The presence of syrphid flies, also called hoverflies, is a welcome sight in agricultural landscapes. Syrphid flies contribute to pollination, pest suppression, and decomposition. There are four subfamilies of syrphids: Pipizinae, Eristalinae, Microdontinae, and Syrphinae. Larvae from the Eristalinae subfamily act as recyclers, feeding on decaying organic matter. The Pipizinae subfamily includes species whose larvae feed on root aphids, helping with the control of below-ground pests. Microdontinae is unique among syrphids as their larvae are myrmecophilous, living in ant nests and feeding on ant broods. The Syrphinae subfamily, the focus of this article, are natural enemies of soft-bodied insects, particularly aphids, and are the ones mainly encountered in vegetable fields and high tunnels in Indiana!
Although the bright and colorful patterns on the adults may lead to confusion with bees and wasps, syrphid flies are true flies (Order Diptera), possess two wings and short antennae. They undergo complete metamorphosis (Figure 1), transitioning from egg to larva, pupa, and adult. The larvae may sometimes be confused with those belonging to the Cecidomyiidae family, aphid predatory midges. However, syrphid larvae are less brightly colored, appear segmented, and lack chewing mouthparts (Figure 2). Syrphids lay their eggs (Figure 3) near aphid colonies or flowers. Eggs hatch and feed on soft-bodied insects, such as aphids, as they progress through several larval stages. When they are done feeding, they pupate either in the soil or on the plant (Figure 4).
Figure 1. Syrphid fly lifecycle (design by Sheyla Zablah).
Figure 2. The larva of a predatory midge fly Cecidomyiidae (top panel) and a syrphid fly (bottom panel) (Photos by John Obermeyer).
Figure 3. Syrphid larvae (Photos by John Obermeyer).
Figure 4. Eupeodes americanus larva (panel a; photo by Allison Zablah), pupa and adult (panel b) (Photo by John Obermeyer).
There is a wide variety of syrphid species in Indiana (Figure 5), which can be found throughout a variety of habitats, from cornfields to gardens and forests. We typically observe syrphid flies in late spring and summer. In fact, we can confirm their presence in our research high tunnels since late April. As our field season begins, we have noticed syrphid flies, specifically Eupeodes americanus, on spinach crops from a fall planting in high tunnels, where aphids were present, typically finding 2-3 larvae per plant. In addition to monitoring the crops at our research farm, we visit other farms. During these visits, a lot of Toxomerus marginatus adults (Figure 6) are present, especially where polyculture and flowers, such as sweet alyssum, are being grown.
Figure 5. Syrphid fly adults pollinating a variety of flowers (Photos by John Obermeyer).
Figure 6. Toxomerus marginatus adult (Photo by John Obermeyer).
Understanding and promoting the presence of syrphid flies in agricultural settings can enhance crop pollination and pest control, making them valuable allies in sustainable farming practices. This is one insect you want to have around, even if they do bother you in late summer when hordes of them land on your body for a sip of sweat!