Written by Amy Yarger, Butterfly Pavilion Horticulture Director
If I were to come up to you and say, “I’m planting a garden that attracts flies!”, what would you do? Would you back away slowly from me? Envision a trash dump? Flies are usually perceived as dirty, annoying insects, but there are over 16,000 species of flies in North America, and many of them perform important services for us. After bees, flies are the most significant pollinators of crops and native plants. (And, yes, I’m saying that even though I work for Butterfly Pavilion!).
Flies don’t sting like bees or ingest defensive toxic chemicals like butterflies, so how do they defend themselves? If you are a drone fly, you adopt the look and behavior of something scarier, in this case, a honeybee. You probably have seen drone flies in your garden without even realizing it – they are about the same size and shape of honeybees but have only 1 pair of clear wings instead of 2. Another good way to tell these two insects apart is to look at the eyes. Drone fly eyes cover much more of the head, and in the case of males, meet in the middle. Like honeybees, drone flies are adaptable in terms of habitat and may be spotted in grasslands, wetlands, urban gardens and roadsides across western North America. They are most active in the late spring through summer, but a few may survive into the early fall if the weather is mild enough.
These flies not only look like honeybees, but they produce a “buzzing” sound to fool potential predators as well. However, drone flies are also called “hover flies”, and their flight is quite distinctive – more like tiny helicopters than airplanes. The female’s first meal when she emerges in the spring is protein-rich pollen – this will give her the resources she needs to produce and lay eggs. From then on, they visit a wide variety of flowers for nectar, but especially members of the sunflower and carrot families. That means you are likely to see them on black-eyed Susans, zinnias, yarrow, fennel, and dill. Plentiful nectar fuels them in the search for mates and a good egg-laying spot.
The larvae of the drone fly are aquatic, so favorite egg-laying spots will be shallow pools, ponds and ditches, especially if there’s some decaying organic material nearby. No one said that child-rearing was pretty! The larvae have a breathing tube from their posterior end and are often called the glamorous name of “rat-tailed maggots”. They extend these appendages to the water surface and can be found in different depths of the water depending on time of day and food availability. Once they are ready to metamorphosize, they’ll find a drier spot in the soil and pupate for 8-10 days. There may be 2-3 generations of these pollinators in a year, with the final generation of the year overwintering as an adult fly.
Because of their amphibious lifestyle, water quality is especially important for the health of these pollinators. Avoiding chemical use will prevent polluting runoff that can endanger hover fly babies. Participating in stewardship projects that restore wetlands will also ensure that these animals always have plenty of places to raise their young. In your own garden, maximizing native plant diversity creates the niches that these shy and unassuming pollinators need to live. Plants with flat clusters of white or yellow flowers are especially attractive to hover flies. You may have thought that you never wanted to help a fly, but our gardens and farms depend upon them. Maybe you’ll be the first on your block to plant a habitat for drone flies?
Want to learn more about pollinators and how to help them? Contact Butterfly Pavilion’s horticulture department at firstname.lastname@example.org!