. This is a mutualistic relationship where both species benefit.

Natural enemies play a major role in controlling aphid numbers.

Predatory insects like ladybugs and hoverfly larvae hunt aphids frequently. Other hunters include parasitic wasps, crab spiders, and lacewing larvae. Even certain fungi can act as a natural control by infecting the aphids. Because aphids often hide on the undersides of leaves, they can be difficult to reach. This makes large-scale control hard, as they can develop resistance to many insecticides. On a smaller scale, gardeners can use soap sprays or water jets to manage them.

We can learn much about aphid history through the fossil record.

Aphids likely evolved from a common ancestor during the Early Permian period. Because their bodies are soft, they do not fossilize easily in soil. However, they are often preserved in plant resin that hardens into amber.

The oldest known fossil is a species named Triassoaphis cubitus from the Triassic period. As flowering plants, or angiosperms, began to diversify, aphids also began to specialize. This led to a massive increase in the number of different aphid species over time.

Aphids are found all over the world, though they are most common in temperate zones.

They are excellent travelers and can migrate long distances using the wind. Winged aphids can rise as high as 600 meters into the air to be carried by strong gusts. For example, the currant-lettuce aphid was believed to have moved from New Zealand to Tasmania around 2004 via easterly winds. Humans also help spread them by transporting infested plants from one place to another. This movement has helped some species become nearly cosmopolitan, meaning they are found almost everywhere.