Say flies, and one instantly thinks about dirt and disease. But in truth they are among the cleanest of insects.

They are a grossly misunderstood order of insects. They are excellent pollinators, aid in criminal investigation, composting, pest control and increasing soil fertility, and of course in scientific research. They are the true flies.

Why are true flies named so?

Several insects such as the butterflies, dragonflies, mayflies, or fireflies bear the word ‘flies’ in their names, but they are not flies. To distinguish what we know as the fly from such insects, they are described as true flies. These are insects that have only one pair of wings. In true flies (referred to in this article as fly/flies) the hind wings are reduced to a pair of club-shaped structures called halteres and so fly using only one pair of wings. To stay airborne and move forward, the fly must beat its wings as much as two hundred times a second.

That is also why it is difficult to swat flies. The halteres function as gyroscopes, providing fine balances during flight. Flies can therefore perform complex movements in flight to deftly avoid any obstacles or swats.

Along with their close relatives, the midges and mosquitoes, flies belong to the order Diptera (Di, meaning two; ptera, meaning wings). Of the 27 orders of insects, Diptera ranks second for abundance.

The housefly being the frequently seen one, there is a general impression that all flies are dark and drab like them. Many flies are brilliantly coloured, some exhibiting iridescence, and others with a variety of body forms and appearances. The Catalogue of Life, an online platform lists 160,591 species of flies, distributed among 160 families (as of March 2021).

This species richness is also responsible for the variety of services humans obtain from them. Fruit fly, a favourite among researchers, also holds the unique distinction of being the first living creature to travel to space, as early as 1947. NASA operates a Fruit Fly Lab aboard the International Space Station to study the effects of spaceflight on living organisms.

Flies, the pollinators

While the services rendered by fruit flies in scientific research is well documented, their role in pollination is less known. Most discussions on pollination by insects centre around bees. Flies in general are excellent and better pollinators than bees for many reasons. They fly long distances to feed on nectar, whereas bees are bound by the needs of their colonies or nests. Bees cannot fly long distances as they have to feed their larvae, provision their nests with pollen, or in the case of solitary bees bring back pollen for the larva in their nest. This attachment to their nests restricts their movement and they rarely fly beyond a kilometre, whereas flies have no such limitations. Hoverflies have been recorded flying 50-110-kilometre distances.

A literature review and analysis, published in 2019 in the Annual Review of Entomology noted that flies from families Syrphidae, Calliphoridae, Muscidae, Sarcophagidae, Tachinidae, and Bombyliidae were among the top 10 non-bee visitors of crops. The study showed that flies were the most important pollinators after bees. Over 70% of the 105 crops they reviewed were pollinated by flies. Of these they found that syrphid and calliphorid flies were the most common ones that visited a wide range of crops. The flies from both these families serve other purposes too. For those who grow crops under glasshouses, flies are a welcome pollinator, as bees may sting due to their aversion to glasshouses.

Flies of the family Syrphidae are known as hover flies. There are at least 368 species in 77 genera found in India according to a book published by the Zoological Society of India (ZSI). Of these two new species of hover fly in the genus Eristalinus were recently discovered in the Gangetic plains by a team from ZSI this year; Entomologist Sankararaman from Amruta College of Agricultural Sciences has described five new species. Similarly Kerala has reported 60 species of hover flies rediscovering Eristalinus (Merodonoides) multifarious after 45 years.

Syrphids or hover flies are bee-mimics, an advantage for their success as pollinators. Not only do they look like bees, but many also behave like them, hovering over flowers or some even making buzzing sounds, which is an adaptation to hoodwink likely predators while flying among flowers in the open, collecting pollen and nectar. Nectar for energy and pollen is their source of nutrients especially for sexual maturity.

Many species of syrphids are known to produce several generations in a year, thereby enhancing pollination opportunities. From coriander, onion, carrot, pepper, and capsicum to apples, pears, cherry or strawberry to name a few, hover flies may be found on them.

The larvae of hover flies are voracious eaters. They are predaceous, and particularly fond of feeding on aphids and small soft bodied, sap-sucking insects; those larvae that live in aquatic habitats feed on a range of organic materials. So, while the adults are pollinators, their larvae are pest control agents and recyclers of organic materials.

Some species of hover flies are long distance migrators too.

