Changes in data sources - a timely reminder

This morning I awoke to an interesting post from John Bridges on the UK Hoverflies Facebook page; he had been going back through my blog and picked out an article from 2012 in which I was extolling the possible benefits of photographic records to biological recording. To quote John, quoting me:

• For several years, I have been trawling the internet for photographs of hoverflies ----- So far I have extracted almost 9,500 hoverfly records ….............'That's about a weeks worth now.'

• During the mid-summer months, this trawl can take as much as an hour a day...............'I bet he wishes it still did?'

• Over 2700 records of hoverflies have been extracted for 2012 …................. 'Waiting for him after breakfast on a morning now'

• Trawling the internet allows me to undertake biological recording whilst maintaining my presence in the office................'How much spare time now Roger?'

That was just 5 years ago and it is a timely reminder of what has happened in just a few years. It is also something that those who use but don't generate biological records might reflect upon. In 2012 I saw photographic recording as an adjunct to the main source of records and simply a way of increasing my own productivity without disproportionate negative impacts on me! Other recording scheme organisers were more wary (perhaps wisely so) - not wanting their lives to be ruled by the internet and their recording scheme.

John's estimates of the numbers are a little bit out, but the overall thrust of his analysis is correct. For example, 9,500 records equates to about seven weeks worth of data extracted in mid-summer and roughly 25% of the total for 2016. During the summer months I dare not be away from the computer for more than a couple of hours - I do an hour or two first thing in the morning and then log back on at lunch-time (if at home) but definitely by 5pm at the latest - by which time I have a good two hour's of work to do. If I fail to do this the evening is a nightmare so it is a critical marker in my day's work. Then, after supper I often spend the rest of the night extracting data - during mid-summer posts are still coming in at 1am and there are times when they come in like a machine-gun! 2016 was the turning point, and had help not arrived I would probably have been a gibbering wreck by now.

Fortunately, the Cavalry arrived just in time - Ian Andrews and Geoff Wilkinson now help to spread the load, and there are other potential offers of help. The other huge help has been those FB members who now maintain their own spreadsheets. This is a massive improvement because it means that a wider community of members can help with ID (thus growing their skills and spreading the load on me, Ian, Joan and Geoff). I still look at every post, and will still comment on those that need one - I think it is essential that people who have taken the trouble to post get an acknowledgement at least from me (a 'like' at least).

The other thing my 2012 post did not take into account was iRecord. It did not exist at the time, but is also another part of the job today. Last year there were about 6,000 records that took several full days to work through - there is a post somewhere giving times and some basic statistics. This year there are about 10,000 to work through. This form of data submission is growing at a considerable rate and it is likely to require further administrative changes to keep on top of it.

Meanwhile, several recorders now maintain spreadsheets and also send me specimens to check (sorry I am behind on this job folks). I think this is a great way of recording because it broadens the range of species covered, but of course it is another layer of demand on the recording scheme. Meanwhile, spreadsheets arrive at an increasing pace - this year has been the busiest yet. I do the basic checking and formatting before they go to Stuart for importing into the database. Both jobs take a while, but I am pleased to say that we are pretty much up to date (I think there are 5 datasets on the Dropbox awaiting Stuart's attention at the moment).

So, would I go back to the 2012 scenario?

Emphatically not (although I would like my life back)!

The growth in popularity of Facebook Groups (not just Hoverflies) has seen an unprecedented leap in the numbers of people contributing records and acquiring skills. We can produce data for the HRS to show its impact, but I wonder how many other schemes are in a position to do so? That growth will hopefully translate into the development of new people who will ultimately take over the running of the popular schemes (we must think about the very long-term).

Equally importantly, photographic recording has actually started to help to unravel some aspects of species' ecology that we would not otherwise have had. True, it is also creating a skew in the data that I have written about, but we can deal with that provided we still have a pool of traditional recorders who retain specimens for critical checking.

What I would like to see is a further shift towards people managing their own datasets and using the Facebook pages to deal with cases where they are not sure. That will doubtless happen over time and, of course, it needs to because the time of the 'Resident Team' is finite and we really must try to devote it to developing newcomers and embedding skills in the wider community. John, himself, shifted towards managing his own dataset a long while ago - and has contributed a huge number of records this way. In only three years he has become one of the all-time major contributors (there are several others who will do the same). We would not have had this improvement in recording without the advent of digital photography, the internet and social media. So, whilst there has undoubtedly been a massive change to my life, it is largely positive because so many more people get pleasure from hoverflies, are learning new skills and are forming a community that will hopefully last long after I am gone.

Making the most of very little funding?

For ten years I ran Dipterists Forum's field meetings programme - at least three meetings a year, all of which were 'residential'. The Summer field meeting was usually organised around a venue such as a field centre or University Campus, whilst the Spring and Autumn meetings were organised around guest houses and hotels, with the onus on members to find and book their own accommodation. Latterly I have also found a chain of hotels that has a small number of single rooms and which can accommodate our tiny party of Autumn specialists.

The big stumbling block was finding accommodation at a reasonable price. My aim was to secure a week's meeting for no more than £360 half board and with a common 'work room'. As time went by it became increasingly difficult to find such venues and in many cases I just could not manage to get anything because the Universities started to treat groups such as ours as 'Conferences' with appropriate 'Conference' rates. In the end I gave up running the summer meeting as I had run out of steam.

So far, DF has managed to continue the summer meeting programme (for 3 years) but I know it is a struggle to find venues at sensible prices and DF has had to subsidise some of the costs. That is an unsustainable long-term scenario so an alternative needs to be found.

It would be a shame if DF Summer meetings were to cease, because they offer a fantastic opportunity to get 20-30 of the country's leading Dipterists to look at an area. In some years they generate as many as 8 or 9,000 records (except in bad weather!). Over the 40+ years that these meetings have been run, they have been instrumental in the discovery of many dozens of 'New to Britain' and even more important second, third and fourth records. Importantly, the way DF works is to encourage newcomers and in recent years bursaries have been provided to allow two or three aspiring Dipterists to participate at subsidised rates - thanks to an anonymous donor and to the income from our WILDGuide 'Britain's Hoverflies'.

Will these meetings continue? We must hope so. BUT, as time goes by it gets harder to find accommodation and meet the bureaucracy of securing access permissions and, increasingly, providing evidence of insurance. Meanwhile, as costs rise, it is inevitable that the meetings will become out of reach for the less well-off. It would be terrible to see this sort of meeting become the preserve of the rich, pushing biological recording back towards the 19th Century when it was the preserve of the 'men of independent means'. I expect similar problems face other societies.

