Hover flies have a characteristic flight pattern – hovering in one spot, moving suddenly forwards or sideways, then hovering again. They are actually members of a fly family that have evolved as wasp and bee mimics. They are important as pollinators of plants.
Some people mistake hover flies for wasps or bees because of their black and yellow-striped abdomens and also because they can occur in huge numbers.
Why do hoverflies look like honeybees?
The adult flies’ mimicry of various wasps and bees is because (though quite harmless) they get some protection from would be predators, like birds, by copying the bold yellow and black warning colours of their genuine stinging models.
An obvious question for most people is how to distinguish between a hover-fly and a wasp or bee? This can prove difficult without some knowledge of insect behaviour and morphology, but perhaps the most obvious difference (if you can get close enough!) is that hover-flies, like all Diptera, have only one pair of wings, whereas wasps and bees have two pairs.
Aphid-eating hover-fly larvae are rather flattened, legless and maggot-like. Most are greenish or brownish in colour and well camouflaged, and largely go unnoticed as they crawl over foliage in search of their aphid prey.
Hover flies have large heads, large eyes, and small or inconspicuous antennae. Their bodies are medium to slender, with a waist that is not significantly narrow, unless it is a wasp mimicking species. They have one pair of clear wings, and the banded forms have yellow and black bands of equal width. They are small to medium sized flies, with an average body length of 1-1.5cm.
Habitat and Biology
Hover fly mimicry of wasps can include having a warning coloration of yellow and black, a narrow waist like a wasp and even the ability to mimic the stinging action of a wasp, by pushing the tip of the abdomen into your fingers if they are caught and held. However, they do not sting and are quite harmless.
Hover flies may appear in large numbers during hot weather. They linger in gardens to feed at flowers and to seek shade. Many species perform the useful role of ridding the garden of aphids, as they lay their eggs in aphid colonies and the larvae (maggots) feed on the aphids. Aphid-eating hover fly larvae are flattened, legless and maggot-like. Most are green or brown in colour, going largely unnoticed as they crawl over foliage in search of their aphid prey.
Some hover fly species (Eristalis sp) lay their eggs in stagnant water. These aquatic larvae have a long thin breathing tube – hence the common name, “rat-tailed maggots”. Another hover fly species (Microdon sp) has a larval form that scientists originally classified as a mollusc because it looks rather like a small slug. Microdon larvae survive by scavenging in ant nests, mimicking the ants’ chemicals in order to escape detection by their hosts.
A typical adult Hover-fly (Syrphus)
Hoverflies belong to the family Syrphidae, within the large order of insects called Diptera, and most are easily recognised by their generally bright colours and hovering ability. The adult flies spend much of their life on flowers, feeding on pollen and nectar, and thus play an important role in the pollination of many wild and cultivated plants.