Calliphorid flies or blow flies come a close second in their service as pollinators of a wide variety of crops. As per a paper published in 2022, 32 genera and 134 species are recorded from India. They are famous as pollinators of the mango trees; but they also pollinate several other fruiting trees such as litchi, guava and apple to name a few. They forage on flowers for nectar that is their source of energy and pollen, the protein rich food needed for their growth and reproduction. They fly long distances to find the perfect place to lay eggs. And during this flight they visit flowers and transfer pollen.

Blow flies generally have a bad reputation as insects that spread diseases. This is because they are attracted to dead and decomposing organic materials, animal carcasses and corpses on which they mate and lay eggs. But this very process results in two kinds of benefits. As their larvae feed on the animal waste it is broken down for further decomposition by microbes. Also known as the blue bottle fly/green bottle fly, their reproductive process is welcomed by forensic entomologists involved in criminal investigation. Their larval stages provide important clues for investigation.

The decreasing diversity of bees and the continuous and drastic fall in their numbers is a cause for major concern. Flies are as good if not better than bees as pollinators. Their bodies are hairy and so can trap a lot of pollen. The foraging patterns, however, differ. The bees are selective, following a set pattern which limits the number of flowers they visit and how they forage among them in a field. Flies are not, visiting many more flowers than bees. Bees will not come out if there is a drop in the temperature whereas flies are known to start foraging earlier than bees. Flies’ fecundity is another positive sign; bees produce lesser generations per year in comparison with, for e.g. hover flies. Having realised the importance of flies in food production, farmers are now rearing some hover fly species commercially.

Other flies and their ecosystem services

Among the not so widely studied are the soldier flies. The larva of the black soldier fly Hermetia illucens is efficient at decomposing wastes and has garnered attention for its ability to rapidly break down organic waste materials ranging from kitchen & food wastes to animal faeces. A study published last year described how the gut microorganisms present in the larvae of Hermetia illucens were able to break down the polyurethane that was served to them as food. They found that black soldier fly larvae not only survived solely on polyurethane and water but also gained weight, the consumption influenced gut microbial community.

The long-legged fly, an exquisitely dainty and colourful fly, belongs to the family Dolichopodidae. This is one of the 20 families of Diptera that exhibit predatory behaviour and therefore render a valuable service as pest control agents. They are however poorly studied in India.

Dolichopodid flies can be easily recognised by the way they stand on their long legs, as if standing on six stilts, their slender bodies that sport a metallic shine – blue, green or golden-green, bulging eyes and small wings. There are some species that feed on mosquito larvae. These are fidgety flies that move in short spurts of flights as they hunt for their prey. Their larvae can be found on wet or moist soils feeding on decaying organic matter. They feed on aphids, thrips, spider mite, springtails, whiteflies, leafhoppers and midges which are pests of agriculture. They deserve to be called “friends of farmers”.

Banner image: A hoverfly spotted in Ladakh. Image by Geetha Iyer.

Citation:

• Phylum Athropoda. In: Zhang, Z.-Q. (Ed.) Animal Biodiversity: An Outline of Higher-level Classification and Survey of Taxonomic Richness (Addenda 2013). Zootaxa 3703 (1): 017–026 (30 Aug. 2013)   https://www.mapress.com/zootaxa/list/2013/3703(1).html
• Roy, Bristi & Sengupta, Jayita & Naskar, Atanu & Banerjee, Dhriti. (2024): A Catalogue of Indian Hoverflies (Insecta: Diptera: Syrphidae).
• Geetha Iyer. Minature Giants: Insect Stories Beyond the Ordinary. Penguin Random House, India. 2025. 218 pages. (page 132-135)
• Xifeng Wang et al (2026): Biodegradation of polyurethane by black soldier fly larvae and the function of gut microorganisms . Environmental Entomology, Volume 55, Issue 1, February 2026.  https://doi.org/10.1093/ee/nvaf131
• Kavya Gireesh Pillai1, Bijoy ChenthamaraKshan and GiGi Poulose (2026): MAJOR PREDATORY DIPTERA (PANORPIDA: ANTLIOPHORA) OF INDIA. Indian Journal of Entomology 88(4):937-950 (2026) https://doi.org/10.55446/IJE.2025.3391

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Priyanka Shankar Editor

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BiodiversityConservationEcologyEcosystem servicesInsectsIndia

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