Getting 'Bangs for Bucks'

So, if there is thought given to funding and getting more bangs for your bucks - what about finding a way of supporting such field meetings - a subsidy provided records are received by a given date? If there are organisations that feel that they could support a targeted approach then maybe there is mileage in forming a partnership. For example, the three Country Agencies all want records from SSSI; LRCS want records from their area, and maybe there are others who would also see some merit in getting DF to visit their area. The main point is to try to get broad coverage, so there would need to be a good range of sites to visit - a team of 20 can cover a lot of ground in a week!


I also think there is a lot of sense in some of the societies working together to make these sorts of meetings happen and to ensure that when they are there there is an interchange of specimens. The DF Summer meeting has an annual event - the Honey Pot Challenge - a pot of Andrew Halstead's very excellent honey as prize for the person who generates the most records of sawflies in the week. It is a keenly contested prize, surprisingly so when you bear in mind the havoc that a sawfly can create in a pooter full of flies! I am sure other traditions could be generated and that these in turn might harness the enthusiasm of people to find a bit more than just their target interests; after all, when sweeping we all come across other taxa that may be of immense interest to other schemes.

And, if anybody is thinking about HLF bids, then maybe developing a programme of support for the active recording groups to go 'square-bashing? I have described some of my trips in this blog - it costs me about £350-500 per week to do this sort of survey - so it is inevitable that the furthest-flung places will get very little effort and those closer-by but under-recorded may stay so if the costs are too high. When I had work, I used to take myself off for five or six weekends a year and cover poorly recorded (and often very dull) parts of the country. Now, without work, I cannot afford much and try to go to places where I will enjoy the fieldwork and the scenery!

Is better funding the answer to improved biological recording?

My post yesterday generated an interesting thread on the issue of funding biological recording. Is this the solution to an apparent dearth of records in taxa such as slugs or ground beetles; or for that matter hoverflies, bees or other pollinating insects?

I think the issue is a bit more complicated than simply money. For a start, you have to be very clear what you want data for, before throwing large amounts of money at it. In yesterday's example it was studies into a Section 41 species, which arguably means money needed to commission extensive single-species surveys, which are probably the only way of generating the presence/absence data that might help some aspects of autecological work. However, even those sorts of studies will not say that a species is absent, they can only say that it was not found when looked for, so a level of caution remains. Nevertheless, money could be injected into surveys for Section 41 species [the species in question (Carabus intricatus) was a species targeted by English Nature's 'Species Recovery Programme'].

Do targeted surveys solve the problem though? I recall one classic study into the 'Phantom Hoverfly' Doros profuges that lasted 3 years and in the entire time not a single record was generated. One has to conclude that it was probably not the greatest 'value for money' but the exercise did show how difficult it is to gather information on some of our rarer, or perhaps more elusive species. From what I can see from the data, Doros profuges is likely to be doing something that makes it scarce, rather than it necessarily being all that scarce where it occurs.

Current data needs

The big challenge at the moment is how to reverse the massive overall decline in invertebrate life. There has been a lot of noise about data derived from a 27-year German Malaise Trap programme. That noise also implied that the UK lacked the necessary data to detect declines (apart from butterflies and possibly moths). The German work was based on traps run by 'amateur' entomologists who conducted the massive task of sampling, sorting and identifying each year's material. The people who did this were not the 'average man on the street' but a highly skilled team that includes some of western Europe's best taxonomists and conservation scientists. The only reason you would call them 'amateur' is that they did the job for nothing and probably would not have taken it on if it was a paid task because it is such a huge and often un-rewarding job.

Could such a similar dataset have been assembled in the UK? Well, yes it probably could, had there been the willpower, insight and sheer determination by a big enough group of individuals. But there is the rub - a big enough group of individuals that see this sort of work as their priority. Running Malaise Traps is no easy task; indeed, any project that samples systematically and in large volumes is not a job for the faint-hearted! I regularly provide identifications for academic projects that run Malaise Traps and it takes an awful lot of time to do the identifications, let alone the basic sorting.

Yet, as I have previously written, I think there is a case to be made for establishing a Malaise Trap programme (posts of 11 & 12 November). The crucial point about this sort of programme is that it needs to run for at least 10 years before any meaningful outputs emerge, so if it were to be a funded programme the sums involved would be astronomical. To use an example, I ran the Dungeness Invertebrate Survey using pan traps and pitfall traps in the late 1980s (with Mark Parsons). It ran for two years and would have cost somewhere in the order of £80,000 including support costs. In today's money that would probably be closer to £200,000. It depended very largely on Recording Scheme organisers to do the identifications, so the real cost would have been a great deal higher if their time had been paid for at consultancy rates. I rather doubt any scheme organiser would readily volunteer to help on this sort of project today because the demands on their time are so much greater now. So, what would the German Malaise Trap programme have cost? Many millions I suspect!

So, what are the alternatives?

UK biodiversity data is predominantly derived from the work of countless 'Citizen Scientists' that range from the technical specialist and leader in their field, to the person who enjoys a walk in the countryside and posts their resulting photographs on iSpot in order to find out what they have seen. Each has a place in the process, but the whole thing is utterly dependent upon the very small number of people who have acquired the necessary technical skills and are willing to share those skills with a wider community; not every specialist will do this and I know a lot who won't go near photographic recording. Indeed, it has  been commented to me by various specialists (on several occasions) that I am wasting my time and I would be doing more good engaging in private ecological or taxonomic studies.

Assembling the data from these sources is no small task. To the relative newcomer it may appear to be a random and unfathomable process that fails to take full account of modern technology. Unfortunately, what we see today is the result of 150 years or more of recording using the most viable means of the day:

