• Joe Dlugo

Fall is for the Flies

Many Benign and Benificial Flies are About in the Late Season Garden

A fly of the genus Tachina, dark with spiked hairs and brown eyes, on a pink flower with a yellow center
Tachina sp.

I am going to start this by being honest: I dislike fall. Always have, and as I ascend in years it is looking hopelessly like I always will. I search desperately every year to find enjoyment in it. The garden is dying back and the trees are going to sleep. The daylight withers. The colorful summer birds of the woods have flown away. Misery.

Back in the fine warm and fruitful days of summer I was complaining of the pending fall when a good friend told me there's something to love about October, because it is the best month for flies around here. Flies.

Now there are many methods that work when attempting to persuade. Mentioning the merits of flies is typically not one of them. Ask anyone what they want to come back as in the next life and no one will say "a fly." The thought of gooey maggot babies, disease infestations, their little grubby paws rubbing together plotting your demise. I am not ignorant that they must have a purpose, but if there were ever a way I was going to enjoy fall it would certainly not be due to the flies.

An ornate yellow and black fly, a mimic of yellowjackets, sips nectar from an orange milkweed flower
Spilomyia sp.

Then October came along, a desperate time. So after having managed years of ignorance, I actually did something that few humans have done before me: I took someone's advice. The open-minded gardener in me took over. I decided to attempt to enjoy flies during "the best month for flies."

So I have spent the past month actively looking for flies, doing my best to identify them, and where I thought I would have to force myself to carry on, the world of flies only got more and more interesting. These creatures wear many important hats and have a lot to contribute to the success of a garden. I can safely say we'd be remiss to not appreciate them.

A tiny flower fly of the genus Toxomerus, orange and black striped with maroon eyes, alights atop a white flower with a purple center.
Toxomerus sp.

So What in the world is a fly? 


This is a question many people think they know the answer to. Some form of negative jest aimed at one species (the house fly) is culturally appropriate as a reply, and I myself have engaged in this. But as with most general knowledge of the very, very complex natural world, it is well, general. I had some reading to do. So I cracked the field guide to the fly section, family Diptera. It means "two wings" in Greek. Go ahead and look at the photos and count them – it's always two. Why is this so special? Because bees, wasps, butterflies, dragonflies and whole bunch of other bugs have four wings. So now it's easy to tell what's a fly and what's not, right?

Not so fast. Perhaps the most photographed bee in the world is actually a fly. A blog post from brilliant bee blogger Rusty Burlew (honeybeesuite.com) goes to detail this well. Even people with good eyes for seeing nature have a hard time telling the difference sometimes.

A colorful yellow, black and orange fly, Helophilus fasciatus, seen here on  purple Aster flower
Helophilus fasciatus

Other differences can be apparent with flies. Instead of long, thin antennae like bees and wasps have, flies have two little nubby antennae. And instead of thin, egg-shaped eyes set far apart on the face, flies typically have large domed eyes that are often close and in some species even joined in the center of the face. If you endeavor to notice flies, you'll also notice many other differences, some physical, some behavioral. For instance, when a bee or wasp flies away from a flower you'll notice it rather clumsily dismount and zig zag away, whereas a fly will simply pop up and disappear in a flash.

A small gray and black house fly with maroon eyes stands atop the pink flowers of a Buddleia butterfly bush
Muscidae sp. - House Fly

There is seemingly endless diversity in flies.


The first thing that struck me was just how many kinds of flies can be found about a garden. When I first started looking it was as if I never see the same type twice. I quickly learned why. In North America alone we have about 19,600 described species. That's five times the amount of bee species–a notoriously difficult group to identify. Heck, one in ten species described on EARTH is a fly (a total of about 110,000 species named to date)! Many, many more remain undescribed. It quickly occurred to me that if I were willing to fill a lifetime, or six or seventeen times that many, I could do worse things with my waking hours than to spend efforts aimed at further understanding the role of flies.

So with all these flies in North America (approximately 1,000 species of hover flies, 4,000 tachinid flies, 600 house flies, etc...) how in the world can this be kept straight? After many years of birdwatching I have that innate desire to know exactly what I'm looking at. For the casual gardener/fly observer, that is pretty much impossible. Their diminutive size, microscopic characteristics and sheer numbers pose need for expensive observation equipment and lengthy time spent acquiring the necessary skills. But as a seasoned vet in noticing bees I realized it may only take a couple seasons to recognize the giss (birder term for general impression, size and shape) of a certain flies. In due time it became quite easy to distinguish the common types by family. Hover flies (Syrphidae) are generally easy- as they can be identified by their striped abdomens and hovering behavior near flowers. Tachinid flies (Tachinidae) have spiny abdomens and are usually chunky, house flies (Muscidae) look like, well, flies.

An intimidating looking fly with spiked hair, red abdomen, maroon eyes, and red antennae on a yellow Bidens flower.
Peleteria sp.

