Do Flies Pollinate? Their Overlooked Role in Plant Life

Flies are genuine, effective pollinators of thousands of plant species and dozens of commercially important crops. A global analysis of crop pollination found that non-bee insects, with flies as the largest component, account for roughly a quarter to half of all flower visits to crops and contribute to fruit set independently of bee activity.¹ The pollination work of flies stretches from arctic tundra to tropical cacao farms, and the sheer diversity of fly families involved makes the usual “bees do the pollinating” framing dangerously incomplete.

How Many Kinds of Flies Actually Pollinate

When people think of fly pollinators, they usually picture hoverflies, the bee-mimicking insects that hover in place near garden flowers. Hoverflies (family Syrphidae) are certainly the most studied group, but the pollination story extends far beyond them. Blowflies (Calliphoridae), flesh flies (Sarcophagidae), bee flies (Bombyliidae), dance flies (Empididae), fungus gnats (Mycetophilidae and relatives), tiny midges (Ceratopogonidae), and many others have been documented carrying pollen and triggering seed set in wild and cultivated plants. A review of fly pollination in horticultural crops found frequent reports of flower visitation and clear pollination evidence for blowflies, rhinid flies, and hoverflies across a range of crops.²

A key finding that surprised researchers is that non-hoverfly Diptera are just as specialized in their pollen-carrying behavior as hoverflies themselves. When ecologists compared pollen-transport networks, hoverflies and non-hoverfly flies showed similar levels of specialization, meaning the “other” flies were not just clumsily stumbling across flowers but were interacting with specific plant species in structured ways.³ The practical implication is that focusing conservation or agricultural efforts only on hoverflies misses a large and functionally important chunk of fly pollination.

Crops That Depend on Flies

The most famous example is chocolate. Cacao flowers are small, structurally complex, and largely inaccessible to honeybees. The primary pollinators are ceratopogonid midges in the genus Forcipomyia, tiny flies barely visible to the naked eye.⁴ Without these midges, cacao trees produce almost no fruit. This is not a niche curiosity: global chocolate production depends on a fly most people have never heard of.

Mango is another major crop where flies outperform bees. Greenhouse trials in Spain tested hoverflies (Eristalinus aeneus) as managed pollinators of mango under protected cultivation. Medium and high release densities of the hoverflies increased yields and improved fruit quality compared to both low-density releases and conventional bumblebee pollination. The economic gain for farmers ranged from about 16 to 29 percent in one season and jumped to over 200 percent in the next.⁵ Those numbers suggest that for certain crops grown in greenhouses, flies are not a backup pollinator but the best option.

Beyond cacao and mango, flies contribute to pollination in onions, carrots, peppers, strawberries, apples, oilseed rape, and many other crops. A study on oilseed rape (canola) found that many fly species were effective at delivering pollen, sharing key morphological and behavioral traits with bees that made them competent pollinators in that system.⁶

How Fly Pollination Compares to Bee Pollination

On a per-visit basis, most flies move less pollen than a honeybee or bumblebee. Their bodies tend to be smoother and less hairy, so pollen grains do not stick as readily. But flies compensate with volume. They visit flowers more frequently, in part because many fly species feed on nectar as adults but do not provision nests the way bees do, freeing them to forage continuously throughout the day. The global crop study found that although individual non-bee visits were less effective than bee visits, the sheer number of non-bee visits made up the difference, resulting in pollination services roughly comparable to those of bees overall.¹

There is an additional layer worth noting. That same study found that fruit set increased with non-bee insect visits even after accounting for bee visitation rates. In other words, flies and other non-bee visitors provide a benefit that bees alone do not deliver. This may be because flies visit different parts of the flower, visit at different times of day, or reach plants that bees ignore. Whatever the mechanism, it means that even in a field already buzzing with honeybees, losing the fly pollinators would reduce yields.

The Economic Picture

Putting a dollar figure on fly pollination is tricky because flies rarely work alone. Most animal-pollinated crops receive visits from both bees and non-bee insects. A review of 105 such crops found that 82 of them, representing a combined gross domestic product value of about $781 billion, are visited by both groups. For the small number of crops visited predominantly by non-bees, the estimated value was around $1.2 billion, compared to $19 billion for crops visited mainly by bees.⁷ Those numbers understate fly contributions, though, because the vast majority of the $781 billion joint category includes fly pollination that is hidden behind the headline bee numbers. When researchers look at fly-specific contributions within those mixed systems, the share is substantial.

