Tuesday, 3 January 2017

Hoverfly identification: getting started with the WILDGuide

When I was young and got a new identification guide (in my day the Wayside and Woodland series and the Observer's books) I would avidly read the entire contents and would then seek out the animals I was particularly interested in. I well-remember making my first discovery of Puss Moth eggs when I was nine or ten years old - just as the book said, laid in pairs on the underside of poplar leaves! I have always assumed that other field naturalists did much the same, but I suspect not. My suspicions were reinforced a year or so ago, when after a lecture in London, one of the questions that came from the floor was (slightly paraphrased):

'I have the WILDGuide and it is rubbish; can you suggest a book that can actually get me to species - one with keys'?

My reaction was that the WILDGuide did contain keys and that the questioner should 'read the b....y book'! It got me thinking, however: we went to a lot of trouble to try to design a key to get readers to the Tribes, but do they use it? I guess some will and some will not. The important point is that the guide was not designed like the classic bird guide with plates of pictures that you simply match to the bird you have seen. I say 'simply', but from experience making a diagnosis of birds is far from easy without a respectable knowledge of the critical features and what to look for. The same holds for hoverflies and, indeed, most animals and plants. If you simply start at the beginning of the pictures and try to make a match, it is possible to go wildly wrong!

So, where should one start?

The obvious place is 'at the beginning'. Arriving at a firm identification for any group of organisms depends upon one's knowledge of their anatomy and morphology. The anatomical elements can be learned from text books, but it does have to be applied. There are subtle differences in the way anatomical features are expressed in different animals, even within the same family, so it take a bit of time. Which is where comparative anatomy and morphology come into the equation. Taxonomists rely on comparative anatomy to make their diagnoses and tend to rely on interpretations of anatomical evolution to ensure that they are describing the same feature in a range of animals. In flies that is horribly complicated because the evolution of the wing veins is complex and somewhat uncertain in places (try working out the original origins of the veins in the Phoridae for example!).

When we run training courses, we put a lot of emphasis on making sure that the group understands critical anatomical features. If you don't understand these, the keys are a nightmare. Similarly, if you don't understand what separates the Syrphini from the Bacchini, or the Cheilosini from the Chrysogastrini, life can be pretty complicated. So, if you don't have a chance to go on a course, you can teach yourself to some extent and that will make life a lot easier. Some features (many) are microscopic, and thus it is a lot easier learning from microscope and specimens, but modern photography is remarkable and it is amazing what can be done from a good set of photos. So, for those just starting out this winter, I suggest bringing up photos from the Facebook Group and seeing if you can run them through the key to Tribes.

It is all about markers

Using a key gets easier with time. Once you know how to find a character, it is a whole lot easier to establish its form. Does it have eye hairs, is it peculiarly shaped or is it a particular colour pattern? But, beware, there is always the exception that causes a major headache. The Hoverfly WILDGuide  is a half-way house because it was intended as an introductory guide that compliments the more comprehensive monographs. Although there are keys, it is true that the book is not based on keys. I often find it useful to go back to Stubbs & Falk and actially verbally run through the sequence of characters to help FB members find their way around difficult genera. That said, one has to be careful not to do this too much otherwise sales of the main monograph may be compromised.

In hoverflies, the biggest problems I think are:

  • Teneral specimens in which the colours are not fully formed;
  • Inaccessibility of some critical features such as elements within the genital capsule;
  • Specimens that develop under exceptionally warm or cold conditions, whose patterns are greatly affected by temperature;
  • Species with spring and summer broods and exhibit brood dimorphism; and
  • Misinterpretation of dusting because of glare or rubbing.

All of these factors combine to make life difficult, so there is no real substitute for experience. The more you see, the more likely you are to have seen some of the problems and know what they mean. There is no rule that says every specimen can be taken to species. Even the most experienced taxonomist will have a small selection of specimens that they are unsure about. As time goes by I find myself getting increasingly uncertain about some genera! If in doubt, put it to one side and try again later, or seek an opinion from a recognised specialist. Beware, there are people who will give a diagnosis based on spurious characters. It is best to stick with reliable techniques because taxonomists don't deliberately set out to make things complicated;  things get complicated as more and more specimens emerge that don't fit the conceptual model of the characters that define the species.

Nevertheless, as time goes by, you will start to know the critical markers. For example, one of the most useful ones is the loop in vein R4+5 that defines the Eristalini and the genus Merodon. Episyrphus balteatus should become familiar quite rapidly (but dark and pale forms may still confuse). Fortunately, if you start recording in the early spring, you will be eased into the bewildering array of forms and will hopefully acquire markers from those early species.

It does not happen with the click of a finger!

When I started working on hoverflies I spent innumerable evenings poring over specimens under the microscope, muttering 'these are impossible'. Of course they were not impossible, and I have overcome the worst of the early challenges. I think it takes about 3 years to acquire a reasonable grounding in hoverfly identification, at which point you realise that there are innumerable species that you have not seen. At that point, it is time to go back to the texts and learn about the ecology of species that you have not found. In this way, you should get to see more species because you know what to look for and where to look.

1 comment:

  1. Another great post Roger. Great for numpties like myself.