Flower flies: surprise pollinators

This summer, I took a lot of photos of pollinators on flowers. I am now sorting through them trying to identify the different insects. To my surprise, some of the pollinators were actually flies. And they’re actually quite beautiful, some mimicking bees and wasps with similar striping and hair.

Is it a fly?

Once you know what to look for, flies are easy to spot. They have a few easily recognizable features that distinguish them from other pollinators — their heads are larger, and are almost all eyes, and they have very short antennae. Flies also have only two wings, while bees and wasps have four wings — athough I can’t get a close enough look or photo to count wings. This video Is it a bee or a fly?, from Bees in our Backyard, provides a quirky, visual overview of how to tell flies from bees.

An insect with a PR problem

When I hear the word ‘flies’, I immediately think of house flies. Growing up, my mother waged a continual battle to keep them out of her kitchen. In the summer, we always had a spiral sticky trap (called Flypaper) hanging from the ceiling, and a fly-swatter mounted on the wall like a sword. It was our duty to shoo or kill any fly that dared approach our food. I don’t see many house flies or fly-swatters anymore; I guess their disappearance is yet another sign of declining insect populations.

The flies that I’ve seen in my garden are much more posh than house flies. Most belong to the syrphid family, commonly known as hover flies, or flower flies. They visit flowers for nectar, and sometimes pollen too. They’re valuable pollinators; it’s estimated that they carry out one-third of agricultural pollination services (Field Guide to the Flower Flies of Northeastern North America, p. 12, at Ottawa Public Library). Flies complement the pollination work done by other insects because they prefer cooler temperatures, between 15°C and 25°C. Unlike other pollinators, flies aren’t very active in afternoons or in warmer times because they risk desiccating (Field Guide, p. 21).

Flower flies are also very handy to have around because they’re ‘beneficial insects’. They help control insects pests, along with more familiar predators like ladybugs and lacewings. Flower fly larvae eat soft-bodied insects, such as like aphids, mites, mealybugs, thrips, and caterpillars.

Identifying flower flies in the garden

I tried to identify the flower flies in my photos using a new book, the Field Guide to the Flower Flies of Northeastern North America, by Jeffery Skevington et al (at OPL). Dr. Skevington lives here in Ottawa, and I have attended a few of his interesting and entertaining public presentations, so I was keen to try out his book.

Well, it turns out that identifying flies isn’t so easy for an amateur like me. There are many kinds, and similar ones with subtle differences that require magnification to see. There is no way I can tell if their legs are hairy or smooth, or examine their unique facial features. My photos certainly aren’t close-up enough for that.

In the book, the easier-to-identify flies are handily marked with an ‘eye’ symbol. Undeterred, I set out to find matches for my flower flies, and I hoped to find lots of ‘eye’ symbols for encouragement. To double-check my preliminary IDs, I also submitted the photos to iNaturalist to see what others thought.

Flying specks

Calligrapher flies are tiny, dainty flies, with ornamental abdominal markings. Eastern Calligraphers were common visitors in my garden in the spring. I even managed to identify this pretty fly on my own back in June of 2019.

Eastern Calligrapher on a ‘Prairie Fire’ Crabapple blossom (June 6, 2019).

After examining my photos more carefully, it turns out that some of the Eastern Calligraphers were actually Margined Calligraphers. According to the Field Guide, they are active from mid-March to early October, and are one of the most common and abundant syrphids in our area. (p. 380).

A Margined Calligrapher on a Wild Strawberry flower (May 26, 2019).

The next tiny fly isn’t so easy to identify because its kin look so similar. It is some kind of Epistrophe (according to iNaturalist), or maybe an Epistophella. (Field Guide, p 434)

A little fly in the Genus Epistrophe (probably) visiting ‘Fireworks’ Goldenrod (October 10, 2019).

I had a lot of trouble identifying this very tiny, metallic fly. It isn’t a syrphid fly, it’s a Long-legged Fly. We’ve also seen ones that are metallic gold, instead of green. You can learn about them in this online article, the Long legged Fly. Like flower flies, adults visit flowers for nectar, and larvae eat soft-bodied insects. Their larvae camouflage themselves by incorporating surrounding debris while making their cocoons.

A Long-legged Fly sitting on a Red Osier Dogwood leaf (September 13, 2019).

An overly-dressed fly

Very early in spring, I saw some big flies on our Pussy Willows. I believe this one is a Drone fly of some sort, such as a Black-shouldered Drone Fly. (Field Guide, p. 113) I think this shiny, pinstriped insect looks quite well-dressed, which belies its diet recycling sewage.

Some kind of Drone fly (Genus Eristalis) on Pussy Willow (April 25, 2019).

Wasp mimics

Other flies in my photos look remarkably like wasps. Some flower flies obtain protection by looking like stinging wasps and bees, even though they are harmless. When I took pictures of this Four-lined Hornet fly, I thought it was a wasp.

A Four-lined Hornet fly sunning itself on an Anise Hyssop leaf. (August 13, 2019)

I think this next fly is an Eastern Hornet Fly, based on its markings, and its taste for goldenrod flowers (Field Guide, p. 134). To me its eyes look like a decorative, striped turban. It is an uncommon fly though, found in hardwood forests, so maybe it’s unlikely to be visiting my urban yard.

Possibly an Eastern Hornet Fly on Silverod, a creamy-yellow type of goldenrod (August 25, 2019).

To see a couple of bumblebee mimics that have been in my garden, see my previous posts: Resident Spring Bees and visiting butterflies to see a Greater Bee-fly, and The Case of the Missing Bumblebees which features a Robber Fly.

Attracting flower flies to the garden

Like so many other insects in our yard, flower flies need lots of native plants. In North America, you won’t find many flower flies in areas filled with non-native plants, like disturbed meadows of European weeds, and urban gardens packed with introduced ornamental flowers (Field Guide, p. 22). Since I have been adding native plants to my garden, I am now attracting lots of flower flies.

In the book Attracting beneficial bugs to your garden: a natural approach to pest control (at OPL), Jessica Walliser recommends growing plants with many tiny flowers that allow easy access to nectar. She then profiles suitable plants, both native and non-native. You should also provide habitat so beneficial insects will live in your garden throughout the growing season. They’ll be there to address pest issues whenever they occur.

Now that I’ve learned a bit about flower flies, I am especially happy to see them in my yard. They’ll help the bees pollinate my flowers, and keep my new vegetable garden free of destructive pests. They’re also pretty — and pretty cool.

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