Aphid Identifier: What Do Aphids Look Like, and What Gets Rid of Them

What do aphids look like?

Start with size, because it rules out most of the alternatives in one step. An adult aphid is 1 to 4 mm, roughly a poppy seed. Then look at the body. It is pear-shaped and soft, with no hard wing case and no shell.

After that, look at the back end. Aphids carry two small tubes called cornicles, one on each side, pointing backwards like a pair of tiny exhaust pipes. Nothing else you will find on a plant has them. So if you can see cornicles, you are finished, and if you cannot, keep working down the list.

One more thing worth knowing before you look. Most aphids in a colony are wingless, but crowded colonies also produce winged individuals that leave to start new ones. Those look noticeably different, slimmer and darker, and people often report them as a separate insect on the same plant.

How to identify an aphid from a photo

The identifier at the top of this page reads a photo and names what it sees. It works best when the photo gives it something to work with, so three things help.

• Get close, then steady. Body shape is the first thing the model reads, and a blurry cluster of green dots could be almost anything.
• Include the rear end if you can. The cornicles are the deciding feature, and a photo that shows them is far more useful than one taken from directly above.
• Shoot the cluster, not one insect. The packed-together habit is itself evidence, and it gives a sense of scale against the stem.

If the photo comes back as something else, that is worth taking seriously rather than retrying. Plenty of plant problems get called aphids, and the look-alikes section below covers the ones that come up most.

Aphid colours, and what each one usually is

Colour follows species and host plant, not age, so it is a genuinely useful clue. The one exception is worth remembering: an aphid that has just moulted looks pale for a while, whatever species it is.

Greenfly and blackfly are just aphids

British gardeners say greenfly and blackfly, and both terms simply mean aphids by colour. Neither is a fly. Blackfly on broad beans is almost always the black bean aphid, and greenfly on roses is usually the rose aphid.

The naming does cause one real mix-up. A genuine blackfly, in the family Simuliidae, is a small biting fly that goes for people and livestock near running water. If something bit you, it was not an aphid. Our bug bite identification guide sorts out what did.

Woolly aphids, the white fluffy ones on bark

If what you found looks less like an insect and more like scraps of cotton wool stuck to a branch, you have woolly aphids, also spelled wooly aphids. They belong to the subfamily Eriosomatinae, and they coat themselves in white waxy threads produced by glands along the body.

That wax does two jobs. It hides the insect, and it sheds water and sprays, which is exactly why a contact spray that clears ordinary aphids often does nothing here. People also mistake the fluff for a fungus or mould and treat for the wrong problem entirely.

Most woolly aphid colonies on a mature tree do no lasting harm, and the usual advice is to leave them for the predators. The exception is the woolly apple aphid, because its feeding causes galls that split the bark and open the way for canker. So on a young or valuable apple tree it is worth acting, and worth asking a local extension service what is recommended in your area.

Root aphids, the ones you never see

Root aphids feed underground on roots rather than on foliage. That is what makes them so frustrating. The plant yellows, wilts in the afternoon, and stops growing, while the leaves look perfectly clean and you find nothing however hard you search the top.

The test is to tip the plant out of its pot and look at the root ball. You are looking for pale insects among the roots and a white waxy dust on the soil and pot walls. People very often call these mealybugs, which is an easy mistake, because both produce wax underground.

What do aphid eggs look like?

Small, oval, and shiny black. You will find them on bark, in bud joints, and tucked along stems, usually in autumn. They sit out the winter there and hatch in spring.

Here is the part that surprises people. For most of the growing season there are no eggs at all, because summer aphids skip that stage and give birth to live young instead. Eggs only appear when the colony switches to sexual reproduction as days shorten. Consequently winter is the one time you can act on an aphid population before it exists, by scrubbing or oiling the bark where eggs overwinter.

Bugs that get mistaken for aphids

Plenty of small things on plants get called aphids. These are the ones that come up most, and the feature that separates each.

Two of these have their own guides here. For the webbing-and-stippling problem see spider mites, and for the wider group of small white things on plants see tiny white bugs.

What aphids actually do to a plant

Aphids feed by pushing fine stylets into the plant and tapping the phloem, the vessels carrying sugars around the plant. A handful of aphids costs a healthy plant nothing. A heavy colony causes four separate problems.

• Distorted growth. New shoots curl, pucker, and yellow, because the aphids are taking sap from tissue that is still expanding.
• Honeydew. Aphids excrete sugary waste, which lands on whatever is below. That is the sticky film on leaves, patio furniture, and car roofs parked under a lime tree.
• Sooty mould. A black fungus grows on the honeydew. It does not attack the plant, but it blocks light from the leaf and looks awful.
• Plant viruses. The serious one. Aphids move between plants while feeding and carry viruses with them, which matters far more in a vegetable plot than the sap loss does.

Why aphid numbers explode in a week

This is the question behind most aphid searches. A plant looks clean on Monday and is covered by Saturday, and the reason is a genuinely strange piece of biology.

Through spring and summer, aphids reproduce without males. Females give birth to live daughters, and those daughters are already carrying their own developing daughters at birth. Three generations are effectively stacked inside one insect. No eggs, no mating, no waiting.

When the colony gets crowded or the plant starts failing, some young develop wings and fly off to start again elsewhere. Then as autumn shortens the days, the colony finally produces males, mates, and lays the overwintering eggs. So the population you are looking at in July is the descendant of a handful of eggs that hatched in March.

The practical lesson follows directly. Treating once is never enough, because a few survivors rebuild in about a week. Treating early, when you find the first cluster, is worth more than treating hard later.

Why ants protect aphids

Ants farm aphids. The honeydew aphids excrete is a sugar source, and ants harvest it directly from the colony, sometimes stroking the aphids with their antennae to encourage it.

In return the ants defend their herd. They drive off ladybirds, attack lacewing larvae, and in some cases carry aphids to fresh growth. Some species even move root aphids between pots. So an ant trail running up a stem tells you two useful things at once: there are aphids above, and the predators that would normally deal with them are being kept away.

Consequently the ants are often the better target. A band of horticultural glue around the stem, or dealing with the nest itself, lets the natural predators back in and the aphid problem frequently solves itself.

What eats aphids

Quite a lot, which is why most aphid outbreaks end without intervention. Learning to recognise the predators matters, because several of them look alarming and get squashed by mistake.

A note on what not to reach for. Broad-spectrum insecticide kills ladybirds, lacewings, hoverfly larvae, and parasitic wasps along with the aphids. Since aphids rebuild faster than any of their predators do, the usual result is a worse outbreak two weeks later on a plant with nothing left to defend it.

Aphids on roses and other specific plants

Most aphids are fussy about their host, which is useful, because the plant narrows the species list before you have looked at a single insect.

Two plant-specific tricks are worth knowing. Pinching out the growing tip of broad beans removes the black bean aphid colony with it, and it is standard practice once the lower pods have set. For houseplants, the single most effective habit is quarantining new arrivals for a fortnight, since most indoor aphid problems walk in on a plant from a shop.

Do aphids bite humans?

No. An aphid’s mouthparts are fine stylets built to pierce plant tissue and reach the phloem, and they are not built for skin. Aphids carry no disease that affects people and do nothing to a person beyond making leaves sticky.

There is one small caveat that explains the reports. A winged aphid that lands on you will sometimes probe briefly before flying on, which can sting for a second. It takes nothing and it leaves no mark. So if you have actual itchy bites, something else caused them, and our bug bite identification guide is the place to start.

Pest control disclaimer. Photo-based identification can help, but it is not always perfect. For dangerous spiders, large infestations, or anything you are unsure about, contact a licensed pest control professional.