Source: Entomologist’s Monthly Magazine 157: 258–260, doi: 10.31184/M00138908.1574.4105 © Pemberley Books

BOOK REVIEW (hier als .pdf)

BLOW FLIES (DIPTERA: CALLIPHORIDAE, POLLENIIDAE, RHINIIDAE), Handbook for the Identification of British Insects Vol. 10. Part 16 by Olga Sivell. Paperback, 2021, 206 pp. Published by the Royal Entomological Society. ISBN 9781910159064. Price: £39.95

As a PhD student at the Institute for Legal Medicine in Cologne, my only source for forensic fly determination was Smith’s Manual of Forensic Entomology (1986). I had bought the last copy of this book ever sold by the Museum of Natural History in London.. The shop staff there considered the book to be rather an oddity. When I later met its author Ken Smith (1), who had never left England in his life (or so he told me), he mentioned that his book was considered to be ‘historical’ and needed a thorough updating. Disappointingly, the museum declined the updates to Ken’s book that I subsequently offered. Accurate species determination is essential for forensic entomologists. Of course, DNA barcoding, which some now consider to have superseded traditional methods of taxonomic determination was in its infancy when Ken was writing. And today, traditional morphological studies still have a very significant role to play in forensic entomology. In fact, molecular determination methods may not be as reliable as some think and at times should be distrusted because of misidentifications in databases.

So in the absence of an update to Ken’s book, we switched to self-made keys, containing more and more photographs and morphological definitions. This was becoming increasingly important because our students were beginning to join us knowing less and less about insect morphology in general, not to mention such detailed morphology niceties as hypopleural bristles or coxopleural streaks, for example! A former trainee, now professor at Toruń University, Krzysztof Szpila, also developed keys and took (and still takes) excellent light and REM photos. But we have found that REM pictures are often too detailed or unusual for students to interpret, as are the numerous and fine drawings in Rognes’ key from 1991 (Blowflies of Denmark and Fennoscandia). A quick key developed by Szpila in 2009 (Key for the identification of third instars of European Blowflies of forensic importance) pioneered the use of high quality light photographs. Such improvements went on for two decades but all updates, initially printed on colour laser systems, were then expensive and time-consuming to produce.

Finally and to our relief, we now have this magnificent new key from Olga Sivell, which out shadows everything that we have previously had available for the identification of adult blow flies (Calliphoridae, Polleniidae and Rhiniidae). It is impeccably bound and printed on coated paper. It has a fresh, modern style. Drawings are only included where they are truly necessary. This helps with the modern look as line drawings may seem old-fashioned to the current generation of entomologists. I would like to stress how the superb mixture of clear drawings and photographs makes this key very user friendly.

As an additional eye-catcher, Sivell includes a stunning photographic introduction for each subfamily, accompanied by well-written articles about the species, including synonyms and reference to relevant literature. I also appreciate the look-alike section. Lucilia does have a few mimics amongst the muscids and tachinids – which our team already knew about. But we have been made more aware of other interesting mimics across families, such as the tachinid Esthera resembling Calliphora greenbottles – or the other way around? Inspired by the look-alike section, I asked myself which evolutionary and ecological mechanisms might be underpinning the morphological similarities shared by Eurychaeta palpalis (Calliphoridae) and British sarcophagids. How? When? Why? Maybe Olga Sivell’s key will inspire some spin-off research here.

To test the merits of the new key, my team and I chose grubby and worn flies from our true crime case collection. The specimens had already been reliably determined morphologically by two independent experts. First, we checked Lucilia sericata because it is so very commonly found on corpses. It immediately impressed us that all the photos in this key are beautifully taken and arranged. For example, the explanatory images given for the basicosta as well as the hair on the lower calypters are particularly helpful. The basicosta is sometimes variable: carrying a black shield that is not accounted for by the ‘pale’ look asked for in the key. In the case of the hair on the calypters, the photos are useful as these hairs can be short and pale, and easily overlooked.