Benefit to Gardeners


This wouldn't be going on a gardening blog if there weren't some nifty thing flies do for our precious plots, many of which I am beginning to realize were happening without my notice. Certainly pollination is important, but for all its popularity, our gardens don't run on pollination alone. Perhaps the most beloved of flies (if that is a word that can be applied to them) are the hover flies, AKA flower flies, denizens of the genus Syrphidae, are as adults important pollintors. As larvae, they are aphid-hungry monsters. Every seasoned gardener knows the horrors of aphids. Many are aware that ladybugs help with this problem, but hoverflies are nature's ultimate go-to in this regard. Their maggots thrash about the branches of garden plants looking to collide with an unlucky aphid. They consume many. By all means, put out flowers and be good to your hoverflies.

Another helper is the tachinid fly. As I mentioned before there are a great many types of these flies about on our continent (~1400). They aim at depositing or injecting their eggs on or near caterpillars. The story is a familiar one, the eggs get into the caterpillar and consume it, leaving vital organs for the last. Many a gardener knows the destruction of an unchecked caterpillar population. To test this, I just recently extracted a kale plant from my garden and brought it indoors. The plant had a few very small caterpillars of cabbage white (Pieris rapae) on it. Void of natural enemies, the caterpillars consumed the plant bare in just a few days and got big and fat. The Kale plants left outside in the patch appeared untouched. Now you say some caterpillars are delightful to have around and there is little stopping tachinid flies from occasionally targeting the likes of monarchs and swallowtails, but without them to keep a natural check on populations, it is safe to say that much of the good green earth would be quickly gobbled to the ground.

Flies have several other beneficial roles, such as being decomposers (like compost?), and as players in the grand game of predator and prey their presence is often vital for those beautiful bug-eating birds we love so dearly.

A thin fly with outstretched wings and orange spots on abdomen on a white flower
Cylindromyia interrupta

Welcoming Fall Flies


Words most people thought they'd never hear. But it's a new day and surprises are fun. I am a beginner at this type of gardening, so the many flies I've photographed for this post have simply piggy-backed off my planting for the bees. Late season garden flowers such as tickseed (Bidens sp.), bog sage (Salvia uliginosa), or any aster species will have our two-winged friends show up in good numbers. Native Pacific Northwest plants to consider for flies include seaside daisy (Erigeron glaucus), globe gilia (Gilia capitata), and California poppy (Eschscholzia californica). The spectacular native Douglas aster (Aster subspicatus) may be the ultimate choice for attracting flies, as it is long-blooming, free-spreading and produces an abundance of seeds for the birds to enjoy.

The world of attracting flies extends beyond flowers, of course, and it's likely a frequently-encountered pollinator fly may have a life history that requires any one of a broad range of possibilities. Most people aren't too thrilled by the thought of bringing in road-killed raccoon corpses to attract young bottlefly larvae, but hesitance to cut the stems of aphid-infested plants in your garden will likely yield an opportunity to watch hoverfly larvae do their best work, and they will do it well without the need to further damage your plant.



A very large dark blue fly at rest on a white background.
Cuterebra sp. - Bot Fly

Learning More


Springboarding off the immense popularity of bees, there is a growing movement underway to encourage learning about the wide range of ways insects help gardeners and ecosystems. Although resources are less numerous than their apid cousins, I've included a few books, online materials, and even a couple podcasts that helped me get a start. After spending so much time learning how to see these insects I can safely I say will never ignore them again. I look forward to a day when all their hard work gives them a well-deserved reputation of respect, and perhaps even admiration.



A small flower fly with thick hind legs on a yellow Bidens flower.
Syritta pipiens

References


Smithsonian (5/99). True flies (Diptera). Retrieved from https://www.si.edu/spotlight/buginfo/true-flies-diptera

Wikipedia (10/21/18). Flies. Retrieved from https://en.wikipedia.org/wiki/Fly

McAlister, E.M. (2017) The Secret Life of Flies. London: Natural History Museum

Eaton, E.R. & Kaufman K. (2007) Field Guide to Insects of North America. New York: Hilstar Editions L.C.

Walliser, J. (2014) Attracting Beneficial Bugs to Your Garden. Portland, OR: Timber Press, Inc.

My photos were so graciously identified by these brilliant people at BugGuide.net. Great thanks and appreciation for your time and expertise!:

Peleteria sp. identified by John F. Carr at https://bugguide.net/node/view/1601495

Syritta pipiens identified by Bill Dean at https://bugguide.net/node/view/1606160

Cylindromyia interrupta identified by John F. Carr at https://bugguide.net/node/view/1606016

Cuterebra sp. identified by Ken Wolgemuth at https://bugguide.net/node/view/1600939

Helophilus fasciatus identified by Ken Wolgemuth at https://bugguide.net/node/view/1599743

Tachina sp. identified by Ken Wolgemuth at https://bugguide.net/node/view/1599741

Muscidae sp. identified by John F. Carr at https://bugguide.net/node/view/1599738

Additional Resources:

Joe Gardener Podcasts:

049-When Good Bugs Eat Bad Bugs: The Business of Beneficial Insects

050-Organic Pest Control: Beneficial Insects And Beyond

067-Predatory Beneficial Insects: Feared Foes of Garden Pests, Pt. 1

068-Top Predatory Beneficial Insects and How to Attract Them, Pt. 2

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Joe Dlugo photographing bees on a tallgrass prairie

Joe Dlugo

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