Where Flies Dominate

In arctic, alpine, and subarctic environments, flies often become the primary or only pollinators. Bees are less diverse and less abundant at high latitudes and elevations because many bee species require warm, sunny conditions and nest in soil or cavities that are scarce in permafrost terrain. Flies, by contrast, thrive in cool, wet, overcast conditions. Their dominance on flowers in these environments has been documented across North America, Scandinavia, and the southern Andes, making them indispensable for plant reproduction in places where bees are rare.⁸

Urban areas are another setting where fly pollinators hold their own. A study of hoverfly assemblages in Geneva, Switzerland, recorded 81 species across urban farms and parks, with notable abundance peaking in late June.⁹ Research across urban and rural gardens in Malmö, Sweden, found that hoverflies and wild bees respond differently to urbanization, suggesting that the two groups are not interchangeable and that maintaining fly-friendly habitat matters separately from bee conservation.¹⁰ In practical terms, your backyard flower patch is already being pollinated by flies whether you realize it or not.

How Flowers Attract Fly Pollinators

Not every fly-pollinated plant smells sweet. Some of the most elaborate pollination systems in nature involve plants that smell like rotting meat or animal dung to lure flies that normally feed or lay eggs on decaying material. This strategy, sometimes called sapromyiophily, has evolved independently in many unrelated plant families and even in fungi. Chemical analysis of stinkhorn fungi and seven foul-smelling plant species found that both produce sulfur compounds typical of carrion along with compounds like indole and p-cresol that mimic feces, representing a striking case of convergent evolution.¹¹

Rafflesia cantleyi, the famous corpse flower of Southeast Asia, takes this to an extreme. Its male flowers in full bloom release dimethyl disulfide and dimethyl trisulfide, compounds associated with decomposing flesh. In lab tests, female blow flies of the species Chrysomya chani were specifically attracted to these sulfur compounds, while males were not, suggesting the plant has evolved to exploit the egg-laying instincts of female carrion flies.¹²

Other plants use pitfall traps rather than deception alone. Species in the genus Ceropegia have complex tube-shaped flowers that temporarily imprison visiting flies. In Ceropegia thaithongiae, a rare species in the montane forests of northern Thailand, only chloropid and milichiid flies were effective pollinators, entering the flower, getting trapped long enough to deposit and collect pollen, and then being released as the flower wilts.¹³

Fungus gnats, meanwhile, are fooled by plants that mimic mushrooms. Several species of Arisaema, Corybas, and Heterotropa produce mushroom-like scents, and fungus gnat eggs and larvae have been found inside their flowers, meaning the gnats are deceived into “ovipositing” on the plant rather than an actual fungus.¹⁴ The flies get nothing from the interaction. The plant gets pollinated.

Plants that genuinely reward fly visitors, on the other hand, tend to use color and scent together. Experiments with common green bottle flies showed that young flies exposed to a generic floral scent preferred yellow cues over almost every other color, and that the specific scent of oxeye daisies enhanced the attractiveness of yellow further. Moisture-rich pollen also provided nutrients that helped the flies’ ovaries mature, giving the flies a tangible payoff for visiting.¹⁵

Coevolution and Long-Tongued Flies

Some fly-plant partnerships have become so tight that the two have evolved in lockstep. In South Africa, long-proboscid flies in the genus Prosoeca (family Nemestrinidae) have developed extremely elongated mouthparts adapted to feeding from deep, tubular flowers.¹⁶ Proboscis length in Prosoeca ganglbaueri varies dramatically across different sites, ranging from about 20 to 50 millimeters. A guild of roughly 20 plant species pollinated by this fly shows floral tube depths that closely match the local fly’s proboscis length at each site. Where the flies have longer tongues, the flowers are deeper; where the flies are shorter-tongued, the flowers are shallower.¹⁷ The result is geographic mosaics of coevolution, with plant populations in one valley looking measurably different from those over the next ridge because they are tracking different local fly populations.

This kind of tight mutual shaping is familiar from classic bee-orchid or hummingbird-flower examples, but fly-driven coevolution has received a fraction of the research attention. The South African long-tongued fly system is one of the best-documented cases, and it demonstrates that flies can be just as powerful an evolutionary force as any other pollinator group.

