Animals

Hoverflies

by Marcia Malory

Hoverflies are flies that have a unique way of defending themselves against predators - they mimic wasps and bees.

Like bees and wasps, many hoverflies have yellow bands on a blackish or a metallic background.

Some hoverflies have dark margins at the front of their wings, which resemble the rolled wings of a wasp.

There are hoverflies with long antennae - these look like the antennae of wasps rather than those of flies.

To complete the deception, most hoverflies will buzz like a bee when cornered.

When birds or other predators see hoverflies, they avoid them, mistaking them for insects that sting.

Hoverfly Syrphus ribesii, photo by Joaquim Alves GasparSyrphus ribesii

The hoverfly species Syrphus ribesii is very common in Europe. It can often be seen hovering near or sitting on flowers between April and November.

Syrphus ribesii is relatively large - about one half inch long with a wingspan of about one inch.

It has a dark abdomen, with three orange-yellow bands and two crescents at its base.

Adult Syrphus ribesii eat pollen and nectar from flowers, while larvae eat aphids.

During mating, the males wait on projecting parts of plants until females to pass. Then, the males fly after the females.

Mating usually occurs on plants.

A female will lay between one and three eggs on an aphid-infested plant.

Each female may lay 100 eggs a day, as many as a thousand all together.

The eggs hatch three or four days after they are laid.

Larvae begin to feed on aphids immediately after they are hatched.

Some ants care for these aphids. These ants feed on a substance known as honeydew that the aphids secrete.

They ants will attack the Syrphus ribesii larvae in order to defend their aphids.

In response, the larvae secrete a slime that deters the ants.

When the larvae are full-grown, after about ten days, they attach themselves to leaves or twigs and become pupae.

Adult flies emerge after about 10 days.

Several generations follow this cycle until autumn.

Once autumn arrives, fully grown larvae hide in the soil until the winter ends. They become pupae in March or April.

Hoverfly Scaeva pyrastri, photo by Joaquim Alves GasparScaeva pyrastri

Scaeva pyrastri is blue-black and has three white markings, known as lunules.

This hoverfly species lays eggs throughout the year.

Males die after mating.

Females live on, hibernating in sheltered places like old trees over the winter.

Hoverfly Marmalade Fly Episyrphus balteatus, photo by Joaquim Alves GasparEpisyrphus balteatus

Episyrphus balteatus, also known as the marmalade fly, also hibernates as an adult. It migrates regularly, probably to look for fresh breeding sites.

Hoverfly Volucella bombylans, photo by Rob KnellVolucella

Volucella are a genus of hoverflies that lay their eggs in bumblebee and wasp nests.

Volucella bombylans is a large hairy fly. It is about one half of an inch long and has a wingspan of approximately one and a half inches.

There are two varieties of Volucella bombylans. One looks like a yellow-banded bumblebee, with hairy yellow bands. The other is black and has a red tail - it resembles the red-tailed bumblebee, Bombus lapidarius.

Volucella bombylans lays its eggs in bumblebee nests. When the eggs are hatched, the larvae scavenge the nest, eating dead bees and dead larvae.

Other species lay their eggs in wasp nests.

These are less hairy than Volucella bombylans.

Hoverfly Volucella pellucens, photo by Christiane SvaneAdult Volucella pellucens lay their eggs on the paper envelopes of wasp nests.

Most of the larvae fall to the midden below the nest, where they eat dead wasps and larvae.

Some are able to squeeze into the paper cells with the wasp larvae. They live off the wasp larvae's secretions.

Eventually, all of the larvae penetrate the nest completely. There they eat living wasp larvae and pupae.

Volucella larvae become fully grown in the autumn. They hibernate until May or June, when they become pupae. In July or August, they emerge as adult flies.

Hoverfly Microdon analis, photo by James LindseyMicrodon

Hoverflies of the genus Microdon look like honeybees.

They lay their eggs in tree stumps that contain ant nests.

After 12 days, the Microdon eggs hatch. The larvae feed on discarded food pellets that the ants eject from their mouths. The ants appear to ignore the larvae.

When the larvae are fully grown, they remain in the drier parts of the nest until April or May, when they change into pupae.