syrphid flies | Garden Ecology Lab

A syrphid flying over a clarkia, photo by Devon Johnson

We have been seeing syrphid flies (family: Syrphidae) in great abundance this summer over at the Garden Ecology lab’s research garden, so much so, that our field research team has begun to call it the year of the syrphids! These bee-mimicking, skittish pollinators have particularly loved the native and cultivar yarrow we have planted in our plots. Although their abundance has recently dipped–likely because Yarrow (Achillea millefolium) is done with its first round of bloom–we still see them buzzing around.

Syrphid flies, also known as flower flies or hover flies are a common visitor of gardens. You may see them buzzing around bright flowers or fighting mid air. They are important pollinators and feed off of nectar and pollen in their adult stage. Additionally, in their larval form, they are great at reducing aphid populations, but are extremely susceptible to pesticides.

Line drawing of *Toxomerus* spp. life cycle, credit to Brett Blaauw, Department of Entomology, Michigan State University

The life cycle¹ of syrphids start with the adults laying eggs in leaves of infested plants. After about three days, they hatch into their voracious, blind, larval stage.

The larvae feast on small pests like aphids, leafhoppers, scales, and thrips. The larvae do this by moving along plants, lifting their heads to try and seize and pierce their prey with their triple-pointed dart inside their mouth². After slurping their prey dry, they will discard the exoskeleton.

Larvae will develop through a few instars and after 1 to 3 weeks will go into a pupal stage on the host plant or on the soil. After two weeks, an adult emerges.

Syrphid larvae with an aphid in its grasp. Photo by Oregon State University

Hover fly pupa. Attribution © Adam Grimwade, all rights reserved⁵

In the pacific northwest, our common syrphid is Scaeva pyrastri. It is unique in that rather than overwintering as a larvae, S. Pyrastri overwinters as an adult. Three to seven generations occur in a year, with possibility for the higher counts depending on the region and species. Another species, originally native to Europe, the drone fly (Eristalis tenax³) is named after male honey bees because it is mimics them so well. Other mimics in Syrphidae lay their eggs in the nests of bumblebees or social wasps, where the larvae eat dead bees and detritus.

Their quick movements and bee-like appearance can make syrphid flies hard to identify.

To identify a flying insect as a syrphid, look for a single pair of wings. Flies (Order: diptera) do not have a second pair of wings like bees. Instead they have a vestige of hind wings called halteres that look like little nubs beneath their wings. These act like gyroscopes to help the fly balance during unique in-flight maneuvers. Also look for large, forward facing compound eyes typical of any dipterans. In our lab, we’ve see a wide range of size and different colors. Syrphids can be anywhere from a tenth of an inch to half an inch long, and have black or brown bodies with white or yellow spots and stripes. Fun fact: most hover fly mouths are extendable ‘sponges’ that mop up nectar and pollen.

Common oblique syrphid (*Allograpta obliqu*a). Notice the nub-like halteres below the wings. Photo by Ron Hemberger

Flower flies are extremely important to pest control and pollination, 40% of syrphid species larvae feast on the previously mentioned prey, and each larvae can eat up to 400 aphids during development!

Unfortunately, the larvae of syrphids are similar to many other species so are hard to identify. However, they are usually on pest infested plants and may be seen near adult syrphids. Look for their typical ‘stretching’ behavior while they are on the hunt. If you have a pest problem, avoid using pesticides or insecticides! These kill the syrphids that can help with pests. Instead, promoting syrphids or other pest eaters like ladybugs and lacewings by providing a variety of insectary plants can help you in the long run.

A large syrphid on our native yarrow, with a threat nearby! Photo by Devon Johnson

As previously mentioned, yarrow (Achillea millefolium) has been our most successful syrphid-attracting plant in our lab this year. Syrphid flower preference varies based on the subfamily, according to studies. The subfamily Eristalinae is attracted to white flowers, Pipizinae prefer white and yellow, and Syrphinae is more general. Link to an article going more in depth on syrphid flower preference here⁴.