Migratory Hoverflies and Continent-Scale Pollen Transport

One of the more remarkable recent discoveries is that migratory hoverflies ferry pollen across enormous distances. Hoverflies in the genera Episyrphus and Eupeodes migrate seasonally between continental Europe and Britain in numbers reaching hundreds of millions to over a billion individuals. Researchers who sampled pollen loads on actively migrating hoverflies found an average of about 10.5 pollen grains per fly, from up to three plant species. Scaling that up across the estimated migration volumes, spring immigrants alone could carry roughly 3 to 8 billion pollen grains into southern Britain each year, while autumn emigrants could carry 3 to 19 billion grains back toward the continent.¹⁸

More recent extrapolations push the numbers even higher, estimating that movements between the British Isles and continental Europe transfer more than 300 billion pollen grains each autumn, with the total annual transfer by migratory hoverflies likely exceeding trillions of grains.¹⁹ Wind trajectory analysis of hoverflies landing on a remote North Sea oil rig showed that the insects had originated from the Netherlands, northern Germany, and Denmark, over 500 kilometers away, confirming that they carry pollen from diverse source populations across international borders.²⁰

This long-distance pollen movement has implications for plant genetics. It connects plant populations that would otherwise be reproductively isolated, potentially maintaining genetic diversity across fragmented landscapes. For conservation biologists worried about small, isolated wildflower populations losing genetic variability, migratory hoverflies may be an underappreciated lifeline.

Flies That Pollinate and Kill Pests at the Same Time

A practical advantage of some hoverflies is that they pull double duty. Adult hoverflies visit flowers and pollinate crops, while their larvae are voracious predators of aphids. Greenhouse trials with Eupeodes corollae showed that releasing laboratory-reared hoverflies enhanced yields of multiple horticultural crops while simultaneously delivering effective, chemical-free control of resident aphid pests.²¹ On melon and strawberry, hoverfly releases suppressed cotton aphid populations by 50 to 99 percent, depending on timing and release rate. On tomato, weekly releases led to fruit set as high as 95 percent. On melon, a slightly lower release density achieved 100 percent fruit set.

This “two for one” characteristic makes hoverflies an attractive option for integrated pest management in greenhouses, where growers already pay for biological control agents and managed pollinators separately. A single hoverfly release could replace both, cutting costs and reducing reliance on chemical pesticides. Commercial hoverfly rearing is still in its early stages compared to the well-established bumblebee industry, but the economic incentives are there.

Fly Pollination Goes Back to the Dinosaurs

Flies are not latecomers to the pollination game. Fossil evidence shows that long-proboscid flies were visiting and likely pollinating plants during the Cretaceous Period, alongside the dinosaurs. Researchers described a well-preserved fly in the extinct family Zhangsolvidae with Exesipollenites-like pollen grains still clinging to its body. That pollen type is associated with the Bennettitales, cycad-like gymnosperms that lived roughly 250 to 70 million years ago.²² This means flies were pollinating seed plants before many modern flowering plant lineages even existed. The relationship between flies and plants is not a recent ecological convenience; it is an ancient partnership that predates much of the floral diversity we see today.

Why Flies Get Ignored and Why That Matters

The overwhelming focus on bees in pollination research and public awareness campaigns has created a blind spot. Bee decline is a genuine concern, but the framing of pollination as a “bee issue” means that fly conservation receives little attention. Hoverflies and other fly pollinators face many of the same pressures bees do: habitat loss, pesticide exposure, and climate change. Neonicotinoid residues, for example, have been measured in pollen, nectar, soil, wild plant tissue, and puddles on farmland at levels that pose risks to flower-visiting insects broadly, not just bees. These residues turn up in the nectar and pollen of field-margin wildflowers, meaning flies foraging away from treated crops still encounter contamination.

Fly pollinators also respond differently to land-use changes than bees do. Because many fly species breed in decaying organic matter, dung, wet soil, or dead wood rather than in the cavities and bare ground bees prefer, the habitat features that support fly populations are not the same as those targeted by bee-friendly planting campaigns. A wildflower strip designed to help bees may do little for hoverflies if the surrounding landscape lacks the larval breeding sites they need. The global crop study made this point explicitly: non-bee insects respond differently than bees to landscape structure, which likely makes their crop pollination services more robust to certain types of land-use change, but also vulnerable to different threats.¹

If you are planting a garden with pollinators in mind, the simplest adjustment is to stop thinking exclusively about bees. Flies are attracted to open, bowl-shaped flowers and umbels (the flat-topped clusters of tiny flowers found on plants like dill, fennel, and Queen Anne’s lace). They tend to prefer white, yellow, and pale-colored blooms. Leaving patches of bare, damp soil, compost, and fallen leaves provides larval habitat for hoverflies and other beneficial flies. Avoiding blanket insecticide applications helps too, but the habitat piece is at least as important: you can plant all the flowers you want, but if there is nowhere for fly larvae to develop, the adults will not be around to pollinate them.