Aphids are tiny, sap-feeding insects in the order Hemiptera, the true bugs. Most adult aphids are between 1⁄16 and 1⁄8-inch long, but remember that everything begins life small. Pick your favorite color, and there is probably a similarly colored aphid! Depending on the species, they may be black, gray, white, red, orange, yellow, green, blue-green, blue, purple, brown, and tan. Most aphids (family Aphididae) are smooth and teardrop-shaped, but some are covered with white wax filaments, giving them a fluffy or fuzzy appearance. Take a good look with a hand lens, and you'll see the distinctive "cornicles" on their rear end. Cornicles emit a defensive chemical that is harmless to us. I think they look like dual exhaust pipes on a car. Some aphids are generalists feeding on many kinds of plants; some are specialists feeding on only one species or perhaps a group of related plants. All sap-feeders excrete "honeydew." The sugary honeydew evaporates, making a sticky, shiny mess on the leaves, your car, or whatever is under the plant. Later, black sooty mold grows on the honeydew, interfering with the plant's photosynthesis and increasing its messy appearance.
Why are aphids everywhere this growing season? There is no clear answer. Sometimes insects appear in cycles. The mild weather with two cold snaps during the winter of 2022–2023 impacted plants, pests, and predatory insects. In the case of aphids, it may be a combination of the spring drought and our gardening routines. We often apply fertilizers in the spring to give our plants a boost of nutrients. Aphids are attracted to young, tender, fast-growing plant parts rich in nitrogen. Aphids are also attracted to stressed plants. Our plants were drought-stressed this spring! It is a bad combination.
Figure 2: Left, Aphids on a rose stem. Photo: Katelyn Erb Styer, Nescopeck Agway. Right, Aphids on butterfly milkweed. Photo: Mandy L. Smith, Penn State
Let's factor in the very high reproductive rate of aphids. Aphids have a life cycle of simple metamorphosis: egg, several stages of nymphs, then the mature adult that may be wingless or winged. Some females reproduce parthenogenetically without mating. These aphids often bear live female young instead of laying eggs. The lifespan of an adult may be only a month, but it reaches maturity in as few as four to ten days. Aphids reproduce faster than any other insect!
Figure 3: Aphids that have 'mummified' as a result of being parasitized. Photo: Tom Butzler, Penn State
A gardener may notice distorted leaves or stems before seeing the tiny insects. Some ants tend the aphids to feed on their honeydew. Be on the lookout for natural predators. Ladybugs (ladybird beetles, family Coccinellidae) and especially their orange and black larvae are voracious predators of aphids. Flower fly larvae (family Syrphidae) and lacewing larvae (family Chrysopidae) feed on aphids, too. There are itty-bitty parasitoid wasps (family Braconidae) that insert an egg into a living aphid, turning it into a round, chubby "mummy" that acts as a nursery for its next generation. Birds, especially warblers and hummingbirds, are consumers of aphids.
How can a gardener manage these aphids? I was taught to squish them gently with my fingers. If that is not an option for you, blast them with a stream of water from the garden hose! Be sure to spray up, then spray down to include the undersides of the leaves. Plain water will knock them off, and few will return. Do look for natural insect predators before treating the aphids. If you need to control the aphids, a simple treatment with insecticidal soap is also effective. Remember that a solution made with dish detergent will damage plant tissue, so do not use homemade recipes. Avoid systemic insecticides which travel throughout the plant, including the flowers. These products impact good insects like aphid predators and pollinators.
For information on specific aphids, follow these links to articles from Penn State Extension:
