Fascinating Flower Flies

White-spotted Pond Fly

While I was visiting the South March Highlands Conservation Forest last weekend I kept an eye out for other insects as well as butterflies and dragonflies. Flower flies (or hover flies) are one of my favourite types of insects. Some are tiny and hard to see, some are large and conspicuous, some are drab and some are brightly coloured. They are often striped with yellow and black, resembling bees and wasps, and many people fear them thinking that they, too, sting or bite. Flower flies rely on such mimicry to protect them from predators that would otherwise eat them, but are perfectly harmless to humans. They are often found around flowers in open areas such as parks, gardens, meadows, and sunny woodland clearings where they visit the flowers for nectar. Like hummingbirds, they often hover in place, their wings beating so fast they become invisible. They can dart forward and backward, making them fascinating to watch.

Flower flies are members of the Order Diptera, the true flies. These flies have only one pair of wings, instead of two, differentiating them from other types of flying insects such as dragonflies, butterflies, bees and beetles. They are further classified under Family Syrphidae, which can be distinguished by a spurious wing vein; that is, a vein that does not connect to other veins within the wing.

I have long been intrigued by these tiny pollinators. This fascination started when I planted my garden and started noticing all these tiny “wasps” hovering in place around my flowers! I was quite relieved to learn that they weren’t in fact wasps, and spent a lot time trying to get close enough to photograph them and figure out just what species they were. One year I planted asters in my garden, and in September 2014 the number of hover flies visiting my garden exploded! I found quite a few different types of varying sizes, and since then I’ve been hooked.

Flower flies are most visible in the spring and fall seasons, especially on sunny days with no wind. Because this has been such a strange spring, I wasn’t expecting to see very many on my visit to the South March Highlands. Indeed, it took a couple of hours hiking along the southeast portion of the conservation area before I found my first one in an open alvar where I stopped to photograph the dragonflies. Its flight style immediately caught my attention, and at first it just buzzed from flower to flower. As it showed no signs of landing, I took one photograph of it consuming nectar.

Black-shouldered Drone Fly

Then it finally decided to land on the ground where I had trouble picking it out of the lichens growing on the bedrock. Because I had so much difficulty focusing on it, I only managed the one photo before it flew off. Using my brand new field guide (“Field Guide to the Flower Flies of Northeastern North America” by Skevington et al.) as well as iNaturalist, I was able to identify this as a Black-shouldered Drone Fly (Eristalis dimidiata) which has a pair of indistinct orange bands on the third abdominal segment (aka “tergite”) that help distinguish it. I could just make this field mark out on the picture of it on the lichen.

This is species is considered to be common and is one of the first flower flies to appear in the spring. As such, it is believed to overwinter as an adult. This was my first time seeing one.

Black-shouldered Drone Fly

I didn’t expect to find a flower fly bonanza another hour later, but that is exactly what happened while returning to my car along the trail designated as “Fastout” by the OMBA. This trail skirts a large marsh close to the parking area on Old Second Line Road and is good for hearing wetland birds such as Swamp Sparrow, Common Yellowthroat and even American Bittern. I was checking the sunny openings along the wooded path for insects and saw a large, wasp-like flower fly basking on a leaf in the sunlight. I got excited, snapped a couple of photos, moved in for a better look….and then a jogger came along, and the insect flew off. I thought I had lost my chance and, discouraged, continued on my way. Around the very next bend I found a shrub in full flower sitting in a small patch of sunlight with what looked like a dozen bees circling and landing on it. I was intrigued and stopped to take a look. I saw an incredible number of flower flies feeding on the blossoms and sitting in the sunlit vegetation close by. A few bees, about 15-20 Taiga Bluets, and a couple of other interesting insects were also basking in the sunlight or buzzing about as well.

The most noticeable flower fly due to both size and abundance was the White-spotted Pond Fly (Sericomyia lata). It was large, with a distinct pattern on its abdomen, and it was the most abundant species in the clearing. Some had abdomens tipped with red, others had abdomens tipped with black. Each had the same pattern of spots on the abdomen.

White-spotted Pond Fly

This species is only one of two in its genus that has an entirely yellow face; the other species has a much different pattern on the abdomen. It is considered to be common, and is usually found visiting flowers in deciduous or pine forest.

White-spotted Pond Fly

The Oblique-banded Pond Fly (Sericomyia chrysotoxoides) is another common species related to the White-spotted Pond Fly. They have black bodies surrounded by a halo of yellow hair and thin yellow lines that slant slightly upward. I recognized this one as it appeared in my backyard two years in a row in September 2014 and 2015. It can be found in a wide range of habitats, including hilltops, pine and deciduous forests, bogs, fens, and (apparently) suburban backyards!

Oblique-banded Pond Fly

Oblique-banded Pond Fly

The third flower fly in this genus that I found was a Narrow-banded Pond Fly (Sericomyia militaris). I only saw the one, basking in the sun on a leaf, which was exactly what I saw my first one doing along the Ottawa River in September 2016 (I haven’t seen one since). It is typically found in spruce forests and bogs, but also visits other wooded areas (both pine and deciduous) where it is most often seen visiting flowers.

Narrow-banded Pond Fly

I came across only one of these flower flies with this pattern of six large spots on the abdomen, and the orangish colouration on the abdomen really made it stand out from the black and yellow flower flies. This, too, was an easy individual to identify; the Spotted Wood Fly (Somula decora). It is less common than the previous species as it prefers bogs, but it may also be found on hilltops or feeding on flowers along roadsides or in city parks.

Spotted Wood Fly

I couldn’t identify this narrow-looking individual to species, as a hand lens or microscope is needed. I believe it’s either Temnostoma balyras (common) or Temnostoma trifasciatum (rare).

Temnostoma sp.

The Common Wood Fly (Blera badia) may be common according to my new field guide, but this was the first time I have seen one (to my knowledge). I had difficulty identifying it as the wings are obscuring the orange markings along the edge of the abdomen, but iNaturalist was able to guide me in the right direction. Confusing Wood Fly (Blera confusa) is similar in appearance but has black hair above the wings (not yellow) and darker legs. Common Wood Flies are found in deciduous and mixed coniferous forests as well as bogs.

Common Wood Fly

Finally, what would a flower fly party be without this very common species, the Eastern Calligrapher (Toxomerus geminatus). These tiny flower flies are abundant in a wide range of habitats, including my suburban backyard, and as such I was able to recognize this one without needing the field guide – although it was useful in providing a common name.

Eastern Calligrapher

Other species present around the flowering shrub included several Taiga Bluets, a couple of Twice-stabbed Stink Bugs, and this golden-hued beetle. I don’t have a field guide for beetles, so I had to rely on iNaturalist to point me in the right direction. The beetles in genus Plateumaris, also known as long-horned leaf beetles, are found close to water as their larvae depend on aquatic plants such as rushes, sedges and marsh marigold.

Plateumaris sp.

Altogether there were seven species of flower fly present around that one shrub, an amazing tally for just one small sunlit clearing with a single flowering shrub. I could have spent a couple of hours there watching all the insects as they flew around, landed on the blossoms to feed, chased each other off, and mated. Most of them were new to me, so I was thrilled to have the opportunity to spend so much time getting to know them.

The next time you see a shrub or flower garden swarming with bees, stop and take a look – you might see a few of these colourful and fascinating pollinators as well!

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