Flower Flies as Pollinators

Syrphid flies or flower flies (Toxomerus)

Syrphid flies or flower flies (Toxomerus) on St. John’s wort. © Beatriz Moisset


Among all the tiny flower visitors, butterflies stand out for their beauty and bees for their role as pollinators. But many other visitors deserve our attention. The flies of the Syrphidae family are among them.


Syrphus fly on seaside goldenrod. © Beatriz Moisset


Eristalis transversa on sunflower © Beatriz Moisset


In England, they are known as hover flies, and in the United States they are often called flower flies. Those two common names describe them beautifully. They are seen at flowers frequently and they hover above them, suspended in air like diminutive helicopters.



Helophilus on New England aster. © Beatriz Moisset

Their looks deceive countless people. I usually get one of two responses when I point them out to somebody unfamiliar with these little fellows. Those who despise house flies say “These cannot be flies. They look like bees”. The ones who fear stings ask “Would that bee sting me?”

Even more amusing is when somebody illustrates an article or a book about bees with an image of these excellent impersonators.

The likeness to bees is not accidental. Syrphid flies have been perfecting this disguise for millions of years, not to deceive us but birds and other predators. Evidently, they succeed only too well if they can also trick human observers.

Syrphid flies can be as abundant as bees at flowers or even more so. In November, when the cold weather has chased most pollinators away and when a few hardy flowers manage to persist, syrphid flies are still hanging around in gardens. Although not as proficient as bees at pollinating flowers, they do a fair amount of transporting pollen from blossom to blossom. In fact, some small flowers, flat, open, easy to reach, can be pollinated entirely by these little flies if there are no bees around.

Canola field. © Beatriz Moisset

Canola field. © Beatriz Moisset

Syrphid flies may pollinate some crops almost as efficiently as bees do. The individual flies may not be very efficient, but if they are abundant enough they make up in numbers what they lack in skill. One example is that of canola or rapeseed crops.

Recently, I learned a delicious little tidbit. Just as syrphid flies use visual deception to elude predators, some orchids resort to a different kind of deception to exploit syrphid flies. Their flowers emit aromas similar to the smell of aphids, a powerful attractant to some of these flies. The disenchanted orchid visitor probably leaves the flower after failing to find any aphids; but the orchid has already glued a sac of pollen to its body. The forgetful fly is likely to repeat its mistake at a different flower, depositing the pollen as was the orchid’s intention.

Aphids, two eggs of syrphid fly and a larva (upper right corner, partly hidden by an aphid). © Beatriz Moisset

Aphids, two eggs of syrphid fly and a larva (upper right corner, partly hidden by an aphid). © Beatriz Moisset

Flies start life as eggs that become larvae, totally different from winged adults. Most times these larvae or maggots go unnoticed by the gardener; but some of them are worth mentioning because they play a role perhaps even more important than that of pollinators.

The larvae of many syrphid flies feed on aphids. It takes a sharp eye to find them in the garden. But if you look around at aphid colonies, you are likely to find some. When freshly emerged from eggs they are about the same size as the aphids or even smaller, but they grow considerably larger. They are blind and thrash around in search of prey. They would be helpless and die of starvation if their provident mothers didn’t lay eggs in close proximity to healthy, fast growing aphid colonies.


Aphids and syrphid larva on milkweed. © Beatriz Moisset


Aphids and syrphid larva on arrowwood. © Beatriz Moisset

It is rather fascinating to see one of these larvae clutch at an aphid with its mouth parts and proceed to suck it dry. Oddly, other aphids seem oblivious to the threat of this voracious eater. I have seen aphids walking all over a syrphid larva which is busily devouring one of its sisters.

Such little dramas go on all the time in the wildlife garden. It is good to know how nature keeps the balance between plants, plant eaters and predators. Pesticides are not needed as long as these cycles go on.

More on syrphid flies, Bugguide.net

© 2013, Beatriz Moisset. All rights reserved. This article is the property of Native Plants and Wildlife Gardens. We have received many requests to reprint our work. Our policy is that you are free to use a short excerpt which must give proper credit to the author, and must include a link back to the original post on our site. Please use the contact form above if you have any questions.

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  1. James C. Trager says

    Hola Beatriz – Another venue where our digital pathways cross!

    You mentioned the obliviousness of aphids toward their syrphid larva predators. Also interesting is that ants are well known for defending aphids from most parasites and predators, to protect the source of their sugary waste product, honeydew, an important energy source for ant colonies. However, ants also seem to be oblivious to the syrphid larvae, walking right over them as thought they weren’t there, in their quest to gather up the sweet honeydew droplets.

  2. says

    Wonderful post, Beatriz! It’s amazing how much wildlife we actually have in our gardens when we take the time to stop and look really closely. The Syrphid flies have developed an amazing defense strategy by so closely resembling bees. But they serve such an important function for gardeners by keeping the aphid populations under control. This is such important information to share. Thank you :)
    Carole Sevilla Brown recently posted..Speaking at Todays Horticulture Symposium at Longwood Gardens

  3. Mark Donahue says

    Very informative post! I see these little fellows(fellas?) in my garden all the time. I knew they were some type of fly, but hadn’t explored their true identity.

  4. says

    I was taking photos of these after I read something about them and I think it was from you, but this summer I will really have to look more closely..wonderful information…Michelle


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