• Until the 1970s notebooks and diaries plus odd notes in Natural History journals were the only way to disseminate data. These, plus Museum collections provide the foundations for what we know about the history of our wildlife assets. Some of these repositories have been converted into modern accessible data, but there are vast amounts still to do.
• In the 1960s and early 1970s we saw the growth in biological recording closer to its current form. The BSBI plant atlas was perhaps the crucial model, but by then some natural historians were running their own card indexes - I recall the remarkable AA (Tony) Allen who always seemed to be able to write a note quoting various records that he had clearly noted in some voluminous index (or he had a brain the size of a planet). By now, early computing was making it possible to produce dot maps and these became the rage for about 25 years - national and local atlas schemes were in vogue. Why? because we did not have the internet and the printed word was the only way of making information accessible.
• By the mid-1980s personal computers were becoming available to the masses, and the more adventurous (or able) designed their own databases, that morphed into the current pillar of many biological records centres: RECORDER.
• By the 1990s, personal computers had become sufficiently  accessible (and powerful) that biological recording schemes started to take on the data management process themselves. They did so because there was totally inadequate central funding for data management - in the case of the Hoverfly Recording Scheme we digitised about 175,000 records from record cards - who now would even know what a RA33 or a Gen7 was? It was darned slow and tedious work but done by volunteers because there was no money (especially after 1991 and the dismembering of the NCC).
• Then came the Rio Convention and the development of 'Biodiversity Action Plans'. A whole industry of BAP emerged with relative novices running around compiling great tomes on what occurred where and what was important in a local context. The 1990s was the decade of BAP planning ('plans, plans and more b..... plans' I remember was the catchphrase of one ports industry commentator). BUT, this episode highlighted the need for better co-ordinated data management and we started to see the growth of bespoke 'Local Records Centres'. This was partly driven because there was an obvious local need as the Habitats Directive started to bite and local authorities and developers needed to know where protected species occurred. The desktop computer had come of age and it was being put to good use in biological recording - less than a generation ago.
• A network of Local Records Centres is all well and good, but biodiversity reporting demands central access to information; hence the need for better co-ordination and the growth of the NBN and its online facilities; hence too the development of GBIF at a global scale. The advent of the NBN has been accompanied by a massive growth in the facilities available for data capture - major investments by the Statutory Agencies and some NGOs.

So, here we are today after a long journey of system development - a great system for acquiring and processing data. We have iRecord, innumerable specialist online data acquisition systems ranging from the BTO's excellent 'Birdtrack' to the Mammal Society's online facility. They have generated a great deal of new interest in biological recording because it is relatively easy to input data (and you can re-access your records without having to resort to pen and paper or personal spreadsheet if you so wish).

But, biological recording is not only about acquiring and disseminating data. It is about feet on the ground, hand lenses, microscopes and so much more. If you want data you have to have the skilled technicians to generate it! Where are they? 'Citizen Scientists' of course!

Data suppliers - the reality

Most recording schemes rely on a minuscule number of diligent and technically  competent recorders. In the case of the Hoverfly Recording Scheme that comprised just 20 people across the country who supplied 50% of the data up to 2011. Since 2011 the situation has changed markedly, with the numbers of records arriving each year having doubled from between 25-30,000 to 50-60,000 records. BUT the numbers of recorders who do the tricky identifications has not risen in line - if anything they have dropped - we have lost several of our most diligent recorders in the last decade - the Grim Reaper marches on! Meanwhile, as I have previously shown, this change in recording effort is affecting the composition of the data and therefore the story they convey, if incorrectly interpreted.

Also, now, we rely on technical specialists such as me, and the 'Resident Team' on the HRS Facebook page to provide identification and verification services. This is a new task and one that has ballooned in the past five years. We have no greater capacity but far more demands on our time. So, instead of sitting at the microscope identifying material beyond the limits of my own scheme, I sit at the computer identifying and extracting records of hoverflies - the HRS gains records (volume) whilst other recording schemes lose out!

What would increased funding do for biological recording?

My example of survey costs tells a lot about what the costs are for assembling data. Bearing in mind there are perhaps 50,000 plant and animal taxa in Britain, and there are about 2,900 land hectads (10km squares) the costs of improving data by commissioned surveys and increased numbers of technical specialists would be immense. And, that is BEFORE we enter the marine environment where the costs rocket to immense figures. What is more, to achieve that sort of skill level you need skilled trainers - the same people who currently run the recording schemes and provide the validation and identification services. There are only 24 hours in a day and those people, by and large, are already operating at capacity - there is no spare capacity.

So, yes you could throw money at biological recording but in the end it boils down to a dearth of technical specialists and ever-increasing demands placed on those who have until now been willing to shoulder the task. Will that continue? Well, I for one would like to retire from running a scheme - but can/will only do so when we have replacements lined up, willing and able. It is a daunting task and not one that is likely to appeal to anybody with aspirations to have a family or a life!

Time to set up local Diptera Groups?

There are lots of species of Hoverfly and other Diptera that are eminently findable but are under-recorded. Some will only be found by sweeping and retaining specimens of similar species, but others could be sought by visual searches. This winter is an ideal time to start to develop local groups to seek out species that have either not been found or might be re-found in a particular area. Working at a County level is probably the practical way of organising but one could also do this at a regional level.

There are already some great exemplars. In Northamptonshire there is a local group that has weekly field meetings during the spring and summer. In Devon there is a group that meets (I believe) on a monthly basis. Opportunities exist elsewhere.

What about a 'New Forest' group, a 'Black Country' group or a 'Thames Estuary' group? More adventurous still - a 'High Altitude Group'. Developing and leading such a group is not dependent upon high levels of skills as a Dipterist but upon bags of enthusiasm and a willingness to act as a fulcrum around which others gather. That is a great role for relative newcomers - perhaps one for recent graduates wanting to make their mark? What is needed is an ability to enthuse and create an inclusive group whose meetings are not only instructive but also social. Don't worry if the group includes people with limited skills or experience - what you need to think about is creating a happy atmosphere and to set targets that are achievable and to which everybody feels they have contributed.

I wonder about a 'top ten' of targets for 2018? Here are a few ideas (over 10 - I can still count!)

1. Anasimyia interupta - grazing marshes and the river valleys of Cambridgeshire and Norfolk.

2. Callicera rufa - creating and monitoring artificial rot holes

3. Callicera spinolae - scattered records across East Anglia but possibly more widespread - surveying places with old trees and Ivy in September as a 'safari'.

4. Caliprobola speciosa in the New Forest and at Windsor Great Park.

5. Chrysotoxum vernale on Dorset heaths

6. Doros conopseus in Yealand Allotment and at Martin Down (Wiltshire)

7. Lejops vittatus in Essex, Kent, Pevensey Levels, Somerset Levels, Gwent Levels and Norfolk. (also perhaps look for Hybomitra muelfeldi and Atylotus rusticus)

8. Microdon analis on Surrey and Hampshire heaths

9. Microdon devius on the North Downs of Surrey

10. Microdon mutabilis larvae and puparia - north and western Britain but perhaps also the Welsh and West Country coasts? They live in slightly different places to M. myrmicae which can be found in tussock nests of the ant Myrmica scabrinodis.

11. Odontomyia ornata and other wetland species - various grazing levels but also scattered wetlands inland. One of several possible targets linked to wet ditch systems and pond edges.

12. Pelecocera tricincta on the Hampshire and Surrey heaths - there are lots of old records but limited recent records for places such as Chobham Common and Hankley Heath.

