Hover flies, Syrphidae

Hoverflies overview

There are 6,000 species of hoverfly world wide, and 276 species in the U. K. The adults are often brightly coloured attractive flies. Note the the aristate antennae and huge eyes typical of the more "advanced" flies.

Hover fly larvae

On the left is an aphid-eating hoverfly larvae. It has stuck the skins of sucked-dry aphids to its body - they are the little white things on the centre of its body. A larva like this can eat 50 aphids a day.

When the larva pupates the pupa is brown and stuck to the plant.

hoverfly larva

Hover fly eggs

The eggs are usually white. Eggs that hatch into carnivorous larvae are usually glued singly to plants amongst or near their prey. Eggs of non-carnivorous species are usually laid in batches on or near the larval food.

Mimicry in hoverflies

Many hoverflies mimic the colouration and/or hairiness of social bees and wasps. This enables them to avoid attack by predators who believe they might be able to sting. This form of mimicry is termed Batesian mimicry.

Hoverfly food and behaviour

Many Hover fly larvae are slug-like and eat aphids (see below left), others are scavengers.

Adult hover flies feed on pollen and nectar.

Flight speed has been recorded as 3.5 metres per second with a wing beat of 120 per second. Compare this with other insects. Hoverflies are valuable pollinators.

Sericomiya silentis (right)

Sericomiya silentis larvae are the rat-tailed type - see the drawing below. They are found in drainage ditches, peaty pools and bogs.

The adults are found along woodland edges and tracks on flowers when it is sunny. This one was found in Craigmyle woods on scabious in August. Adults fly from May - November. Adult body length is around 16 mm making it one of the largest British hoverflies.

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Sericomyia silentis, adult hover fly

Eristalis tenax, the rat-tailed maggot, Drone fly

Some species of hoverfly are aquatic, and often these are commonly known as rat-tailed maggots. On the right is an Eristalis tenax adult, it is also known as the drone fly, as it resembles a male honeybee. It is found around the world.

The eggs are white, and laid on or near manure or stagnant water.

The maggot's tail (see the drawing below) can be up to 4 times its body length, and the total length can reach 5.5 cm. The tail is a siphon or snorkel of three segments to allow it to breathe underwater, and can be contracted and extended like a telescope. Because it gets its air from the surface it can live in very dirty and polluted water.

It looks a little like a dirty white caterpillar as it does have what appear to be prolegs. It feeds on organic particles. The larva moves to drier areas before pupating.

The adults - both males and females - eat nectar and pollen. Body length is 14 - 16 mm. Apart from the head it really does look like a honey bee.

Eristalis tenax adult Drone fly, Hoverfly

They can be seen year round in warm, sunny weather, but are most common in August and September. They overwinter as adults in cellars, sheds, hollow trees, etc.

Adult males often hover over open areas 2 - 4 m above the ground.

Eristalis larva, rat tailed maggot

Eristalis horticola, hoverfly adult

Eristalis horticola

On the left is an adult Eristalis horticola in its typical habitat of white umbelliferous flowers. It is found throughout the U. K., but is more common in the north.

The larva is similar to Eristalis tenax, above, in that it has a long tail for breathing in poor quality aquatic habitats.

Chrysotoxum arcuatum

This species (right) is frequently found in Scotland, but less common elsewhere. The adult flies from May to September, and is most common near woodlands.

Chrysotoxum arcuatum, adult hoverfly

Syrphus ribesii, Episyrphus balteatus, adult hoverflies, adult marmalade fly

On the left is Syrphus ribesii. Adult body length is 9 - 13 mm. Adults are commonly seen flying from April to October, and is abundant in the U. K. It is found in most habitats, and the adults visit flowers of many types.

It overwinters as a larva in leaf litter. The larva eats aphids.

Episyrphus balteatus, commonly known as the marmalade fly, and is one of the most common hoverflies in the U. K. Adult body length 7 - 11 mm, and wing length 6 - 10 mm. Flies from May to October, but most commonly seen in July and August. It overwinters in the U. K. as an adult, but may not survive very cold winters.

Adult males are territorial, and within the territory will display to females and chase off any other males.

The female lays her eggs on plants where there are aphids.

The larva eats aphids from a wide variety of plants, but seems to have a preference for aphids located lower down on the plant. A single larva will eat around 200 aphids before it pupates. Usually it pupates near the aphid colony.

From egg to adult takes around a month. There are usually 2 generations per year.

Adults feed on nectar, and their favourite flowers are hogweed, cow parsley, ragwort and thistles.

Criorhina berberina

Criorhina berberina

On the left and right is Criorhina berberina, a hoverfly that is often mistaken for one of the ginger bumblebees such as Bombus pascuorum. However if you manage to get a look at its huge eyes and orange antennae there is no mistaking it.

 

Criorhina berberina
Syritta sp. a hover fly larva found in rotting debris On the left is Syritta sp., a hover fly larva that is found in rotting debris. hover fly

The African water lily on its first day of blooming has hundreds of showy stamens and a nice bright flower. This attracts hover flies.

On day 1 in the centre of the flower is a pool of poisonous liquid that looks like nectar. When the hover fly lands on the stamen it falls into this liquid as the stamen are very smooth and overhang the pool. The hover fly cannot climb out as there is nothing to get a grip on. So the hover fly dies in the poisonous liquid.

At night the flower closes and the liquid washes pollen from day two water lilies off the body of the dead hover fly. This pollen fertilises eggs at the bottom of the liquid. On day two it is quite safe for hover flies to visit the lily as the stamens no longer hang over a poisonous pool as the pool has gone. The hover flies will gather pollen on their bodies, but will pay with their lives if they then try to do the same to a day one flower.

hoverfly mate seeking behaviour

The photograph on the left shows mate seeking behaviour. The male hoverfly generally has two strategies in seeking a mate.

  1. He patrols around oviposition sites. The female will have already mated if she is seeking a site to lay eggs. But if the male can persuade her to mate again his sperm will have precedence.
  2. He patrols over flowers. This is shown on the left. He will investigate anything that remotely resembles a female hoverfly bouncing down to get close or even touch the insect. Mating is rarely seen.