Aphids are tiny, soft-bodied insects belonging to the superfamily Aphidoidea, with over 5,000 known species distributed across almost every terrestrial habitat on Earth. They range in size from about 1 to 6 mm and come in a remarkable variety of colours — green, yellow, black, pink, grey, and white — often matching or contrasting with their host plants. Most species are equipped with a pair of tube-like structures called cornicles on their abdomen, which secrete defensive compounds when the aphid is threatened. Though individually small and seemingly fragile, aphids are among the most ecologically and economically significant insects in existence.
One of the most remarkable features of aphids is their reproductive strategy. For much of the year, females reproduce parthenogenetically — giving birth to live female nymphs without any need for mating — allowing populations to grow at extraordinary speed. A single aphid can theoretically give rise to billions of descendants within a season. In autumn, many species produce sexual forms that mate and lay overwintering eggs, often on a completely different host plant from the one used in summer. This alternation between host plants, combined with the switch between asexual and sexual reproduction, is one of the most complex life cycle strategies found in the insect world.
Aphids feed by inserting needle-like mouthparts called stylets into plant tissue and drawing out phloem sap. Because phloem sap is rich in sugars but low in essential amino acids, aphids must consume vast quantities of it, excreting the excess sugar as honeydew. This sticky substance coats leaves and surfaces below infested plants and often supports the growth of sooty mould, while also attracting ants, which actively farm aphid colonies for the honeydew and protect them from predators. Beyond direct feeding damage, many aphid species are vectors of plant viruses, transmitting pathogens far more efficiently than the physical harm of their feeding alone.
Aphids occupy a central role in food webs and ecosystems. They are a vital food source for a wide range of predators including ladybirds, lacewings, hoverfly larvae, parasitic wasps, and many birds. Their honeydew supports diverse communities of insects and fungi. At the same time, they have developed sophisticated defences — waxy coatings, alarm pheromones released from cornicles, sequestered plant toxins, and mutualistic relationships with ants. Managing aphids in agriculture remains one of the great ongoing challenges in crop protection, driving research into biological control, resistant varieties, and the complex ecology that keeps their populations in balance in natural settings.
Types of Aphids on Plants
Black bean aphid (Aphis fabae)
One of the most recognisable and destructive agricultural aphids, the black bean aphid is a small, matt-black insect that forms dense colonies on broad beans, sugar beet, and many other crops. It overwinters as eggs on spindle trees (Euonymus) before migrating to summer hosts in spring. Large infestations can cause severe leaf curl and stunting.
Green peach aphid (Myzus persicae)
A pale yellowish-green aphid with a remarkably wide host range — it attacks hundreds of plant species from potatoes to peaches. It is considered one of the world’s most economically damaging aphids largely because it is an efficient vector of plant viruses, transmitting over 100 different viral diseases to crops worldwide.
Woolly apple aphid (Eriosoma lanigerum)
Named for the characteristic white, waxy wool it secretes to protect its colonies, this aphid attacks apple trees and related species. It feeds on bark and roots, producing galls that weaken the tree. The woolly coating makes it highly visible on branches and makes chemical control more difficult.
Rose aphid (Macrosiphum rosae)
A large, pinkish-green aphid with long dark cornicles that is almost synonymous with rose gardening troubles. Colonies cluster on new buds and shoot tips, causing distorted growth. It alternates between roses in summer and teasel or scabious plants in other seasons.
Cabbage aphid (Brevicoryne brassicae)
A greyish-green, mealy-looking aphid that feeds exclusively on brassicas — cabbages, kale, mustard, and related plants. It is covered in a waxy grey powder that gives colonies a distinctive dusty appearance. This species stores compounds from its host plants that it converts into a mustard-oil defence when attacked by predators.
Pea aphid (Acyrthosiphon pisum)
A relatively large, bright green aphid that is one of the most studied insects in biology. It feeds on legumes including peas, alfalfa, and clover and has become a laboratory model organism for studying aphid genetics, symbiosis with bacteria, and host-plant interactions. Some populations produce red forms through carotenoid pigments — unusually, these are synthesised by the aphid itself rather than obtained from food.
Sycamore aphid (Drepanosiphum platanoidis)
A large, pale green aphid found almost exclusively on sycamore trees. Unlike many aphids, it rarely forms dense colonies, preferring a more scattered distribution. It produces abundant honeydew, which drops onto surfaces below and supports growth of sooty mould, making it noticeable to anyone parking beneath a sycamore in summer.
Aphid of Douglas fir (Adelges cooleyi)
Strictly speaking a close relative of true aphids, this adelgid alternates between Douglas fir and Sitka spruce. On spruce it causes distinctive pineapple-shaped galls at branch tips. It is one of several gall-forming adelgids that cause significant damage in forestry and Christmas tree plantations.
Lettuce root aphid (Pemphigus bursarius)
An unusual species that spends part of its life cycle inside galls on poplar leaf stalks, then migrates underground to feed on lettuce roots. Because it attacks the root system, infestations can be well advanced before any above-ground symptoms appear, making it a particularly insidious pest of commercial lettuce production.
