Aphids are tiny (under ¼-inch), and often invisible to the naked eye. Various species can appear white, black, brown, gray, yellow, light green, or even pink! Some may have a waxy or woolly coating. They have pear-shaped bodies with long antennae; the nymphs look similar to adults. Most species have two short tubes (called cornicles) projecting from their hind end.
Adults are usually wingless, but most species can develop a winged form when populations become crowded, so that when food quality suffers, the insects can travel to other plants, reproduce, and start a new colony. Aphids usually feed in large groups, although you might occasionally see them singly or in small numbers.
While aphids in general feed on a wide variety of plants, different species of aphids can be specific to certain plants. For example, some species include bean aphids, cabbage aphids, potato aphids, green peach aphids, melon aphids, and woolly apple aphids.
Photo credit: GrowVeg.com. Some aphids are darker colors like brown. The potato aphid is a common brown aphid.
Nymphs and adults feed on plant juices, attacking leaves, stems, buds, flowers, fruit, and/or roots, depending on species. Most especially like succulent or new growth. Some, such as the green peach aphid, feed on a variety of plants, while others, such as the rosy apple aphid, focus on one or just a few plant hosts.
- Look for misshapen, curling, stunted, or yellow leaves. Be sure to check the undersides of leaves, aphids love to hide there.
- If the leaves or stems are covered with a sticky substance, that is a sign that aphids may have been sipping sap. The honeydew, a sugary liquid produced by the insects as waste, can attract other insects, such as ants, which gather the substance for food. When aphids feed on trees, their honeydew can drop onto cars, outdoor furniture, driveways, etc.
- The honeydew can sometimes develop a fungal growth called sooty mold, causing branches and leaves to appear black.
- Aphids feeding on flowers or fruit can cause them to become distorted.
- Some aphid species cause galls to form on roots or leaves.
- Aphids may transmit viruses to certain plants, and also attract other insects that prey on them.
Photo Credit: John Obermeyer/Purdue University. Aphids can be various colors, including yellow, and produce a sticky honeydew substance.