We can almost set the clock on when the first questions relating to these features will be made by students during our determination classes – so Sivell’s images are particularly welcomed. There are, however, examples of where additional photographs would have been useful. For example, the inclusion of a photograph of the pairs of postsutural acrostichal bristles referred to on p. 57 would be very helpful, or perhaps a reference to p. 22 where a nice drawing is already given.

My laboratory team often tells me that our students have not been exposed to sufficient basis insect morphology before embarking on the detailed determination required of forensic entomologists. Sivell’s key will go a long way towards mitigation against this deficiency. Overall, determination of Lucilia adults is a pleasure with this key because the exact location of the relevant hairs on the occiput is clearly illustrated, and the genitalia are portrayed as photographs and drawings. An arrow pointing to the coxopleural streak, the ultimate arch-enemy of our students would be most helpful in couplet 6.

To look a little more into details, we proceeded to test the key with further species. We found the mention of the subscutellum helpful – its presence leads straight to tachinids and makes it impossible to turn in the wrong direction at this point of determination. Reference to subscutellum and tachinids is generally missing in Smith (1986) and Greenberg & Kunich (2002, Entomology and the law: Flies as forensic indicators. Cambridge); and Erzinçlioğlu (1996, Blowflies, Naturalists’ Handbook 23) mentions that the structure is missing in blowflies yet does not say in which family to expect its presence.

We do not see many tachnids in our cases but the inclusion of the subscutellum is a valuable safeguard – ‘it is, of course, a trifle, but there is nothing so important as trifles’ (Conan Doyle, The Adventures of Sherlock Holmes). Another trifle, the flattened mesonotum feature leading to Protophormia terranovae in the key of Juan Marilius in Greenberg & Kunich to distinguish P. terranovae from Chochliomyia and Chrysomya is missing in Sivell’s key. She does, however, highlight the importance of first looking for strong bristles in the lower parafacialia region to separate Eurychaeta palpalis from Sarcophaga spp. This protects the students against hasty and misleading travel into the world of flesh flies or the ‘non-forensic’ Helioboscinae.

Pollenia rudis was our next target. The drawings accompanying the steps of the key are nicely done, particularly those of the scutellar margin as well as the inner posthumeral bristles. Here, it would have been good to cross-reference the useful, coloured drawing on p. 70 to assist recognition of the facial carina. Also, since the presence or absence of this feature is prominently used in the key, it would be helpful to know if the feature ‘no facial carina’ exists or if there are just narrow or wide ones – maybe an idea for a further figure?

Finally, determination of Cynomya is a straightforward matter with this key. It would be a friendly gesture to include a link to the figure of the bristles on p. 22 since acrostichal bristles can be a pain for students as a result of inadvertent vertical pinning through this area of the fly thorax. I usually prefer to work on insects under methylated spirits to keep them flexible (and with the pin out,) but Sivell’s key might now make me switch to dried specimens – many of the features in her key were more easily recognizable dry and with the fly fixed on a rotating mount.

Species like Cochliomyia macellaria are not mentioned in the key, which is good on the one hand as it helps avoid confusion between old and new world species. On the other hand, their mention might be a service to students in the section where the key points towards Chrysomyinae. In my lab at least, these flies are of relevance since I work internationally, and my insect-digging box for beginners does contain them.

Similarly, Afrotropical, Neotropical or Oriental Chrysomyia flies cannot be determined to species level with Sivell’s key (it just leads to subfamily level: Chrysomyinae). Anyway, trying to determine a specimen of these flies gets us stuck on top of p. 55; the cream-coloured calypters with darkish hair on the upper calypter constitutes an impossible mixture of features in this key. All such extra hints would of course just be nice-to-have, and they are far from necessity.

My team and I have been involved in the morphological determination of forensic flies for decades now, often assisted by inexperienced students, and after our test runs on Olga Sivell’s new key, we uniformly agreed that we love it. Never again will the words ‘well, this feature is hardly recognizable’ be spoken.

MARK BENECKE

(1) K.G.V Smith was Editor-in-Chief for the Entomologist’s Monthly Magazine 1981–2010.

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