13. Parhelophilus consimilis - Somerset Levels and maybe other grazing marshes

14. Platycheirus melanopsis - the higher peaks of the Lake District and Scotland

15. Stratiomys longicornis - coastal sites. Maybe look for other saltmarsh specialisties such as Atylotus latistriatus?

16. Gap-filling in areas such as the upper Pennines, parts of mid-Wales, southern Scotland, and of course the many Islands. 

Any takers?

My targets for this year are to find new sites for Microdon mutabilis (and secure some material to try to help to work out how to split this and M. myrmicae. I have also got plans to look for Hammerschmidtia ferruginea away from its Speyside haunts and am hoping to find a few more sites for Lejogaster tarsata in the Iris flushes of the west coast of Scotland.

Don't believe the database!

I spent a little while investigating GBIF to follow up on Stuart Roberts' comment on the NFBR Facebook page that relatively few countries regularly upload to GBIF. To try to find a bit of context to compare UK data with northern Europe I looked at Eristalis cryptarum which in the UK is confined to three or four 10 hectads in southern Dartmoor. It was formerly present in the New Forest and at Studland, and there is a scattering of very old records from south-west England (Map 1).

Map 1. Distribution of Eristalis cryptarum according to held and scrutinised by the Hoverfly Recording Scheme. Black circles = 2000 onwards, Grey = 1980 to 1999; and Open = pre-1980.

Turning to GBIF, it is clear that E. cryptarum is widely distributed and largely Boreal or sub-Boreal across the Palaearctic (Map 2). I assume that the majority of records are correctly identified but of course there can be no certainty! Anybody working in another country might make the same assumption but would they be right? I'm afraid not! And where is the obvious problem? The UK, of course!

Map 2. Global distribution of Eristalis cryptarum according to GBIF as on 26 November 2017.

What on earth does he mean? I hear you ask: after all the UK records come from the Hoverfly Recording Scheme? Unfortunately they don't; all sorts of data are put on GBIF, verified and un-verified. So what is happening in the UK? A blow-up of the map (Map 3) tells the story very clearly.

Map 3. Distribution map for Eristalis cryptarum in the British Isles according to GBIF as on 26 November 2017.

I cannot comment on the Irish records; I am not aware of E. cryptarum in Ireland but would be happy to be corrected if there are genuine records. What I do know is that there are no records from Scotland, nor are there records from East Anglia. Both of these records are clearly erroneous, so where do they come from? I've not managed to work out where the East Anglian record comes from, but the Scottish one is amongst recent records compiled by Buglife! Where is the quality control before putting data onto the national and international forum? My guess is that both records are misinterpretations of colloquial names - both E. cryptarum and Sericimyia silentis share the same name: Bog Hoverfly.

This is of course an object lesson in why the rigid structure of Latin names exists - why try to usurp it with names that cause confusion? Meanwhile, beware outlying records that just don't look right! On which theme, I wonder about the record from the Pyrenees but would not dismiss it because there is the possibility that the right environmental conditions obtain at some altitude there. So, for UK distribution I would avoid any compilation of data from sources other than the HRS - we have problems but do normally manage to sort out the obvious glitches.

Lejops vittatus - has it declined or is it overlooked by lack of recording?

Lejops vittatus is a fairly easily identified species of Eristaline, but seems to be rarely recorded. It occurs in brackish environments, primarily in the ditch systems of the grazing marshes of Kent and Essex, the major coastal wetlands of Norfolk and grazing marshes of Somerset and Gwent. There is also a very old inland record that appears to be reliable (Figure 1). It is one of a group of genera whose larvae are aquatic and live deeply submerged and breathe through an extendable spiracle (rat-tailed maggots).

Figure 1. Distribution map for Lejops vittatus. Black circles = 2000 onwards, grey = 1980 to 1999 and open = pre-1980

What I had not previously relised was that the UK might be THE stronghold for this species in Europe if the GBIF map is anywhere near accurate. It otherwise seems to be coastal within the Baltic and there is a more central European record that I suspect is along the Danube (Figure 2). What this map does not tell us is that data on GBIF is somewhat patchy - there are good datasets for Germany and The Netherlands, but not for France, so the map is potentially somewhat misleading!

Figure 2. Northern European distribution of Lejops vittatus according to GBIF on 27 November 2017.

Analysis of the HRS data suggests that there has been a significant decline since the 1980s (Figure 3) but the data are very sparse, so I would treat this trend with some caution. What I think the trend tells us is that there may have been relatively little activity by skilled recorders in key areas. I have only seen this animal twice in 30+ years of recording; once in 1985 on the Somerset Levels and again at Seasalter in 1991. However, I have not looked very often so I don't think my experience is anything to go on! It is noteworthy, however, that the 1991 record arose because I was intensively surveying the ditch systems of the North Kent marshes and always had my eye open for this species. I think it is genuinely rare on the Kent coast!

Figure 3. Frescalo trend for Lejops vittatus.

Looking at the phenology histogram (Figure 4), it seems to me that this species has quite a narrow emergence window centred upon late June and early July. The very early and very late outliers in the data need to be more thoroughly investigated, although there is just a possibility that they coincide with exceptionally warm years when there might have been a partial second generation.

Figure 4. Phenology histogram for Lejops vittatus based on all records in the HRS dataset.

This one seems to me to be a potential 'target species' for Dipterists based in Somerset, South Wales, Norfolk, Essex, Kent and East Sussex. It should be identifiable from photographs, so that makes it a viable project for the many photographic recorders that live in these parts. I would add that whilst in such places it is also worth making an effort to record the Soldierflies and Horseflies - there are also some very rare and habitat-specific species that are likely to be under-recorded.

A bit of market research

It is nearly 50 years since the second edition of 'Flies of the British Isles' by Charles Colyer and Cyril Hammond. It is the book that first got me interested in flies and I am sure was the catalyst for so many of today's Dipterists. Who could resist the fantastic photograph of Volucella zonaria on the cover and Cyril Hammond's fabulous drawings and paintings? It was also written with a charm and authority that would be hard to repeat. Sadly, it went out of print many decades ago and can only be obtained second hand. Most copies are pretty well 'loved'. Unfortunately, Cyril's paintings were lost when he died and there is no way that they can be re-used.

