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

Records from photographs - a conundrum

At the start of this week I hit a brick wall in terms of the effort I make to extract data from websites. It is a pretty huge task these days, but when I started six years ago it was in its infancy. The growth in photographic recording has been massive and these days I am unable to keep on top of it without working a minimum of 50 hours a week. That is unsustainable as I find it getting in the way of my ability to earn a living! So I posted on various forums that I was going to cut my commitment at Christmas and would restrict my involvement to one or two forums.

I was looking to see what expressions of interest there might be to help out. The result has been very helpful, with an excellent software engineer volunteering to build a data extraction bot and website (he has one up and beta-testing already!). Two other people have offered help. On the whole, comments have been very positive but I did get one response that raised all the questions that are raised by taxonomic specialists – what is the value to be had from ad-hoc photographic records?

This is a really important question and one that deserves careful analysis because in my view the national datasets are increasingly skewed towards such data. Certainly that is the case for hoverflies and I suspect that a similar situation will obtain elsewhere. Does it matter? And, if it does not matter, what are the benefits of growing a bigger network of recorders who perhaps only record part of the fauna?

At one time I might have held similar views to those expressed above, but I have given a lot of thought to the issue and have concluded that on the whole the benefits vastly outweigh the drawbacks. My reasoning is as follows:

One can either take a highly insular approach to recording and confine recording schemes to the outputs of a very small number of recorders who cover all taxa within a particular family. Alternatively, one can absorb all records and recognise that the dataset will be disproportionately skewed towards those species that people see and can identify without resorting to taking a specimen and undergoing microscopic examination. The two approaches yield very different data profiles, and in the past the outputs of key recorders would have dominated the dataset (for about 30 years the dataset was dominated by just 20 very active recorders. Many of those recorders are no longer very active and the datset is now growing from a new cohort of recorders, rather fewer of whom cover all taxa. Thus, the HRS dataset now fits much closer to the dataset emerging from photos. All the same, provided one has a clear picture of who records in particular ways one can split the data according to technique and analyse it accordingly. So there is no real problem from a data management perspective.

There then comes the issue of rarity or difficulty of ID. Whilst the occasional record of a 'rarity' might be of some interest, it is of limited value when wanting to analyse trends – you need an awful lot of records to do much trend analysis, and by its very nature rarity precludes such analysis. In actual fact one does find from some photographs that there are more of certain species than we might think – e.g. Palloptera muleibris turns up far more frequently as photos than it does in my net (I think I've seen it twice in 30 years!). The data for many hovers and larger brachycera have contributed to the various species status reviews. So, if we judge datasets on rarity then maybe they are not covering all taxa, but in actual fact photographers do see species that the specialists rarely see – for example I reckon that there are more photographic records of Actophila superbiens this year than will come from specialists.

I would then suggest that 'common' species are often the bellweather of changes in the wider countryside, so big datasets of species that people can identify may actually tell us quite a lot about the natural world. We can do this with a variety of hoverflies from photos – changes in emergence periods and in distribution. The data are too limited yet to look at trends but they are improving.

Finally, I think we must look at what one is trying to do when engaging with photographic recorders. We have to be realistic that this is the biggest cohort of natural historians and is increasing in influence. We either engage and hope to show how there remains a need for sound recording by collection, or we shrink into a box and fight people off when attacked. I favour the former and that is why I put effort in. What is more, if the biological recording community is to remain active and relevant, the photographic community is a very big constituency so we need to engage and to show what can and cannot be done with data accumulated this way.

So, am I wasting my time? Well if some people think that is the case then they don't have to get involved. But, we rely on a very small band of people to make the detailed datasets and those alone will not provide some of the data that are important. If by outreach we pick up the occasional person that gets more deeply involved, or converts to using a microscope (there have been a few), then there is a future for sound taxonomic recording. If we fail to do that outreach and to show value to what people are doing, not only will recording diminish as the current generation pops its cloggs, capacity to generate new competency will also diminish. If I was a politician reading some comments I would be thinking – why bother with this lot – they are not inclusive and are negative. If I got too positive a message I might develop too many expectations.

My view and approach is to look for a level of input that demonstrates both the value and the limitations, but the main limitation is the lack of specialist capacity. I have previously written about the need to develop more expert capacity, and I believe that developing the recording effort via engagement with photographers is a valid way of doing so. It may not be 'ideal' but then if you wait for the ideal situation it is unlikely to happen.

It is also worth bearing in mind that the sort of engagement I have made means that large numbers of people have developed an interest in diptera at some level. Some will buy the books - e.g. the revised Larger Brachycera book. We need to drum up interest in order to sell enough books to make them economically viable. If we don't then such books will not get published. Increasing interest helps to sell the Wildguide and that in turn generates an income to produce guides such as the hoped for Scathophagid book (we have donated the proceeds to Dipterists Forum). Likewise, that interest may help to generate the case for a Diptera Wildguide - and for that my database may be essential to source relevant photos. So, it is not a simple question of limited records, there is a strategic case too.

There is a genuine need for debate about the value of different recording techniques, but the most important issue is to think about what positive benefits can be accrued. If we don't make an effort to extract data and to engage to encourage, then we are missing a time-limited opportunity, as the people who can provide the taxonomic expertise are aging and we need to grow a new constituency of specialists to provide the detailed taxonomic advice.

Is something happening with Rhingia campestris this year?

Rhingia campestris is a common, readily identifiable species that is reported by specialists and generalists alike. It attracts a fair amount of attention from photographers and figures within the 20 hoverfly species most frequently recorded by photographers. It is also known to be very responsive to the effects of drought – a feature that Stuart and I drew attention to in a presentation to one of the hoverfly symposia several years ago. This relationship had previously been highlighted (but not recognised) by reports of its abundance dating back to 1947. In really hot years, the second generation is largely absent. This can be seen from past records, but sadly we generally get insufficient records to do a great deal with the data.

In 2014 R. campestris was frequently reported in April and May, and it is clear from the data that this is one of a suite of species that definitely respond to warm springs. What has happened since is more puzzling. The numbers of records have tailed off but have not dropped to a clear separation between generations. Perhaps this is the effect of northern generations emerging a little later? I must look at the data in more detail to see if this is the case, but what is clear is that the overall shape of the graph for the year to date (using a five week running mean) is somewhat different to the previous three years for which sufficient photograpic records exist.

What is also very clear is that 2013, where there was a very hard winter and later spring exhibited a clear twin-peaked phenology that is less evident in other years. The data may not be robust enough to make too much of this observation, but I do wonder if a study of bivoltine species might show how such species change their emergence patterns in response to longer breeding opportunities.

This brief observation illustrates how it may be possible to generate useful and relevant information on the effects of changing climates on our wildlife. It shows that 'common' species are highly relevant to the understanding of the natural world and should encourage more recording of such species. The big question is 'how to deal with the volume of data that could be generated by a serious initiative to record common insects?' Maybe there is scope to develop ideas by MSc students?

Yearly phenology for Rhingia campestris using photographic data using a five week running mean