Volucella bombylans is a consummate bumblebee mimic, and even has two colour forms. Volucella bombylans var. plumata (left image) has a white tail, mimicking the white-tailed bumblebee Bombus lucorum and the buff-tailed bumblebee Bombus terrestris. Volucella bombylans var. bombylans (centre image) has an orange-red tail, mimicking the red-tailed bumblebee Bombus lapidarius. The right image is the hornet-mimic hoverfly Volucella zonaria.
Hoverflies lay their eggs during spring-summer. These hatch and the larvae feed on their particular food materials as indicated above. When fully fed, the larvae pupate, with those living as larvae in wet situations often moving to dryer places before pupating. Most hoverflies have one generation a year but some have two. Hoverflies overwinter as larvae, pupae or in some species as adults.
Role of hoverflies in gardens
Hoverflies are generally beneficial insects as many have larvae that help to reduce aphid numbers, others help recycle decomposing organic matter. Flower visiting by the adult flies means that hoverflies are also useful as pollinating insects. The Syrphidae does have two species that damage garden plants, narcissus and house leeks, but then most families have at least one reprobate.
Encouraging hoverflies in gardens
Adult hoverflies visit flowers to feed on pollen and nectar. Most species have short mouthparts, so they use flowers where pollen and nectar is easily accessible, such as flowers of the daisy type. They also feed on the sugary honeydew excreted by aphids. Judith Webb's paper listed below is an excellent source of information'
As with other pollinators, avoid double flowers. You need flowers that open in hoverfly flight periods, which are generally May, then again from late July to early autumn. They prefer open flat flower heads to land on, preferably with many flowers, such as the Apiaceae
(previously called umbellifers) which includes hogweed, fennel, cow parsely and ground elder. Other good plants are species of Eupatorium
(including hemp agrimony Eupatorium cannabinum
), oxeye daisy Leucanthemum
spp, and buttercups Ranunculus
Among shrubs, privet and elder are excellent, and the spindles Euonymus
spp. The best trees, are lime Tilia
spp. and sycamore Acer pseudoplatanus
which are good because of the honeydew
they produce. The best climber, as for so many other garden creatures, is ivy Hedera
Finally it's worth noting that for pollen feeding, some wind pollinated plants such as grasses, hazel and oak offer very rich pickings for hoverflies.
Other sources of information
Judith Webb's paper
"Flowers for flies"
Ball, S. & Morris, R. (2015) Britain's Hoverflies: A Field Guide, Revised and Updated Second Edition. WILDGuides
Stubbs, A. & Falk, S. J. (2002) British hoverflies. British Entomological and Natural History Society
Page text drafted by Andrew Halstead, reviewed by Andrew Salisbury, compiled by Steve Head