The book itself, whilst still very readable and informative, is also considerably dated. Our knowledge of the British fauna has expanded by perhaps as much as 1,000 species since the original edition was published in 1951. The taxonomic arrangements have changed and so too has much of the nomenclature so, although a 'must have' on the library shelf, it is probably not the volume you would turn to now if you wanted to get 'into' flies? In actual fact, it is probably still the book to turn to for a general introduction! There is the excellent, but largely unillustrated, 'Dipterists Handbook' which is a valuable well of knowledge, but lacks such things as keys. There is also Pjotr Oosterbroek's 'The European Families of the Diptera: Identification, Diagnosis, Biology', which is the only readily accessible key to the European families unless you start to invest in the weighty Manual of Palaearctic Diptera, which is beyond the pocket or the shelf space of the average novice! In a similar vein, Stephen Marshall's 'Flies: The Natural History & Diversity of Diptera' is a huge shelf-filler, colourful and informative but would be difficult to use in a UK context.

A replacement for Colyer and Hammond has been long-needed and has been the dream for several of us for many years. It is a daunting task that is not helped by the potential challenges of sourcing the illustrations needed for keys and family accounts. Stuart and I have frequently discussed the idea of such a project but nothing has come of it. Conceptually, it does not really fit the WILDGuides model that we used for 'Britain's Hoverflies' because it needs to be big enough to accommodate well-illustrated keys. We have done a bit of preparatory work and Stuart has been photographing fly wings for a couple of years - he has about 50% of the families covered already!

After a long period of quiescence, we are now talking to a possible publisher and are building a team to write it - we need a range of expertise and will be working with Dr Tony Irwin (formerly Curator at Norwich Museum) and Dr Graham Rotheray whose work on Diptera larvae has been inspirational both in the UK and in many other parts of the World. Additional peer review will be needed and we are confident that this will be available through Dipterists Forum. All four of the team are well-versed in the challenges of producing user-friendly keys and guides, so we think we have the right foundations for a great product.

As we start to work up our ideas, we need to think carefully about what can be achieved. Such a book would be quite large and, if illustrated in colour, might be quite expensive to produce. It therefore makes sense to try to understand the market. What is the ceiling price that would dissuade the aspiring Dipterist from buying it? I believe that 'British Soldierflies and Their Allies' currently sells for £36.00 direct from BENHS for non-members and have seen it going for £49.00 from Amazon! I imagine we might be looking at a similar bracket of price. Also, what would potential purchasers place more emphasis on: descriptive text, keys or colour plates?

Our basic outline at the moment is as follows:

1. It will be composed of 3 sections:

• A substantial introduction. This would cover areas needed to understand the keys such as explaining the taxonomy and anatomical terms. An account of their life styles, biology and ecology of both adults and larvae, including treatment of medical and economic importance. Some very general coverage of the flies of macro-habitats.
• Keys to the 106 families. These have been rigorously tested and developed over the past 10 years. This key has been used in previous FSC courses run by Stuart Ball & Roger Morris as well a substantial number of other courses run by Dipterists Forum.
• Descriptions of each family intended to be laid out in double page spreads with text on the left-hand page facing illustrations. The detail in each family description will vary, with some of the more obscure, small families perhaps having a half page with one illustration whilst the larger and better known families (especially those where there is a Recording Scheme) better covered with more text and several pages of photographs. Family descriptions will include coverage of the larval biology where known and a header summarising things like the number of species on the British list, their size range, the ease or difficulty of identification and whether it is covered by a Recording Scheme.

2. It would NOT aim to cover all species, even in popular families, but should be regarded as a companion to such guides as the Larger Brachycera, Syrphidae and Tipuloidea.
   
   
3. It would be illustrated by a combination of field photos, detailed photos of preserved specimens and line drawings to highlight specific features. It may not be possible to obtain field shots of some of the more obscure families especially where the species are very small.

We cannot be sure about its dimensions but we favour B5 format or thereabouts. At the moment we are thinking of a volume of around 350 to 400 pages, ideally full colour, but it may be necessary to use two-colour or even black and white in the key in order to reduce production costs. Inevitably, it will have to be perfect bound and in a soft cover as case-bound is likely to raise costs too far.

This is probably a 'once in a generation' opportunity. If the project finds a home (we have renewed hopes), it will fill a big gap in the literature. Our intention is to produce something that will last for several decades but we do need to produce a book that sells sufficiently quickly for the publisher not to incur long-term storage costs and also to recoup what is likely to be a significant investment over a relatively short period (i.e. a few years). If we can secure a publisher (it will probably have to be a 'not for profit' venture) my guess is that we are looking at a lead-in time of 3-4 years during which Stuart and I will probably be chasing madly around the country trying to source fresh specimens for the necessary photographs. We will doubtless also be approaching some of the very excellent photographers who publish on Flickr etc for suitable images!

Difficult taxa - should we believe the trends?

In my previous posts I have hopefully shown some of the challenges that we face when trying to interpret trends. Simply taking statistical outputs and accepting the results is generally unwise. One needs to understand what is happening within the data. As we have progressed with the revised atlas, I have therefore gone back to Stuart with a series of questions. The Frescalo outputs tell an important story but, as we have seen already, there are factors that may be having a profound effect on the results. Changing recorder methods are one factor that we can detect by separating off records derived from photography but here is one that confounds the basic analysis.

In my experience, Pipiza noctiluca is a very common species. It does visit flowers, but is far more commonly seen sun-basking on leaves - I favour elm, sycamore and lime for monitoring. On the right day in my local woods I can see maybe a dozen or more, mostly males. I usually retain a broad sample of specimens because they are so similar that it is quite possible to get two or even three species in the mix. It was in this way that I picked up the first British record of Pipiza quadrimaculata this spring (still to be written up and published). Taking a broad spectrum of Pipizines often adds species within Heringia and Pipizella as well. I find many of them to be pretty common, but often have a lot of difficulty being sure that I have actually got P. notata (bimaculata) and not another form of P. noctiluca!

So, what do the outputs tell us about Pipiza noctiluca? It all looks pretty clear (Figure 1)  - there has been a significant decline! But has there? Figure 2 where the same Frescalo analysis has been run on the whole dataset and then with photographic data excluded changes matters, as might be expected (Figure 2).

Figure 1. Trend for Pipiza noctiluca based on Frescalo analysis of all data.

Figure 2. Trend for Pipiza noctiluca based on Frescalo analysis for all data (blue) and with photographic data excluded (red).

The problem I find with both of these outputs is that one can roughly eye in a regression line but it is clear that there have been a number of very marked peaks. Unlike data for wetland species that has a spike associated with the major NCC surveys of Welsh Peatlands and East Anglian Fens in the late 1980s, the peaks here are a bit different. Is there something happening with recorder activity and perhaps changes in who is active and where they are active?

