Hover Flies
Syrphidae
predator-pollinator · aphid predator · conservation
Last updated
Hover flies serve a dual role as both predators and pollinators. The larvae are legless, slug-like maggots that feed voraciously on aphids, consuming 400 to 1,000 aphids during development. Adults are strong fliers easily recognized by their hovering flight and bee-mimicking coloration, and they are important pollinators of crops and wildflowers.
Over 300 species occur on the West Coast of North America, with multiple generations per year in the mild Puget Sound climate. Hover flies are strictly conservation biocontrol agents. Adults depend on nectar and pollen throughout their lives, so continuous bloom from early spring through fall is essential to sustain populations. Apiaceae (dill, fennel, cilantro) and Asteraceae (yarrow, tansy) are particularly effective insectary plantings.
Target Pests (29)
- Aphid
- Apple rust mite
- Balsam woolly adelgid
- Black cherry aphid
- Blister mite
- Cyclamen mite
- Dryberry mite
- Eriophyid mite
- False spider mite
- Filbert Aphid
- Hawthorn aphid
- Lecanium scale
- Pear rust mite
- Pearleaf blister mite
- Poplar Petiole Gall Aphids
- Prunus rust mite
- Raspberry beetle (aka Western raspberry fruitworm)
- Redberry mite
- Redhumped caterpillar
- Scale insect
- Spider mite
- Spruce aphid
- Syneta beetle
- Tent caterpillar
- Thrips
- Twospotted spider mite
- Walnut Aphid
- Western flower thrips
- Woolly apple aphid
Quick Reference
Lifecycle & Phenology
Complete metamorphosis: egg, three larval instars, puparium, adult. Females deposit single elongate white eggs on plant surfaces near aphid colonies. Eggs hatch in 2-4 days. Larvae feed through three instars over 7-10 days, consuming hundreds of aphids. Pupation occurs in a teardrop-shaped puparium on leaf surfaces, in soil, or in leaf litter, lasting 8-10 days. Adults emerge and require 3-5 days of pollen feeding before eggs mature. Adults are important pollinators, feeding on nectar and pollen from open-structured flowers, especially Apiaceae, Asteraceae, and Brassicaceae. Multiple overlapping generations per year in PNW. Most species overwinter as pupae in soil or leaf litter, though some overwinter as larvae or adults (Gilbert, 1993; Schneider, 1969).
| Generations per Year | 3-7, depending on species and temperature; continuous overlapping generations in mild maritime PNW summers (Gilbert, 1993) |
| Overwintering Stage | pupa |
| Egg Capacity | 2,000-4,500 eggs per female lifetime for *Episyrphus balteatus*; most species 500-1,500 (Branquart & Hemptinne, 2000; Tenhumberg & Poehling, 1995) |
| Larval Duration | 7-10 days through three instars at summer temperatures (Tenhumberg & Poehling, 1995) |
| Development Duration | 17-28 days egg to adult at 20-25°C (Gilbert, 1993) |
| Adult Lifespan | 20-45 days (Gilbert, 1993); pollen-fed females live significantly longer than sugar-only females |
| Active Months | March through November; adults observed into late fall in mild PNW autumns |
Habitat & Conservation
Nectar & Pollen Sources
Pesticide Sensitivity
| Product Class | Impact | Notes |
|---|---|---|
| Neonicotinoids imidacloprid, clothianidin, thiamethoxam | lethal | Systemic presence in nectar and pollen is lethal to pollen-feeding adults; larvae exposed through contaminated aphid prey (Xerces Society, 2016) |
| Pyrethroids bifenthrin, permethrin, lambda-cyhalothrin | lethal | Broad-spectrum contact toxicity; residual activity kills larvae feeding on treated leaf surfaces for 2-4 weeks (PNW Insect Management Handbook) |
| Organophosphates malathion | lethal | Highly toxic to all life stages on contact (PNW Insect Management Handbook) |
| Spinosad spinosad | moderate | Toxic to larvae on wet contact; reduced risk after drying (Xerces Society, 2016) |
| Horticultural oils mineral oil | low | Direct contact only; minimal residual. Low impact on adults; may smother eggs and small larvae if directly contacted (UC IPM, 2024) |
| Insecticidal soaps potassium salts of fatty acids | low | Contact only; no residual. Low risk to adults after drying (UC IPM, 2024) |