Saturday, 17 March 2018

Choice of pinning system - direct pinning or staged mounts?

Not all insects can be identified in the field or from photographs; indeed, the majority probably cannot. There are, however, a few specialists who can do a fair bit in the field and from photographs. They can only do so because they have spent many years studying preserved specimens. Most observers of the natural world probably will not want to delve that deeply into species identification, but they may be keen to get specialists to do the identification for them. So, we definitely need specialists who have taken the trouble to develop the requisite skills. Newcomers will only manage this by taking specimens and making the necessary microscopic studies to hone their skills. Some advice on how to prepare and preserve specimens is therefore a necessary part of the mentoring process.

So, you have decided that you need to retain specimens in order to develop your technical skills. How do you set about it? For this session I will concentrate on the choice of pins for specimens that have been killed using your chosen medium (freezing, ethyl acetate, crushed laurel leaves).

Let us start with the critical issue. The ‘collection’ is not there to be an adornment – it is a working tool and the specimens need to be prepared so that they can be examined carefully from all angles. Equally importantly, the specimen is of no real value unless it is accompanied by relevant data – who collected it, the date on which it was taken, the locality name and a grid reference (in the UK using standard OS grid is probably best recognised). So, the specimen needs to have at least one, and possibly several labels. Once you have put an identity to it you will need at least a second label. So you need space on the pin.

For most Hymenoptera and flies, there are two main ways of pinning. Traditionally, a long pin has been used directly through the specimen. There are two lengths of pin that have been used – ‘English’ pins that are 30mm long, and ‘Continental’ pins that are 38mm long. Museums tend to favour Continental length pins because they have more space on which to place labels. However, many ‘collectors’ of old would use ‘English’ pins because they take up less space, require shallower boxes and are cheaper (standard lacemaking pins). I much prefer the longer continental pins because they also allow a lot more space for handling specimens without damaging the specimen.

Directly pinning using Continental pins carries with it the problem of storing lots of specimens whilst they dry and before they are fully labelled, but it does mean that you only have to write your data labels and place these on the pin. Many (but not all) Hymenopterists use this system.

There is the alternative that many Dipterists favour: short ‘micro’ pins made of stainless steel and produced in a variety of lengths and thicknesses from AA (the finest and most expensive) to E. For the most part pins graded A1 to A3, B1 to B3 and C1 to C3 are likely to suffice for the vast majority of Hymenoptera and Diptera in northern Europe. I tend to use a mixture of A1, B1 and B2 for all of my work (I never need to pin the larger animals as these are often doable in the field or I don't attempt them (e.g. bumblebees - if I cannot do it in the field I would not take a specimen - so I don't record many bumblebees).

If you work with micro-pins you have the advantage that you can store large numbers of specimens in a relatively confined space. Dipterists tend to use ‘Crystal Boxes’ – clear plastic boxes with a plastozote lining. These boxes are relatively pest-proof, can easily be stored and are a good way to keep specimens before staging and labelling (see Figure 1).
Figure 1. Micro-pinned specimens in cyrystal box. These include occasional beetles too, although pinning is probably not the way any serious Coleopterist would work! (I simply find it convenient)
The problem with micro-pins is that you then need to create a stage for the specimen on a longer pin (ideally a continental length pin). This is a fiddly and time-consuming job! But, staging does bring the advantage that the ‘stage’ acts as a bit of a shock-absorber (Figure 2). There are no conventions to the size of stage that you should use, nor to label size, but it is worth bearing in mind that the bigger the label and stage, the more space that will be required to store specimens – and that can get expensive! The other thing to bear in mind is that you will probably want to investigate both the upper and lower sides of your specimen, so big wide stages may impede your view of critical features; which is why I opt for narrow 3mm x 3mm stages of about 1.5cm long.
Figure 2. Staged and labelled Sciomyzidae - note two types of Continental pins used here - the expensive ones with nylon heads and the cheaper steel-headed pins bought because devaluation of the Pound has pushed the Austerlitz pins out of my price range!
The next and most important question is how to prepare labels? If you have nice neat hand writing you can of course do so using a permanent marker pen or Rotring pen. My eyesight and hand writing are too poor for this and I don’t have the time to write vast numbers of labels; so I generate them on the computer and print them onto thin card (ideally acid-free). Don’t use ink-jet printer unless you get permanent museum-grade ink. Other inks will fade and become illegible. A laser-printer is far more reliable and produces cleaner labels. I tend to go for labels in 6 point and using 0.7-line spaces. In so doing I can usually create labels approximately 1.5 cm by 1 cm. Remember that the labels need to be legible (at least under magnification) and they need to last if the specimen is to be of any long-term use.