Figure 3 shows the current state of our knowledge of distribution of Pipiza noctiluca. It tells an interesting story. For example, in the 1980s and 1990s there was tremendous activity by a small number of very active recorders who covered all taxa. Dorset and Somerset were extremely well covered, as was Surrey and so too was the Sorby area. Several of those really active recorders have died or become too unwell to continue recording; others, such as me, have moved. There is also one recorder who is still very active, but whose records we don't have for the past 20 years (although this may be rectified soon).

Figure 3. Current distribution map for Pipiza noctiluca. Black symbols indicate the latest record dates from 2000 to date, grey - 1980 to 1999 and white - before 1980

In this instance, if we really want to understand what is happening, we probably need to look at the peaks and how they relate to activity by individual recorders; or whether in fact there is any correlation? Peaks do seem to be somewhat repetitive, so perhaps there is another environmental factor at work? Alternatively, perhaps we are just seeing bursts of enthusiasm followed by the inevitable misery of struggling to be sure one has correctly identified yet another form of P. noctiluca!

Changes in recorder techniques - can we detect differences in the dataset?

I have long felt that the shift away from records based largely upon specimens to records based on non-lethal methods such as photography was likely to be influencing the outputs of analyses to investigate trends in species' abundance. Whilst revising the text for the Provisional Atlas, I became acutely aware that some of the trends did not seem to fit my perceptions from field work and from monitoring the UK Hoverflies Facebook page. I therefore suggested to Stuart that it would be helpful to run two separate analyses; one for all data and the other for a subset of the data that excluded known photographic records. The results are really very interesting and can be summed up as a table (Figure 1).

Figure 1. Permutations of possible trends in the HRS dataset and in a subset that excludes photographic records. The final column highlights whether the permutations were found in analysis.

I think the overall results need to be published in the peer-reviewed press because they show how research teams must treat trends with caution. I expect that all of the graphs will become available at some point once we have decided how we might use them in the provisional atlas but probably not readily apparent in any printed version because of the cost of printing in colour. We can of course do so as a pdf without any problem. Here are a couple of examples:

Figure 2. Trends for Cheilosia proxima, All records in blue and with photographic records excluded in red.

Figure 3. Trend for Cheilosia impressa. All records in blue and with photographic records excluded in red.

Figure 4. Trend for Epistrophe diaphana All records in blue and with photographic records excluded in red.

Interpreting Sphaerophoria - or can we?

Today, I went through the species accounts for the genus Sphaerophoria, which is one of the more challenging genera for the student of hoverflies. Most records have to be based on males, because there remains quite a lot of uncertainty about the identity of females.

In my experience, most Sphaerophoria fall into two groups. One is largely associated with ericacious heaths and is substantially northern and western in distribution, or is confined to the major heathlands of Dorset, Hampshire and Surrey. It is chacaterised by S. batava, S. fatarum, S. philanthus and S. virgata. The main exceptions are S. scripta, S. interrupta, S. loewi, S. rueppellii and S. taeniata which are mainly grassland and wetland species. Some have clear distributions (e.g. S. tarniata and S. ruppellii) and others such as S. interrupta and S. scripta are widespread and more difficult to fit to a habitat.

So, what is happening to this genus? Quite a few appear to be declining, especially those that are associated with ericaceous habitats. Can we be sure that there have been declines? Anecdotally, I certainly see far fewer S. fatarum and S. philanthus than I used to, and I don't see the numbers of S. batava and S. taeniata that I used to. Part of the reason for my experience is that I no longer work the Surrey heaths where so many of these species occur. BUT I do spend a lot of time in Scotland and I am always pleased to even find a Sphaerophoria. Perhaps I go too early in the year? or perhaps something is happening?

So here are a few maps. Each is as yet un-edited for doubtful records so there may be changes, especially in the square spots which are NBN records which are often very doubtful:

Each map presents a few problems, but the main one is whether the decline in coverage is real or follows a general drift away from difficult taxa. The surprise, therefore is S. taeniata, which seems to be holding its own, at least in terms of coverage. Meanwhile coverage for the other four is clearly declining. There might be a range of reasons, however:

In the case of S. batava, S. fatarum and S. philanthus, these are species that generally occur in ericaceus communities, which in southern England are most widespread in Dorset, Hampshire and Surrey. Both Dorset and Surrey no longer get the attention they once did from recorders who looked seriously at Sphaerophoria. Dave and Ted Levy did a huge amount of work for their Dorset and Somerset atlases, Whilst Graham Collins and I did a great deal in Surrey at the same time. This year, we learned that Ted Levy was retiring from recording, having been unwell for several years, whilst I left Surrey many years ago. So, it is likely that these combined factors may have affected records from southern England - lots of records in the 1980s, but very few recently. BUT, what about Scotland? I make an annual pilgrimage and do a fair bit of recording there. I see very few Sphaerophoria but then perhaps I am going too early or too late in the year?

Then, what about S. rueppellii? It is a classic 'Thames Estuary' species but is not turning up in the numbers it used to. Unlike many of this genus, it can be identified from good photographs but is not often reported (we do see mis-identifications quite frequently). Perhaps it is declining? I suspect something is happening because the map for S. interrupta seems to indicate quite a significant reduction in records from south-east England. As this is the commonest species after S. scripta, and it does seem to have a significant northern and western distribution, I wonder whether SE England is becoming unsuitable for it. If so, my instincts are that this is a result of climate change and in particular periods of intense hot weather and drought.

So, do the maps and trends tell us something about how reliant we are on a small cohort of specialist recorders, or is something more insidious happening? I really don't know!

Interpreting data: Portevinia maculata

One of the big benefits of a developing network of new and enthusiastic recorders is that it is possible to cover new ground and look for species that are relatively easy to identify and find.

Portevinia maculata is one such species. Its larvae live in the bulbs of Allium ursinum (Ramsons or Wild Garlic) where they exist from late May through to early April. Adults emerge after a brief spell as a puparium and males (see photo) can be very abundant sitting on the Ramsons leaves for a short spell between late April and early June. We can therefore make use of this species biology to test the reliability of records and can also see how recording efforts have changes as people have become more interested in hoverflies.

Portevinia maculata - male (photo by John Bridges)

 The statistics tell us some interesting stories:

Figure 1. Trend in frequency of records

Figure 1 clearly shows how levels of recording remains substantially constant until around 2011 or 2012, after which they have changed dramatically. This cannot be a result of the plant spreading, as it is largely associated with older woodlands and does not move quickly. Nor is it likely that the insect has moved dramatically. It was always relatively easy to find and when looked for in new locations was usually located if sufficient plants were present and repeat visits made to coincide precisely with what is a very short emergence period. The map, Figure 2, shows the current situation.

