Identifying hoverflies from photographs

Identifying hoverflies from photographs is not straightforward. Photographs depict a single plane and do not allow rotation to look at particular characters. By comparison, preserved specimens can be viewed from many angles under the microscope. In addition, most keys have been developed from preserved specimens, which can differ markedly from live animals. The art of identification from photographs is therefore in its infancy. As photographic techniques improve, identification techniques may also improve; but there will always be some hoverflies that cannot be identified at all from photographs. That said, it is realistic to assume that around 50% of the British fauna can be identified from at least some photographs. There are a number of obvious ways in which photographers can be more assured of a positive identification:

• The higher the resolution of the photo, the more chance of actually seeing key characters. For example, really nice sharp and well-filled frames can expose hairs on eyes, leg hairs and occasionally the pilosity of the arista.

• Views from several angles top, front face and side view often combine to provide enough information to give a positive ID.

• It is worth developing a knowledge of the family so that you have a rough understanding of the genus you are photographing. Each genus depends upon a slightly different range of characters and once you have a feel for the genus it should be easier to make sure that key characters are depicted.

There are some genera that cause particular problems - the most frequently illustrated genera that don't get identified are within Cheilosia, Eristalis, Platycheirus and Syrphus. That is not to say that they are the most difficult to ID in other circumstances, but they are the most frequently depicted genera from awkward angles. In addition, there are some tribes and families that are most unlikely to get identified because they rely on characters that are difficult to show in photographs. These include the Platycheirus where pits on the underside of male tarsi can never be seen in live specimens, and Eumerus, Pipizella and Sphaerophoria where it is not possible to examine the male genitalia. The tribe Pipizini is altogether difficult, even under the microscope and is unlikely ever to be readily identified from photographs; so too are many Cheilosia.

But, if one ignores the problems (a good idea) IDs can probably be given in 60% of cases to around 150 species. The others fall into the too difficult group or will only be ID's from an exceptional photo.

The following is a tabulation of the commonest ID problems that I encounter:

My ID (not necessarily right!)	ID posted
Eristalis intricarius	Criorhina berberina
	Volucella bombylans
Eristalis pertinax	Eristalis tenax
	Eristalis sp - various often not possible to go further
Eristalis tenax	Eristalis pertinax
	Eristalis sp - various often not possible to go further
Eristalis sp.	All sorts of views, often at angles that show few characters or are well out of focus.
	Eristalis rupium (quite regularly on iRecord)
Syrphus sp.	Epistrophe diaphana
	Eupeodes latifasciatus
	Megasyrphus annulipes - several on iRecord
	Syrphus ribesii - the chosen name for about 90% of posts, suggesting that little attention is paid to text in the main keys or that Chinnery is being used.
	Parasyrphus sp.
Eupeodes sp.	Xanthogramma pedissequum (agg)
Eupeodes corollae	Eupeodes luniger
	Eupeodes latifasciatus
	Parasyrphus punctulatus
Eupeodes luniger	Eupeodes corollae
Unidentifiable Eupeodes	Eupeodes luniger
	Eupeodes corollae
	Eupeodes latifasciatus
Leucozona lucorum	Volucella pellucens
	Cheilosia illiustrata
Merodon equestris	Volucella bombylans
Platycheirus albimanus	Platycheirus scutatus
Platycheirus scutatus (agg)	Platycheirus albimanus - a problem I think resulting from the WILDGuide that I hope we will rectify in edition 2.
Scaeva pyrastri	Eupeodes luniger
Volucella pellucens	Leucozona lucorum
Xanthogramma pedissequum (agg)	Eupeodes nitens - a Chinnery mistake