Hover flies, Syrphidae |
There are 6 000 species of hoverfly world wide, and 266 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. Mimicry in hoverfliesMany 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 behaviourMany 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. Hover fly eggsThe 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. |
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Hover fly larvaeOn 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. |
Eristalis tenax, the rat-tailed maggot, Drone flyOn the right is the rat-tailed maggot, Eristalis tenax the adult, above, 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 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. 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. 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. |
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Eristalis horticolaOn 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 arcuatumThis species (right) is frequently found in Scotland, but less common elsewhere. The adult flies from May to September, and is most common near woodlands. |
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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. Uaually 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. |
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Criorhina berberinaOn 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.
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On the left is Syritta sp., a hover fly larva that is found in rotting debris. |  |
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. |
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The photograph on the left shows mate seeking behaviour. The male hoverfly generally has two strategies in seeking a mate.
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