Recently, I wrote aphids invaded our ash trees, but I’m pleased to report a battalion of good little buggers came to the rescue. I’m referring to the syrphid flies, sometimes called flower flies or hoverflies. The small adults feed on nectar, pollen and the honeydew produced by aphids and other sucking insects. While adults are not predators, the larvae eat aphids, scale insects and thrips. Each larva can eat hundreds of aphids in a short period of time. They can reduce aphid infestations rapidly. An added benefit to these hard-working critters is they’re also good pollinators.
Larvae are yellowish, legless and blind and look like maggots. “Its mouth has a triple-pointed dart with which it seizes and pierces its prey before sucking it dry” (Warner, 2018. Washington State University). Adults look like small bees with flattened bodies. However, they’re not bees, they’re flies, with just one pair of wings rather than the two bees or wasps have. These yellow and black creatures, which are 3/8 to 1/2 inch long, don’t sting. Their fast and agile flying resembles that of hummingbirds, and like hummers, they too hover and dart over and around plants. Their life cycle from egg to larva to adult takes two to four weeks to complete.
Adult syrphid flies need pollen from wildflowers or weeds to produce eggs. The population in my yard is thriving in an area where I’ve let assorted wildflowers reseed over the last few years. I unwittingly provided the perfect food sources for both adults and larvae because the flowers are located under the aphid-infested ash trees. I also was lucky in supplying them the perfect habitat, since syrphid flies overwinter as larvae in leaf litter and lay their eggs near or in aphid colonies. Where I’m seeing multitudes of these flies hovering over the wildflowers is next to a huge perennial leaf pile. There are so many flies in that area it sounds like a buzzing bee hive. I love walking through the flowers, watching and listening to the flies. They’re quite busy!
Fortunately, I never use insecticides to control aphids, which is good for the syrphid flies. They’re highly susceptible to insecticides. The size and activity of this population of flies in my yard reminds me why I cultivate wildflowers, why I don’t use insecticides, and how important beneficial insects are to integrated pest management as well as pollination.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita, University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.