This is “National Pollinator Week” (June 17 – 24). The non-profit “Pollinator Partnership” conceived the idea in 2007 to encourage groups and communities to hold celebrations and awareness campaigns highlighting the importance of pollinators. That same year, the U.S. Senate designated the third week of June to be the official celebratory week for the recognition of pollinators.
Following are quotes about Pollinator Week taken from websites found using the search words “pollinator week”:
- Duke Garden: “… a celebration of the amazing creatures—butterflies, bees, birds, beetles and more—that form the backbone of our natural and agricultural ecosystems.”
- Farmers for Monarchs: “… an international celebration, promoting the valuable ecosystem services provided by bees, birds, butterflies, bats, beetles, moths, wasps, and flies.”
- Pollinator Partnership: “Pollinator Week has now grown into an international celebration, promoting the valuable ecosystem services provided by bees, birds, butterflies, bats, beetles, moths, wasps, and flies”
My intention is not to embarrass anyone or any organization. However, you’ll note that flies, which belong to the order Diptera, the second most important order among flower-pollinating insects worldwide, are commonly excluded from lists of pollinators or relegated to the back of the line. If the listings reflected the true significance of flies as pollinators, they would be in front of moths, butterflies, and beetles.
The Proper Order of Things
Research has shown that the vast majority of insect pollinators belong to four insect orders. They are listed in descending order from the most to the least number of pollinators: (1) Hymenoptera (bees and wasps), (2) Diptera (flies), (3) Lepidoptera (moths and butterflies), and (4) Coleoptera (beetles).
People are seldom surprised that bees and wasps are the top pollinators. They’re more glamorous and have enjoyed wonderful P.R. campaigns. However, learning that flies are more important than butterflies and moths as plant pollinators often surprises people. It certainly surprised me. We plant gardens dedicated to butterflies!
When the current interest in pollinators began to take shape, I decided to focus on taking pictures of pollinators to aid in my teaching. Using sock puppets to teach about insects only goes so far. However, my shots were consistently spoiled by Common Green Bottle Flies (Lucilia sericata, family Calliphoridae) buzzing the flowers. I began calling them the “green photo-bombing flies.”
However, eventually, another neuron fired sparking me to ask myself, “Why are green bottle flies so common on flowers?” The answer is found in the literature cited at the end of this Alert.
A literature review (Cook et al.) revealed that worldwide, the most frequent flies observed visiting flowers were members of three dipteran families: Calliphoridae, Rhiniidae, and Syrphidae. Rhiniidae are “nose flies” so named because the lower part of their face protrudes like a nose. Most species are found outside of the U.S.
Flies in the Calliphoridae family are commonly called blow flies, bluebottles, or greenbottles. This family includes my green photo-bombing fly. Calliphorids also provide other valuable ecological services beyond plant pollination. They are part of the cleanup crew converting carrion and dung into nutrients that flow back into the soil. Without these flies, we could be up to our necks in … well, we won’t go there.
Members of the Syrphidae family commonly mimic bees. Indeed, perhaps cases of mistaken identity could cause the uninitiated to lump syrphid flies with bees during observational “insect pollinator counts.”
To separate flies from bees, count the number of wings. Flies (Diptera) have two wings (Di- = two; -ptera = wings) while bees and wasps (Hymenoptera) have four wings.
Most flies are good flyers which is why they’re called flies. Syrphid flies are exceptional fliers capable of hovering in place which is why they’re called “hover flies.”
Hover flies also play a significant role in our landscapes beyond being important plant pollinators. Their larvae are predators, so they provide a twofer. Unlike most fly larvae (= maggots) that look like animated rice, hover fly larvae are active hunters preying upon other insects, most often aphids. In other words, planting a pollinator garden that attracts hover flies also makes it a pest management garden reducing the need to use insecticides.
On a side note, there is a common misconception that plagues flies as pollinators: they only visit flowers that smell like rotting meat. While it’s true that some plants produce foul-smelling flowers to draw flies, the vast majority of flowers visited by flies don’t stink.
For example, hydrangeas (Hydrangea spp.) are a fly favorite; however, I’ve never sniffed a rotten-smelling hydrangea bloom. The same is true for roses (Rosa spp.), mountain mints (Pycnanthemum spp.), maples (Acer spp.), lindens (Tilia spp.), etc., etc.