Figure 2. Current distribution of Portevinia maculata (to 2017)

And then comes the phenology histogram (Figure 3). Most of the records sit tightly between early April and the middle of June. Experience with the UK hoverflies Facebook group suggests that the earliest dates are indeed around the end of the first week in April and that by the second week in June it has disappeared, even from Scotland. So, we must start to question outlying records in March and from mid-June onwards. We can probably discount the March records because the Ramsons won't have properly emerged and the insect is likely still to be a larva or a very early puparium. Beyond the middle of June it is highly unlikely that adults will be found (possibly the odd female into early July) and the larvae are first or second instar, so absolutely tiny and unlikely to have been found. So records within these timeframes can, with substantial confidence, be logged as erroneous.

Figure 3. Phenology histogram for Portevinia maculata

This is a nice example of the sort of problems one has to consider with all datasets, but is helped because the animal and its associated plant have very well-defined life cycles that make it relatively easy to interpret the data. Where we have less biological information it is much harder to make definitive statements and to question records.

Interpreting data: the problem of Platycheirus

Platycheirus  is one of the largest and more perplexing genera of hoverflies in Britain. There are often good and relatively straightforward male characters (on the front and middle legs) provided you know where and how to look (at high magnification). Females are often much more difficult, with characters that are somewhat subjective and open to misinterpretation: I know they give me problems, so I suspect they give others problems too! (The same applies to Melanostoma).

I have already highlighted the problem with female immarginatus/perpallidus but there are others such as the split between females within the clypeatus complex (clypeatus, europaeus, occultus, and  ramsarensis) and in the peltatus complex (nielseni/peltatus especially). These problems mean that one has to be careful interpreting the data. So, as an example I shall describe the problems with Platycheirus ransarensis.

A bit of history

P. ramsarensis was split from P. clypeatus by Speight & Goeldlin (1990) and Goeldlin et al. (1990). It occurs in oligotrophic (acid, base-poor) situations, most frequently beside moorland streams and lakes, and usually where there are small flushes with abundant sedges or rushes.

When the split was first announced, there was considerable interest amongst the active Dipterists of the day and many went back through their collections to see what they contained. As P. clypeatus was known to be a problem species I suspect many of had a better collection of specimens than we had for easier species. We also took a great interest in looking for this species and our summer field meetings happened to be substantially northern at the time; so lots of records were assembled. There was also considerable activity in the Sorby Natural History Society at the time and they too generated lots of records. Look in the uplands, and it seems that P. ramsarensis is almost a standard species to be expected! More recently, there has been a lot of activity amongst the Devon Fly Group and Dartmoor turns out to be a hot spot. I expect with similar activity both Exmoor and Bodmin Moor will turn out to be other south-western hotspots.

Figure 1. Trend for Platycheirus ramsarensis

Figure 2. Distribution of Platycheirus ransarensis

Interpreting the trend

The overall trend from 1980 says an increase, but I think that would be a misinterpretation. Equally, the trend from 2000 onwards is down, but that too is probably misleading. I think the steep rise prior to 2000 is increased awareness and interest in the Platycheirus splits, whilst in subsequent years there has been a decline in interest in these difficult species that gives an impression that they are occurring less frequently.

In reality we simply don't know what is going on with this one! My field experience suggests that where one looks for it there is a pretty strong chance of finding P. ramsarensis. It is likely to be substantially under-recorded and will probably be found to occur much more widely on the Pennines, in the Lake District, upland Wales, and on the Southern Uplands of Scotland. Further north, I would expect it to be quite widespread across the Western Isles and in the Highlands but probably absent from much of the lower ground of north-east Scotland.

So, will we define a reliable trend? I suspect not unless we start to see an absence from places such as Dartmoor. Whilst the Devon Fly group has many active specialists corroboration of any apparent trend should not be an issue. But, were we to see a decline in specialist activity we might see a negative trend that is a reflection of changing recorder activity rather than a loss of this species.

How might a Malaise trap network work?

In yesterday's post I raised the question of whether we might emulate the German Malaise Trap programme? The ensuing comments were largely positive and several people raised some really great ideas that helped to get me thinking further. So here is a bit of development thinking:

Does it have to be a centralised project?

Probably not; it could be a series of projects that ran independently but then pooled their data as and when the need arose. I think, however, that there would be great benefits to some sort of central oversight and promotion of the project to make people aware of what was going on and what the opportunities might be to get involved.

In the first instance, it would help to have somebody centrally to raise the funds needed to get the project started. At its simplest level, those funds would need to cover the cost of Malaise Traps and preservatives (degraded Alcohol). I think, however, that ther could be opportunities to link up with universities to develop basic identification skills. Even learning how to sort insects to Order would be useful and might help to open a few eyes. As such, maybe there are University Biology Societies that might like to get involved and have a long-term project? So, some resources to equip study centres with requisite microscopes and keys would be a possible draw on resources.

Do traps have to be run for the whole year?

The simple answer is no. What is needed is a programme that runs consistently from year to year. If it is focussed on 'pollinators' that are of commercial interest I think the traps might best be run from the start of May to the end of June. BUT, of course, running traps for only part of the year is only one option and there might be groups who would run traps throughout the year.

Where might traps be run?

The logical place to run such traps is in association with field centres and maybe the head offices of Wildlife Trusts that have a garden or nearby wild area. It seems to me that this is the sort of project that needs to be associated with stable recording locations where it is possible to have one or more people available to operate the trap and to empty the collecting bottle on a regular basis.

How would the samples be sorted?

My initial thinking was that this is the sort of project where one could develop a nice social group that met on a regular/irregular basis to sort samples together and to learn from one-another. It seems to me that the key to any project that needs to run over many years is to make it a social as well as a serious event. It won't appeal to everybody, but providing you can peer down a microscope for a couple of hours, it offers an opportunity to get to meet people and to do something communally.

I quite like the idea of setting up such a project within the regional and national Natural History Societies. In many ways, I think there is a need for societies to develop new relevance to today's world. Events that draw together people of similar interests can be immensely valuable, especially if they include an element of intellectual stimulation that at least a small proportion of society needs: we hear that this is essential to stave off dementia so there is a growing pool of possible participants!

To what level would one sort the specimens?

At its most basic, sorting to Order would at least mean that the insects collected could be investigated by relevant specialists. BUT, when you bear in mind that there are about 80 recording schemes, there is the potential for quite a large volume of material to be identified to species. That is not to say that all scheme organisers would want to participate, but if only 30% did so that would mean quite a large volume of material identified.

Beyond sorting to Order, counts of individual animals might be possible but I think I would desist from this and concentrate on counts at a more refined level – counts of bumblebees, solitary bees, solitary wasps, some Diptera families and some beetles would be a good start. The key is to choose the taxonomic level that is possible with the volunteers available.