Finally, it is important to remember that a 'collection' need not be a work of art! I tend te refer to specimens as 'a bit of chitin on a pin'. The real value of the collection is the science, so the specimens need to be accessible but not beautiful. I tend to side-pin pretty nearly everything with flies and have now started to side-pin some aculeates too (e.g. Pompilidae). Carefully spreading the wings may have no real value but may be aesthetically pleasing. But, it is important to be able to see relevant venation, so making sure critical features are exposed is essential. This can mean teasing out male genital capsules, ovipositors and possibly opening mouthparts (some bees). It is fiddly and time-consuming, and you often need to hold these structures in place whilst the specimen dries out - that is a definite advantage to micro-pinning!

Wednesday, 14 March 2018

Is it time to develop a ‘High Altitude Dipterists Group’?

I have felt for a long while that Dipterology in the UK was missing a trick because so few people do any field work at higher altitudes. David Horsfield and Iain McGowan have done a tremendous amount over the years, but they are the minority. Stuart ball and I have done a little bit – looking primarily for Gonathrus planiceps on Cairngorm, Glenshee and in the higher parts of the Pennines. In so-doing we have managed to find a few records of interest but in the course of many visits have only once found a single Gonarthrus! We believe that it is only found above 2,000 feet, so the numbers of potential locations are quite small outside Scotland. But, who goes high in England and Wales and makes a real effort to look for Diptera? 

Figure 1. Flush above Glenshee ski centre
The reality is that upland entomology is hard work and the range of species is quite small compared to a nice lowland woodland! Nevertheless, it is an important fauna and is one that is quite likely to be seriously affected by climate change. After all, our mountains are quite low and changes to the temperature profile could be dramatic. Some while ago, Stuart modelled the possible range of Cheilosia sahlbergi and predicted that it could be lost by the end of this Century! Those predictions come with a big ‘health warning’ but they highlight the possible plight of upland invertebrates.

Today, I was reminded further of how limited current recording is at higher altitudes. Martin Drake sent me maps of two montane Dolichpodids: Dolichopus maculipennis and Hydrophorus rufibarbis (Figures 2 & 3). They tell an obvious story of how poorly worked the uplands are! Although there are lots of old records there are frighteningly few modern ones. This deficit is almost certainly a lack of recorder effort.

Figure 2. Distribution of Dolichopus maculipennis as currently on the Dolichopodidae scheme dataset. The black dots represent most recent records.

Figure 3. Distribution of Hydrophorus rufibarbis as currently on the Dolichopodidae scheme dataset. The black dots represent most recent records.
Stuart and I have often discussed the idea of forming a ‘high altitude group’ to address this deficit. We are not as young and fit as we once were, but there ought to be lots of young entomologists just waiting for a challenge. I think in my 20s I could easily have been pushed into the mountains – especially if it had involved a bit of ropework and climbing. Most high altitude Dipterology simply requires a bit of strenuous exercise – so here is the challenge to the younger generation: how about looking high up for your Dipterological experience? The advantage is that the species range is quite small and there are lots of possibilities of short papers and articles on your findings – the literature is highly deficient.

In the meantime, I really ought to rise to the challenge of looking for upland Dolichopodidae and of course Platycheirus melanopsis and Cheilosia sahlbergi. The former was once known from the Lake District and I’ll bet it is still there! And what is there on the higher reaches of Snowdon, Tryfan and the higher peaks of North Wales?

Who said that all the low-hanging fruit had been picked? There is plenty to do looking at flush systems on different rock types and some nice ecology to be done. All it needs is a few energetic youngsters!

Sunday, 4 March 2018

Identification from photographs – an art rather than a science?

An article on testing the skills of Great Crested Newt Licence-holders was brought to my attention yesterday (as part of a wider circulation). A synopsis of a more detailed paper was published in ‘Inside Ecology’ (Online Magazine for Ecologists, Conservationists and Wildlife Professionals) and was titled Using online images for species identification with the follow-up comment: ‘How much reliance can be placed on the identification of a species using an online image?  In a newly published paper, researchers document the results of a study looking at accuracy and agreement of newt identification between experts…

This is an issue that is very close to my interests, even though it was dealing with a different group of organisms. I’m afraid it was extremely disappointing in many respects and made an awful lot of assumptions that are basic pitfalls of research. 
The first pitfall was that the researchers appeared to have fallen into the trap that an online image with a name against it is deemed to be correctly identified! Having spent literally thousands of hours examining online images of Diptera, I can say with total confidence that even the best sites contain wrongly identified images. What is more, if you send a correction these are very rarely taken up, so the photograph continues to be wrongly titled. Only this last week I found one on the NBN Atlas; I also found one on the site a couple of hours later. Not only were both the wrong species but also the wrong family!

