Take nothing but photographs?

The issue of retaining specimens is one that will never go away. Some believe that one should take nothing but photographs and leave nothing but footprints. This mantra has existed for a couple of decades, and has become very firmly embedded. Others, perhaps an 'old school', are more relaxed about retaining specimens of invertebrates; and then there are the specialist taxonomists whose experience points to a continuing need for retaining specimens. Who is right? Or, is there a 'right' and wrong' answer?

BWARS have produced their own policy on specimen retention and rightly point to the need for restraint. They also highlight the dilemma that faces the serious specialist – your subject area is fascinating, and the animals are delightful, so why kill them? In my case, I gave up moths many years ago because I no longer felt that I could justify specimen retention on the grounds that I was not adding much to science and that my collection would not be wanted by a museum. Moreover, I was confident at the time, that with a small number of critical exceptions I could cope with live specimens. Thirty years on, I find I have forgotten everything about moths and they cause me a headache! I've not got the time and energy to go back through the learning process again!

Do we need to retain specimens at all - Where is the evidence?

The view that photography alone will suffice is reinforced because people can now take a photograph and post it on one of the specialist Facebook groups or iSpot. In many cases they will get a name, either complete or partial. Whether the determination is correct is another matter! Unfortunately, there is very little in the peer-reviewed literature that quantifies the issues. I have tried to provide some basic statististics but my patheitic attempts were met with reviewer comments ranging from 'of little scientific importance' to 'grossly misleading and wrong'. One reviewer ranted that at best 10% of hoverflies could be reliably identified from photographs. I gave up trying to produce something to fill one of the gaps!

Yet, I have good data from nearly ten years of extracting records from photographs. Those data now comprise perhaps as many as 100,000 records (approximately 10% of what has been assembled by the Hoverfly Recording Scheme over 40 years). I also have a good run of personal records that have been collected consistently over 30 years (maybe 40,000 records). So some comparison can be made. Similarly, there are now several recorders who are primarily photographers, but who also retain specimens that they send to me for determination. These three models can be compared, although scientific purists would argue that one really needs to compare photographic data with data derived from a rigid trapping protocol.

Are hoverflies a useful model for evaluating the potential of photographic recording?

Hoverflies are one of those 'in-between' groups. Some are relatively straightforward to identify from photographs, providing the photograph is of sufficient resolution to evaluate form and markings. Even so, we occasionally see photographs of relatively straightforward species that cannot be firmly identified. A far greater proportion can be identified on occasions, but unless critical features are well depicted we will struggle to get any further than generic level. There are then the genera that cannot be identified from photographs at all. For example, many male Platycheirus are determined on the basis of pits on the undersides of their feet – those are not depictable in live animal photographs. Some species can only be done from the internal structures within the male genital capsule (e.g. Sphaerophoria). Others are simply fiendishly difficult without access to comparative material (and even then cause problems).

We must also remember that we have a typical 'island fauna' that is a sub-set of a bigger continental fauna. Our 284 species of hoverfly compares with over 800 species in Europe. The fauna's of our near-neighbours in The Netherlands and Belgium are perhaps 20% bigger, even though their land area is much smaller. It makes our job easier, but we also forget that we may well be overlooking cryptic species amongst species that we currently believe to be one 'easily identifiable' species. Eristalis is one potential problem area.

What do the data tell us?

A post on this blog earlier this month provides some indication of the sorts of differences that can be seen when photographic data are compared with data collected by a specialist. The most significant differences was in the relative importance of Cheilosia in the specialist dataset and the much higher representation of Pipizella and Paragus in that dataset.

The overall message is that photography can, and does, generate a large number of valuable records. Photographic recorders also ensure much wider geographical coverage, and will find species that occur at very low densities that are not well represented in the specialist dataset. The data are, however, a sub-set of the overall fauna. 

Does it matter

If you are a naturalist who simply wants to know roughly what the animal or plant you have seen is, then the quality of identification is not a huge issue. It might mean that the 'lister' achieves longer or shorter lists depending upon the level of caution used in coming to a determination.

The issues start when data are used for other purposes such as site safeguard and development of species conservation strategies. If data are skewed then it is easy for developers to undermine the confidence that can be placed on individual records and on the conservation status of species. This has always been a problem for invertebrates and they are still very much a Cinderella area. To the best of my knowledge there remain no SSSI based solely on invertebrates; yet there probably should be. In the days of NCC and English Nature it was an uphill battle to get invertebrates the recognition they deserved. When BAP was developed, a huge list of birds went on as priority species, yet invertebrates that had undergone similar levels of decline were rejected because the data were believed not to be reliable.

Thus, the message has to be, if you want to see invertebrates properly conserved, you need robust data. We just about manage this for hoverflies, but getting similar levels of coverage and detail for, say, fungus gnats or craneflies is impossible. Why? Because they rely on high magnification and often upon characters that cannot be seen in photographs. Perhaps more importantly, because there are a handful of specialists capable of identifying them and those specialists (wisely) will not spend their lives glued to a computer screen identifying photographs. And, finally, not all insects are large and charismatuic. Many are minute and difficult to find.The generalist photographer will not find them and even the competent specialist may miss them unless they take a large sample. Those species make up a significant part of our fauna but will not get the recognition they deserve unless they are properly recorded.