Feeding the Flower Flies: How to Attract Flies to Your Garden

When asked to describe insect species that can pollinate flowers, most people think of bees, butterflies, moths, and hummingbirds. However, flies are critical pollinators in both natural and agricultural systems. A recent analysis of crop species found that flies visited 72% of the 105 crops studied (bees visited 93%). In some cases, flies can provide more consistent pollination in early spring than bees, likely because they are often active at cooler temperatures.

Like bees, adult flies visit flowers to feed on the nectar (as a source of carbohydrates) and pollen (as a source of protein and fats). However, while bees actively collect pollen to bring back to their nest to feed larvae, flies do not provide maternal care and passively transport pollen on their bodies as they visit different flowers.

While many different types of flies visit flowers, one of the most commonly observed is adult syrphid flies (in the family Syphridae), also known as “flower flies." These flies have been recorded visiting over 50 different crop species. They often resemble bees with yellow and black striped bodies. However, they have a distinctive flight pattern, and because of this pattern, they are often called “hover flies." There are more than 6,000 described species of flower flies in the world and over 400 in the northeastern US alone.

Like bees and butterflies, flies exhibit complete metamorphosis, moving from egg, larvae, pupae, and finally to adult. Larval flies from different syrphid and tachynid species lead surprisingly exciting and diverse lives. Many species are predators, feeding on insects such as aphids and scales, thus providing biological control of pests. Others help to break down organic matter, thereby releasing nutrients back into your garden.

Flies are attracted to a variety of flowering plants. As a rule of thumb, flies tend to prefer white flowers with open structures that are easy to access. Often these flowers have scents that are not necessarily floral but resemble decomposing material. A thirty-three-year data set on plant-pollinator interactions, generated by Charles Robertson in Illinois, found that syrphid and tachinid fly species visited 257 species of flowering plants from 57 families, and they preferred species in the Asteraceae, Rosaceae, and Apiaceae families.

To attract flies to your garden, plant a diversity of flowering plant species from these preferred species, selecting species that bloom throughout the year. More information can be found on the Penn State Master Gardener's Pollinator Garden Certification Program site. Additionally, Rutger's Protecting Bees site has a tool that you can use to find plants that specifically attract flies. Tooker et al. (2006) also provides a list of the plant species in Robertson’s data set that are most attractive to flies.

Because of their diversity of lifestyles and the overall lack of research in fly ecology, we know little about what types of habitats best support fly populations. They tend to favor environments with adequate humidity and access to water, such as riparian areas, meadows, and forest openings. To encourage flies and other insect species in your backyards, consider a mixed planting system that creates different microhabitats; include decomposing materials like leaf litter or other organic matter. Insecticides used to control pests can negatively affect fly species, so an integrated pest management approach is recommended to reduce off-target effects.

With their diversity of forms, lifestyles, and ecological services that they provide, flies can be both fascinating and rewarding visitors to your garden.  

Acknowledgments

Many thanks to Michael Skvarla and Natalie Boyle for comments and discussion.

References

Kudo, G., Ida, T. Y., and T. Tani. “Linkages between phenology, pollination, photosynthesis, and reproduction in deciduous forest understory plants" Ecology 89(2): 321-331. (2008)

Tooker, J.F., Hauser, M., and L.M. Hanks. “Floral Host Plants of Syrphidae and Tachinidae (Diptera) of Central Illinois" Annals of the Entomological Society of America. 99(1): 96-112 (2006)

R. Rader, Cunningham, S.A, Howlett, B.G. and D.W. Inouye. “Non-Bee Insects as Visitors and Pollinators of Crops: Biology, Ecology and Management" Annual Review of Entomology. 65:20.1–20.17  (2020)

Skevington, J.H., Locke, M.M., Young, A.D., Moran, K., Crins, W.J., Marshall, S.A. “Field Guide to the Flower Flies of Northeastern North America" Princeton University Press.  511 pp.  (2019) 

Wilmer, P.  “Pollination and Floral Ecology" Princeton University Press.  832 p.  (2011)