Disseminating the results

No long-term project yields immediate results, and the minimum number of years needed to develop a 'trend' is three years! But in reality a ten year span is needed to start to see real changes. Also, one must be realistic that the first couple of years would be a big learning curve and that the data might not be as robust as it would be after the groups had gained skills.

This brings us back to the question of whether a centralised lead is needed? If the data are to be used, they do need rigorous scientific oversight, so some sort of project management is needed. Within that 'management' team one would need both organisers and analysts, so I think it is probably essential that at some point CEH should be involved. Alternatively, perhaps there is a University team who would get involved?

These are just a few initial musings, but as I ponder I think I can see the shape of such a project developing. Now all that is needed is the fire of enthusiasm somewhere to make it happen!

Time to copy the Germans?

Recent publicity about the German Malaise Trap programme and the raw data it has created provides a lot of food for thought!

My last post showed how the UK dataset is highly open to modification by changing recorder practices. We are likely to get a lot more data on a sub-set of our fauna (most welcome), but unless we do something quite urgently we may lose track of a significant proportion of the fauna and end up with a politically weaker situation because the dataset is incomplete and can be chewed up by those vested interests who don't like the messages that the data convey.

I cannot see the UK Government ever funding long-term studies that are highly likely to expose even more weaknesses in their environmental policies, so it is down to the voluntary sector to take action. Could we ever get a network of Malaise Traps set up across the UK? Perhaps it is a long-shot but maybe this article is enough to get a few minds thinking about such a project?

Making it happen

It is one thing running Malaise Traps, and a very different matter if one is going to do something with the specimens collected. They have all got to be stored, and ideally something has to be done with them! Sorting Malaise Traps to Order is a major undertaking in its own right, but it might be possible using volunteers.

Sorting to Family is a rather bigger problem. Might we find volunteers? I don't know, but perhaps it is possible. Finding volunteers to extract particular families might be a possibility?

The logistics are frightening, so I take my hat off to the Germans. For the last couple of years I have been providing Axel Ssymank with a bit of help with proof-reading English abstracts for some of this work. He and his colleagues have done an amazing job and it is great to see some powerful messages emerging. I'd love to see something of a similar nature happening in the UK.

This sort of venture seems to me to require a collaborative project that involves all of the major entomological societies together with the Wildlife Trusts and perhaps others. Could it be pump-primed by a Heritage Lottery Fund project? I can certainly see a possible project, but is there an organisation that might take the lead?

Perhaps this is a step too far for volunteers? BUT, many societies need projects and long-term initiatives to give cohesion to their activities. Could this be one? In some ways, there might be parallels with 'Operation Wallacea' that looked at the fauna of Sulawesi in considerable detail and caused huge excitement at the time.

Any takers?

Interpreting trends in abundance

There is an increasing interest in the trends in the abundance of invertebrates, as illustrated by recent posts about 'pollinators', so it is perhaps apposite that I look at some of the trends in hoverfly abundance and think a bit about the reasons for such trends.

I am starting to get quite concerned at the messages that are emerging and begin to think that we probably need to develop two indices: one based on photographic records, which now make up the bulk of the data arriving at the HRS, and the other based on a small number of individuals who still retain specimens.

My rationale is driven by some startling trends that I don't think can be put down to environmental issues; or, at least, I don't think we can disentangle environmental and recording pressures sufficiently to provide a reliable account.

Here are a few examples extracted from the revised trends that should appear in the updated hoverfly atlas (when it finally emerges):

Neoascia podagrica

This is a relatively common species and we see lots of photographs of Neoascia that are probably N. podagrica, but we cannot be entirely sure from a photograph. What we can say is that it is likely to be either N. podagrica or N. obliqua, and unless there is butterbur Petasites hybridus close-by the chances are that it is N. podagrica. So a question-mark hangs over the data. We can also say that we very rarely see records of Neoascia that don't have infuscated outer cross-veins and yet our own field experience tells us that they are quite widespread and abundant (even super-abundant) in the right places.

Figure 1. Trend for Neoascia podagrica with marked downturn in abundance in the past 5 years.

Melanostoma mellinum

I have always found that this species occurs in lower numbers than M. scalare and it is quite plausible that its numbers have declined somewhat. But the data can be skewed by the numbers of people who record in the uplands where M. mellinum is far more prevalent. We see comparatively few records of this species as photographs, a phenomenon that is possibly complicated by the difficulty of doing Melanostoma from photographs.

Figure 2. Trend for Melanostoma mellinum in which a clear downward trend seems to have intensified in the past 4 years for no obvious reason.

Cheilosia illustrata

This is one of the traditional 'hogweed fauna' and as such might be expected to follow a similar trend to others such as Leucozona glaucia that has declined dramatically in south-east England. Yet, the trend appears to go in completely the opposite direction! My instincts are that because photographic recorders tend to concentrate on larger and more obvious species, this is one of the beneficiaries of such recording.

Figure 3. Trend for Cheilosia illustrata in which the upturn coincides quite closely with the arrival of iSpot and more data extraction from web-based sources.

This trend contrasts strongly with Cheilosia proxima, another member of the 'hogweed fauna' whose larvae are also associated with a very common plant (creeping thistle Circium vulgare).

Figure 4. Trend for Cheilosia proxima.

 

Do differences in recording technique matter?

Dramatic changes in the apparent fortunes of our insect fauna have already elicited sensational (correctly in my view) responses in the press. So we need to be clear about our interpretation of the results. There are parallels: the change in bathymetric readings on some estuaries was quite clear when traditional 'lead lining' was replaced by sonar readings. Without this change being recognised, it was possible that an incorrect geomorphological interpretation would be placed on the change. This in turn might have had important implications for our ports industry.

So, quite simply, yes we do need to think about the ways in which data are gathered and must think about our interpretations. With hoverflies, we are just about getting to the point where the data are so dominated by photographic recording that any change will be followed by a new asymptote, after which we can follow new trend lines. BUT, critically, we need to understand and take the changes into account. Thus, it is unwise to look at trends without undertaking critical evaluation taking into account the factors beyond simple environmental parameters that might affect the animal in question.

My feeling is that for the foreseeable future it will be necessary to develop parallel indicators using two different datasets - one based on traditional recording from retained specimens and the other from the photographic record. I suspect there is an element of inevitability that the photographic record will start to become the dominant indicator; in which case we need to be aware that trends for difficult taxa may not be wholly reliable and thus conservation organisations will need to develop new ways of thinking about species' status and conservation policy.