Syrphid flies, also known as hover flies, or flower flies, are often overlooked, but these small beneficial insects are worth attracting to any garden.
An important component of organic gardening is being aware of predator and prey relationships among the leaves and flowers. Our vegetable gardens and orchard were newly planted this year, and as such are somewhat out of balance in regards to the insects that inhabit those areas, with crop-damaging prey species currently far outnumbering available predators, but we are beginning to see a shift in our favor.
Lots of tender green growth in the vegetable gardens earlier this summer resulted in hoards of aphids on a number of our plants from dill to lettuce to sorrel, but fortunately one of the natural enemies of aphids, are certain species of Syrphid Flies.
Syrphids are distributed globally, and can be found on every continent, except Antarctica. Most Syrphids range from 5-25mm in length. Identification of Syrphid fly species however can be very challenging, as there are more than 200 genera, encompassing over 6,000 species worldwide. They are excellent mimics, as most species have spots or stripes in yellow and brown. Some Syrphid Flies can be quite hairy, and closely resemble bumble bees or honeybees, whereas others appear to more closely resemble wasps. A key distinguishing feature however is that all Syrphids only have a single pair of wings. Syrphids also cannot sting, so although at first glance they may appear menacing based on coloration, they are in fact harmless to gardeners. Just remember that Syrphid Flies are the good guys!
Adult Syrphid Flies are important garden pollinators, feeding on the nectar and pollen of numerous plant species. Although they are technically flies, in some areas Syrphids may actually be more efficient than other native pollinator bee species.
The larval offspring of some species feast on decaying plant and animal matter. Most importantly for us, the larva of some Syrphid species will preferentially gorge themselves on soft-bodied insects such as aphids and thrips.
Many local organic lettuce producers now rely heavily on Syrphid Fly populations as a key method of controlling aphids on lettuce crops. This is because a single Syrphid fly larva can literally consume hundreds of aphids in a month!
Considering our own plague of aphids this year, we’d obviously like to attract more aphid-eating Syrphid Flies. The following clip from Utah State shows a Syrphid Fly larva feasting on an aphid.
The two most important things that Syrphids require in the garden are food, and shelter.
Beyond the herb and vegetable gardens we’re emphasizing plantings of California native plant species. Certain species of California natives are host to specific species of aphids, and thus in turn can attract particular aphidophagus (aphid eating) Syrphid Flies.
For example, our California wild lilacs (Ceanothus thyrsiflorus) attract the Aphis ceanothi aphid, a larval food source for Allograpta, Toxomerus, and Ocyptamus sp. Syrphid Flies.
Our California poppies (Eschscholzia californica) are reported to attract aphids that are appealing to the larva of Sphaeophoria, Syrphus, and Toxomerus sp. Syrphids.
California honeysuckle (Lonicera hispidula) hosts the honeysuckle aphid Hyadaphis tataricae, and our recently acquired California Coffeeberry (Rhamnus californica) attracts the Macrosiphum rhamni aphid.
Although you don’t necessarily have to know which plant attracts which aphid or Syrphid, this does illustrate how plant choice influences which species of beneficial insects may appear in your own gardens, and highlights the importance of planting a diverse array of species in the garden.
As the adult Syrphids feed on nectar and pollen, including plant species that are attractive food resource plants for the adult flies is also important. Some California natives known to attract adult Syrphids include California Buckwheat (Eriogonum fasciculatum), White sage (Salvia apiana), Goldenrod (Solidago californica), and Yarrow (Achillea millefolium).
Non-natives that are useful for companion planting or inter-planting between vegetable crops include sweet alyssum, coriander, fennel, and mustards.
Numerous culinary herbs also are highly attractive to Syrphid flies, including mint, oregano, lemon Verbena, and culinary sage.
Although the presence of appropriate and sufficient food resources are important for attracting Syrphids, it’s also important to recognize that adult Syrphid Flies also need shelter. Studies have shown that Syrphid Flies won’t fly in strong winds, so it’s advantageous to plant windbreaks, not only to protect plants directly from wind damage, but also to provide shelter for adult Syrphid Flies during periods of inclement weather. Here we’re fortunate to be down in a deep valley surrounded by tall trees, so our gardens are very rarely affected by strong wind gusts.
In addition to food and shelter, it is imperative to restrict or eliminate the use of insecticides to control other pests in the garden, including products approved for use in organic production, such as Spinosad (Entrust®) to control leaf miners or sawfly, as such products will interfere with Syrphid Fly activity in the garden.
Next time you see a small bee-like visitor to your garden, take a closer look…it may turn out to be a beautiful and beneficial fly!
For much more about Syrphid Flies, see:
- Flower Flies (Syrphidae) and Other Biological Control Agents for Aphids in Vegetable Crops (ANR Pub 8285)
- Image of Syrphid Fly Larva (UC-IPM)
- Lifecycle of Syrphid Flies (UC-IPM)