Not coincidentally, native yarrow is primarily white, while our cultivars are yellow and pink. Observationally, syrphids visit yellow yarrow at a similar rate as they do the native, while our pink cultivar saw next to no syrphid visitors. We recommend planting yarrow as well as a variety of native flowering plants to support these pollinators. Leave leaf litter and debris around flowering plants, too. These provide protected overwintering sites which syrphids rely on⁷.

Syrphid on our yarrow ‘Moonshine’ cultivar. Photo by Devon Johnson

Currently, no syrphid species are on the U.S. Endangered Species Act lists, but like many insects, this underappreciated pollinator is understudied and biodiversity of this group is not well tracked. In Britain, however, some hoverflies have been placed on their Biodiversity Action Plan.⁶

Whether syrphids are endangered or not, we can help biodiversity by promoting native pollinators and planting native plants in our yards and gardens.

Credits

I have been so grateful for the opportunity to assist Jen Hayes with her nativar research project. For the past year and a half, I have learned so much in the world of plant and pollinator relationships. One of the most valuable things I have learned, which I use every day in my own garden, is how to quickly identify bees. In the field, we observe each flower plot for five minutes and record the different things that visit. Being able to identify a fly from a bee, or a bee from a wasp is very important in order to obtain accurate data. I wanted to share the process we use to quickly identify bees in the field and hopefully answer some questions you may have had about what was buzzing in your garden.

A small black Halictidae bee examining the Douglas aster cultivar, Sauvie Snow. The photo was taken by Tyler Spofford at Oak Creek Center for Urban Horticulture in Corvallis, OR.

Once the sun has risen and the chill of the morning has left, bees begin their foraging routine. Male bumblebees, out foraging too late, emerge from the layers of Zinnia flowers. Hundreds of bees possibly pass through your garden in a single day, from flower to flower, collecting pollen and nectar. But what are they? Are they native? Are they helpful in the garden? These are all questions I have whenever I see something buzzing on the mint, exploring the flower patch, or pollinating the tomatoes.

The first things I always look for are the antennae and the number of wings. The flies that are most often confused with bees have short, almost non-existent antennae, whereas bees will have noticeable, segmented antennae. The wings are also something to look: flies only have one pair of wings and bees have two, the forewings and hindwings. Be sure to look closely! There are flies known as hoverflies or syrphid flies that have incredible mimicry adaptations. Look at these two insects on this butterfly bush. Although almost identical, you can see the top insect does not have noticeable antennae. That’s because it is a honey bee mimic!

The bottom insect is a honey bee and the top insect is a syrphid fly that is a mimic of honey bees. The photo was taken by Tyler Sato Spofford at Lewis Brown Horticulture Farm in Corvallis, OR.

If you have established that it is a bee and not a fly, there are other things to look for to identify the bee to a more specific taxonomic level. The coloration of the bee could help if it is green or red, but there are many bees that have different variations of black and white. What I like to look for next is the pollen baskets, also known as the corbiculae. Megachilidae bees carry the pollen on the underside of their abdomen, like bright yellow furry bellies. Another distinguishing factor for Megachilidae bees is how they fly. The abdomen of the bee will usually curl upwards while in flight. Mellisodes bees carry the pollen on their hind legs but the baskets are dramatically bigger than honeybees or bumbles. We like to think of them as pollen pants! Mellisodes bees are also known as long-horn bees because of their disproportionately long antennae.

A mellisodes collecting pollen. Look at those pollen pants!

If the bee does not have any special coloration or noticeably different corbiculae, it could be one of many other genera we have in Oregon. Halictidae bees range in size from the tip of a pen to the size of a penny. They are usually black or black and white and are VERY difficult to distinguish in the field. There are details we have to look for in the lab such as the number of “panels” in the wings or if they have one versus two sub-antennal sutures.

The other bees we see while doing research include wasps, honeybees, and bumblebees. There are so many variations of Bombus here in Oregon it is almost like a scavenger hunt. Because of all the color and striping variations, we use the PNW Bumblebee Atlas to help us identify species in the field.

Garden Ecology Lab

Socio-ecological research in urban and suburban garden systems

Tag Archives: syrphid flies

The Underappreciated Syrphid Fly

Credits

What’s buzzing in my garden?: A quick guide to garden bee ID.