American Pawpaw (Asimina triloba) is commonly tagged as a flycatcher which is partially true, but not because the flowers smell like rotting meat. In a paper published in 2006, the researchers reported that the floral scent chemistry of odors wafting from pawpaw flowers match the chemistry of odors arising from fermentation. Personally, I like the smell of fermentation, and growing up in my native West Virginia, the yeasty odor wafting through the hills and hollows smelled like money. But that’s another story.
Lord of the Flies?
As noted above, there was a time when I did not know that flies are important plant pollinators and there are many cautionary quotes about the zeal of the recently converted. But I’m not delusional despite occasional evidence otherwise. It’s a tough sell to get people to accept that flies deserve a place of honor in the pollinator parade lineup.
Let’s face it, flies are not as glamorous as butterflies and moths, or as charismatic as bees. I recognize that it’s highly unlikely flies will topple a monarchy; it’s doubtful we’ll ever see “Fly Gardens.”
However, “Pollinator Week” is about raising awareness of the importance of plant pollinators. This Alert aims to highlight the value of flies as pollinators. They should not be relegated to last on the list of important pollinators or ignored altogether. Ignoring flies neglects important threads woven into the tapestry that tell the story of how insects affect our lives and environment.
Selected References (Listed by Publication Dates)
Larson, B.M.H., Kevan, P.G. and Inouye, D.W., 2001. Flies and flowers: taxonomic diversity of anthophiles and pollinators. The Canadian Entomologist, 133(4), pp.439-465.
Goodrich, K.R., Zjhra, M.L., Ley, C.A. and Raguso, R.A., 2006. When flowers smell fermented: the chemistry and ontogeny of yeasty floral scent in pawpaw (Asimina triloba: Annonaceae). International Journal of Plant Sciences, 167(1), pp.33-46.
Ssymank, A., Kearns, C.A., Pape, T. and Thompson, F.C., 2008. Pollinating flies (Diptera): a major contribution to plant diversity and agricultural production. Biodiversity, 9(1-2), pp.86-89.
Woodcock, T.S., Larson, B.M., Kevan, P.G., Inouye, D.W. and Lunau, K., 2014. Flies and flowers II: floral attractants and rewards. Journal of Pollination Ecology, 12, pp.63-94.
Inouye, D.W., Larson, B.M., Ssymank, A. and Kevan, P.G., 2015. Flies and flowers III: ecology of foraging and pollination. Journal of Pollination Ecology, 16, pp.115-133.
Rader, R., Bartomeus, I., Garibaldi, L.A., Garratt, M.P., Howlett, B.G., Winfree, R., Cunningham, S.A., Mayfield, M.M., Arthur, A.D., Andersson, G.K. and Bommarco, R., 2016. Non-bee insects are important contributors to global crop pollination. Proceedings of the National Academy of Sciences, 113(1), pp.146-151.
Orford, K.A., Vaughan, I.P. and Memmott, J., 2015. The forgotten flies: the importance of non-syrphid Diptera as pollinators. Proceedings of the royal society B: biological sciences, 282(1805), p.20142934.
Raguso, R.A., 2020. Don’t forget the flies: dipteran diversity and its consequences for floral ecology and evolution. Applied Entomology and Zoology, 55(1), pp.1-7.
Cook, D.F., Voss, S.C., Finch, J.T., Rader, R.C., Cook, J.M. and Spurr, C.J., 2020. The role of flies as pollinators of horticultural crops: An Australian case study with worldwide relevance. Insects, 11(6), p.341.
Dunn, L., Lequerica, M., Reid, C.R. and Latty, T., 2020. Dual ecosystem services of syrphid flies (Diptera: Syrphidae): pollinators and biological control agents. Pest management science, 76(6), pp.1973-1979.
Goodrich, K.R., Ellis, I., DeHaas, A., Senski, R. and Savage, J., 2023. False Advertising with Fermented Scents: Floral Mimicry in Pawpaw (Asimina triloba: Annonaceae) Pollination. International Journal of Plant Sciences, 184(6), pp.485-497.
