Hoverflies
Hoverflies are true flies — one pair of wings, no sting — that are often mistaken for bees or wasps because of their yellow-and-black bands. The adults feed on nectar, pollen and honeydew and are useful pollinators. In about 40% of British species the legless, slug-like larvae hunt aphids, each eating roughly 100–400 before it pupates. Pupae are sold for commercial greenhouses, but in a garden you keep them by growing open flowers and not spraying.
At a glance
- Kind
- Wild — attracted, not bought
- Adult
- 4–25 mm; one pair of wings
- Larva
- Legless maggot, 5–20 mm
- Eats
- ~100–400 aphids per larva
- Egg to adult
- 2–4 weeks in the growing season
- Adults feed on
- Nectar, pollen, honeydew
How it works
A female that has fed on pollen and nectar lays grey-to-white eggs about 1 mm long, usually singly, among aphid colonies. The larva that hatches has no legs and tapers towards the head; it moves through the colony like a small slug, pierces aphids with its mouth hooks and sucks out the contents. When full-grown it pupates in a hardened, teardrop-shaped case.
Egg to adult takes two to four weeks in the growing season, and the aphid-eating species can have five to seven generations a year. Not every hoverfly is a predator: the larvae of drone flies (Eristalis) are rat-tailed maggots that live in liquid manure and similar wet, decaying matter, and the bulb flies (Merodon, Eumerus) feed inside daffodil and other bulbs. In Britain about 40% of hoverfly species have aphid-eating larvae.
What it is confused with
Hoverflies are built to be mistaken for something that stings. The larva, which does the aphid control, is easy to mistake for a pest.
- Also goodHoney bees and bumblebees — Bees have two pairs of wings; a hoverfly has one pair, and it cannot bite or sting.
- Also goodGreen lacewing larva — Also hunts in aphid colonies, but it has distinct legs and an alligator shape; a hoverfly larva has no legs at all.
- PestSmall caterpillars — A hoverfly larva has no true legs at all and tapers towards the head; a small larva walking on legs at the front is something else, often a caterpillar.
- PestNarcissus bulb fly — A hairy, 15 mm hoverfly that looks like a small bumblebee, around daffodils from mid-May to June; its larvae hollow out the bulbs.
How to keep it around
Adult hoverflies feed on nectar, pollen and honeydew, and the females need this food to produce viable eggs. They are short-tongued, so they do best on open flowers where pollen is easy to reach. Plant a spread of these so something is in bloom from spring to autumn, and keep insecticides away from colonies the larvae are working.
- Sweet alyssum (Lobularia maritima) — one of the flowers UC IPM lists for intercropping with lettuce to feed syrphids
- Spring: guelder rose (Viburnum opulus), with flat, open flower heads, plus aubrieta and cow parsley
- Summer: blackberry, fleabane (Erigeron) and yarrow
- Autumn: ivy, California poppy and asters
- Phacelia and heather, plus alliums, coreopsis, Japanese anemone, buddleja, calendula, hebe, poppies, Sanguisorba, thistles and angelica from the RHS list
- No insecticide sprays on plants where hoverfly larvae are working an aphid colony
Pesticide sensitivity
Spinosad, allowed in organic growing, suppressed syrphid larvae so badly in lettuce trials that the treated heads were unsaleable with aphids. Broad-spectrum pyrethroids, organophosphates and carbamates kill natural enemies too. Open the compatibility matrix →
When to choose something else
Hoverflies are the best free aphid control a garden has, but they cannot be ordered to a garden. Look elsewhere when:
- The crop is under glass or indoors — you cannot count on wild adults finding it; hoverfly pupae are sold for greenhouses, or use Aphidius colemani
- You need knockdown on a colony now — lacewing larvae can be bought and put straight onto it
- The pest is mealybug on a houseplant — use the mealybug destroyer
- Hairy, bumblebee-like flies are circling your daffodils from mid-May to June — that is the narcissus bulb fly, a pest hoverfly
Hoverflies by target
What it eats and when it turns up differ by pest. Each page below is the picture for one target.