Grain aphid (Sitobion avenae)
One of the most economically significant cereal pests in temperate regions, the grain aphid is a green to reddish-brown insect that feeds directly on wheat and barley ears during grain fill, reducing yield. It also transmits barley yellow dwarf virus, compounding the damage it causes to cereal crops.
Bird cherry-oat aphid (Rhopalosiphum padi)
This species overwinters on bird cherry trees, where it causes curling and reddening of leaves in spring, before migrating to cereal crops in summer. It is a major vector of barley yellow dwarf virus and one of the most abundant aphids found in grain crops across the northern hemisphere.
Potato aphid (Macrosiphum euphorbiae)
A large, elongated aphid that is pale green or pinkish in colour and attacks a very wide range of plants including potatoes, tomatoes, and roses. Like the green peach aphid, it is important as a virus vector, transmitting potato virus Y and other serious pathogens. It can reproduce rapidly under warm conditions.
Vine aphid / grape phylloxera (Daktulosphaira vitifoliae)
Technically a phylloxerid rather than a true aphid, this tiny insect caused the devastation of European vineyards in the late 19th century after being accidentally introduced from North America. It feeds on vine roots, creating galls that allow fungal infection and ultimately kill the plant. The solution — grafting European vines onto resistant American rootstock — remains standard practice to this day.
Rosy apple aphid (Dysaphis plantaginea)
A purplish-pink to grey aphid that is one of the most damaging pests of apple orchards. Even small infestations cause severe fruit deformation — apples become small, twisted, and unmarketable. It overwinters on apple trees and moves to plantain (Plantago) as a secondary host in summer.
Conifer woolly aphid (Pineus pini)
This adelgid forms distinctive white woolly patches on the bark of pine trees, feeding on the phloem beneath. Heavy infestations weaken branches and can cause dieback in young trees. Like other adelgids it produces copious wax filaments that protect the colony and make it immediately recognisable.
Shallot aphid (Myzus ascalonicus)
A small, pale aphid that is unusual in being entirely asexual — no sexual forms have ever been found. It attacks onions, shallots, strawberries, and a range of other plants. Despite reproducing only parthenogenetically, it has spread widely around the world and is considered a significant pest in stored bulbs as well as growing crops.
Melon and cotton aphid (Aphis gossypii)
An extremely polyphagous species found on hundreds of host plants worldwide, including cucumbers, melons, cotton, and citrus. It is particularly problematic in greenhouses where warm, stable conditions allow populations to explode. It has developed resistance to many insecticide classes and transmits numerous important plant viruses.
Oleander aphid (Aphis nerii)
A strikingly yellow aphid with black cornicles and legs, forming bright colonies on oleander, milkweed, and related plants. It sequesters toxic cardenolide compounds from its host plants, making it unpalatable to most predators. Its bold yellow colouration is thought to serve as a warning to would-be attackers.
Lime aphid (Eucallipterus tiliae)
A pale yellow aphid found on lime trees (Tilia species) that produces prodigious quantities of sticky honeydew, a perennial nuisance for anything parked or sitting beneath urban limes in summer. Large infestations cause leaf distortion and support growth of sooty mould fungi on the honeydew deposits below.
Spotted alfalfa aphid (Therioaphis maculata)
A yellowish aphid with distinctive rows of dark spots across its back, feeding on alfalfa and related legumes. It was accidentally introduced to the United States in the 1950s and caused devastating losses to alfalfa crops before biological control agents and resistant varieties reduced its impact.
Spruce aphid (Elatobium abietinum)
Unlike most aphids, the spruce aphid is most active during mild winter and early spring periods, feeding on old needles of spruce trees. Damage — browning and needle drop — often appears in late winter and early spring, leading gardeners to wrongly attribute it to frost. Large outbreaks can defoliate ornamental spruces severely.
Hawthorn-parsley aphid (Dysaphis apiifolia)
This species completes a complex host alternation between hawthorn, where it causes tightly curled, pink-tinged leaves in spring, and members of the carrot family — parsley, parsnip, and related plants — where it feeds through summer. Heavy infestations on hawthorn create distinctive bunched, distorted leaf clusters at branch tips.
Giant willow aphid (Tuberolachnus salignus)
The largest aphid in Europe and one of the largest in the world, reaching up to 5–6 mm in length. It forms dense, conspicuous brown colonies on the bark of willow stems and branches. Despite its size and abundance, it has no known sexual phase and reproduces entirely through parthenogenesis, yet populations are found across the globe.
Banana aphid (Pentalonia nigronervosa)
A small, dark reddish-brown aphid that is one of the most serious pests of banana plantations worldwide. It feeds at the base of the pseudostem and in the leaf axils of banana plants and is the primary vector of banana bunchy top virus, a devastating disease that stunts and kills infected plants. Management of this aphid is central to controlling the spread of the disease.