It also happens in published papers – I’ve seen DNA profiles published for flies that are clearly assigned to the wrong family! Misidentification is rife and the online World makes it increasingly likely that misidentifications will be perpetuated into other records by the match the photo approach that is emerging as the modern norm.

There is a basic rule of thumb – if you want to identify an animal/plant/other item go back to first principles – can you see the defining features? Start by checking the family, then the genus and then the species. This problem also happens with specimens: I not infrequently find myself scratching my head over a specimen presented to me as ‘and I think I am right that this is …’ I then spend five minutes going around the houses before it dawns on me that I’ve taken it for granted that they have got the genus right! So, the moral of this story is that we all do it. BUT, if you are undertaking a detailed investigation into photographic identification you should at least make sure that all of the subject matter has been vetted by a recognised expert (and not just a GCN licence-holder).

The second pitfall was sample size. I vaguely remember being taught statistics at University. Or, at least, some poor soul had to try to get my defective brain to understand the basics of T-tests etc. The one thing I do remember is that sample size is critical and the smaller the sample size the less reliable the statistics. So, a sample size of 17 seems to me to be woefully inadequate for any scientifically rigorous analysis. Indeed, this size sample is so small that I am amazed the reviewers of the published paper did not raise an issue!

Then there comes the issue of how the sample group was assembled – it came from a call for volunteers. In other words, a self-selecting group and in no way a randomised and stratified sample. As such, this puts the results severely into doubt. Interestingly, the participants were asked to assess their abilities against those of their peers – that was illuminating! (Figure 1) I think that the message coming from this exercise is that ‘pride comes before a fall’. The one participant who stands out for me was No 17 who considered their abilities to be ‘worse than’ their peers and yet they ranked No 1 in terms of the performance in relation to study species (but sat in the bottom quartile for overall performance).

Figure 1. Ranking of participant performance in photo ID of newts - after Austen et al. (2018), Species identification by conservation practitioners using online images: accuracy and agreement between experts. PeerJ 6:e4157; DOI 10.7717/peerj.4157

This example highlights the importance of being aware of one’s potential failings. Who says we are an ‘expert’? If we call ourselves experts then by what reliable marker have we arrived at this conclusion? And, should we call ourselves an ‘expert’. I prefer the term specialist because ‘expertise’ suggests a level of infallibility. Not so – everybody makes mistakes, no matter how experienced they are! However, if there is one aspect that ought to set the ‘expert’ apart from the rest of the field, it is their ability to recognise their own fallibilities and not to take an identification beyond what can realistically be done in the medium concerned. If the characters are not clear, then leave the diagnosis at generic level.

Interestingly, the GCN study viewed uncertainty as a failing. I think it is anything but – it recognises the limitations of identifying an animal from an awkward angle and without the ability to rotate it and check critical features. Their analysis implies that it ought to be possible to identify everything from a photograph, but that is patently untrue. Not all photographs are top quality, pin sharp and high resolution. Equally, a photograph from one angle is often insufficient to make a firm diagnosis (perhaps even with newts – I don’t know enough about them).

Over-confidence is something that leads to misidentification. It reminds me of the occasional problems with participants in social media who don’t like it when a specialist will not take a diagnosis beyond generic level. Having been called ‘timid’ by one over-confident participant, it reminds me not to accept records from people who are over-confident. The tabulation of the GCN licence-holders reminds us of our own fallibilities.

Additionally, the study excluded contextual information. Now, I can understand why they might want to exclude such information; but that overlooks the critical point about identification from photographs. It may well be that the contextual information gave the game away! But then, does an ability to identify from photographs tell you a great deal about a licence-holder’s ability in the field? It may tell you a bit, but from personal experience I don’t think field skills and photo ID skills are totally inter-related.

When I started working from photographs I’m sure I made all sorts of howlers, despite having 20+ years’ experience at the time (I’ve now been doing online photo ID for about 12 years). Having a bit of context is often essential – date and basic geography helps to eliminate or embrace particular species. One of the reasons I am interested in photo ID is that as I assemble a bigger database it becomes clear how many records submitted to the HRS might be dodgy on phenology alone. I wonder, do newts that are found on land look different to those in water? I’ll bet they do because they won’t be in full breeding regalia! So, date context may be important in separating species.

All-told, I was underwhelmed by this study. It does, nevertheless, raise important questions about the challenges of making reliable identifications from photographs in a wide range of taxa. If there are problems with a small group such as newts, then the issue becomes many times worse when applied to, say, hoverflies or solitary bees that have multiple generations and seasonal as well as gender-related polymorphism. Inevitably, photo ID becomes an art as much as a science, but it depends very substantially upon good knowledge of comparative anatomy rather than painting by numbers!