Saturday, 22 September 2012

WILDGuide: Britain's Hoverflies

Some readers will be aware that Stuart Ball and I have been writing a new book on hoverflies in the 'Britain's' series published by WILDGuides. It has been a much more challenging venture than we had originally anticipated and we are still adding the finishing touches. We have seen page proofs and they look very good. It will be worth the wait and for those lucky few who have pre-ordered via Dipterists Forum it will come at a bargain price. Since we advertised the deal the RRP of the book has risen substantially. We hope that the book will go to the printers in the next month or so, and therefore it should be on the bookshelves before the spring.

Our intention is that this book will be a companion to Stubbs and Falk. It will hopefully help the novice get to grips with the family without the very difficult elements of the opening 'Key to Tribes' that causes so many problems. Over 160 species will be illustrated and we spent many months photographing specific characters that should make identification of some tricky species easier. However, it is no substitute for the comprehensive monograph and anybody wishing to make accurate identifications of trickier species will still need Stubbs and Falk as well as access to a microscope and voucher specimens.

Hoverflies are not easy to identify, and many species can really only be identified under high magnification and by referring to comparative material. We think that perhaps 100 species can be done from photographs or in the field if you are very experienced. I personally reckon to recognise down to species pairs for maybe 200 of the 281 species. But, this is after 30 years of experience and having spent many months poring over difficult specimens. Anybody who has attended our training classes will tell you that even now there are specimens that cause me difficulty. So, the key message for the novice is to keep at it as they do get easier.

We have been extremely clear that this WILDGuide cannot be expected to be comprehensive. Indeed, we have resisted incorporating a broader selection of species and  additional notes on identification of species that have not been illustrated. We have done this for a variety of reasons, but mainly because we think it is important not to suggest that hoverflies can be identified on the basis of a limited description of differences from illustrated species.

Some readers may view this as a mistake but we now have a great deal of experience of the problems that can be encountered. What is more, we too hit problems when using detailed keys and even when we have access to comparative material! So, we think it is best to minimise the opportunities for avoidable mis-identifications.

Our hope is that the WILDGuide will act as a stimulus to interest in hoverflies and that this will lead to a greater use of Stubbs and Falk in due course. We have a revision of this monograph planned for the next five years and will be producing an interim supplement this winter. There are plenty of jobs to get on with and we won't be short of things to do!

Checking that identifications are correct

It is remarkable how often recorders make simple errors in identification. There are numerous permutations and new ones emerge on a regular basis. The commonest mistakes include:
  • Naming females of species that can only be be identified reliably in males.
  • Naming species that can only be identified using microscopic eye hairs or wing hairs that are not visible on photographs.
  • Naming species that clearly do not occur in the area they are recording from - the most obvious mistake being to report coastal species from inland locations and to report northern species from southern locations.
We have developed our introductory guide with these mistakes in mind and have attempted to minimise the potential for new mistakes.  However, doubtless more will emerge and we will eventually have to revise the book in the light of problem identifications. Perhaps the commonest misconception is that each hoverfly is very different from all others. Unfortunately this is not so and there are numerous problem genera: Cheilosia, Eupeodes, Heringia, Pipiza and Platycheirus,to name but a few.

Mistaken identifications can be tricky to spot when one is presented with a simple list, but if a knowledge of the biology of the species and a good feeling for British geography and the distribution of habitats makes it easier spot the problems. Records of certain species are especially telling. For example we frequently get records of Platycheirus immarginatus from inland locations, yet when we map reliable records of males (which are more straightforward) it is clear that this is a strictly coastal species. There is a moral to this story: making a correct identification depends upon use of keys, illustrations and species descriptions. The species descriptions and accounts of geographical range in Stubbs and Falk are especially useful as they highlight additional characters and describe the ecology as best we are able to say.

When lists of species arrive at the Recording Scheme, I immediately look to see what is listed and the relative proportions of difficult and more straightforward species. No list is wholly discounted but if I am uncertain of the reliability I will mark them as uncertain. These records do not appear on maps or in analyses.

Seeking help

I am always happy to help with problem specimens and will do my best to put a name to photographs. However, there will be times when a certain identification is not possible.  Occasionally specimens have to be passed on to other specialists and now and then they have to go to a European specialist for an opinion.

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