Episyrphus balteatus (De Geer) |
Order: Diptera – true flies
British distribution: Throughout Britain.
World distribution: Europe, Asia.
|Episyrphus balteatus on Small Scabious, Scabiosa columbaria, Blows Downs, Bedfordshire, July 2004.|
Like most other hoverflies, Episyrphus balteatus is a Batesian mimic – harmless but closely resembling a dangerous or distasteful model – in this case having the appearance of a solitary wasp.
It is just one of a large number of hoverflies (family Syrphidae) with narrow bodies, and with abdomens barred with black and yellow – though in this case the yellow tends towards orange. Many of these are in the tribe Syrphini ('tribe' is a sometimes-used classificatory rank between genus and family) and at one time were in the genus Syrphus, though this genus is now split up into a number of separate genera. They are a difficult group, but E. balteatus stands out by having secondary black bands on the 3rd and 4th tergites (dorsal plates) of the abdomen. The posterior margins of these tergites are heavily banded with black, but towards the anterior margins are the smaller, often broken bands, that in shape remind this author of a stick-on false moustache! The development of these bands is, however, variable.
A further identification character is provided by the faint, grey, dorsal stripes running longitudinally on the thorax – not always conspicuous but easily seen on the photographed individual.
The diagnostic anterior bands on the abdomen of E. balteatus. Also visible here are the halteres, balancing organs, that replace the hind wings and are diagnostic of the Diptera. They are yellow in this species.
E. balteatus is one of our most common and widespread hoverflies throughout Britain, throughout most of the year and in a variety of habitats including urban gardens (though the photographs shown here are from chalk downland). It visits a variety of flowers for nectar, but seems to have a particular prediliction for dandelions (Taraxacum species).
In some years its numbers are supplemented by migration from the continent, occasionally in such numbers as to cause consternation to those taken in by its resemblance to a wasp. Panic amongst holidaymakers on the Essex coast in the face of such a mass immigration was reported by the Guardian, Tuesday August 3, 2004,
The larva is terrestrial, a voracious consumer of aphids. Considering too the rôle of the adult fly as a pollinator, this makes E. balteatus an entirely beneficial insect, despite its wasp-like appearance.
|The excellent and definitive account of British hoverflies is:|
|• ||Stubbs, A.E., & Falk, S.J. (2002). British hoverflies. An illustrated identification guide, ed. 2, British Entomological and Natural History Society, Reading.|
|A comprehensively detailed description (as Syrphus balteatus) is given in:|
|• ||Verrall, G.H. (1901). British flies, vol. 8: Platypezidae, Pipunculidae and Syrphidae of Great Britain, reprint, 1969, E.W.Classey, Hampton.|