Sunday, 22 October 2017

Do we understand pollinator abundance and population trends?

Dave Goulson's recent editorial in British Wildlife raises an important point about the issue of pollinator abundance. His analysis does, however, overlook the fact that there are active data collection processes for the most obvious pollinators. Existing datasets compiled by the Hoverfly Recording Scheme and BWARS are regularly used by CEH and various university groups to produce new analyses and in the development of new analytical techniques. So, everybody who posts on the UK Hoverflies Facebook page is contributing to the research. Nevertheless, he is certainly right in saying that there is a lack of data for many families of flies and for some other insect Orders.

In broad terms, we have a very good understanding of what is happening to our hoverfly fauna - somewhere in the order of 40 to 50% is declining and perhaps 15-20% is increasing. We see an expansion in the range and abundance of southern thermophilic species such as Volucella zonaria and V. inanis and Rhingia rostrata. Declines are highly apparent among those species that favour damper conditions. I think we are starting to see the loss of some species from south-east England. For example, the spectacular blue-marked Leucozona glaucia seems to have substantially disappeared from much of south-east England in the past 20 years.

Techniques used in analysis of trends have evolved, and new occupancy models are emerging on a relatively regular basis. They are all dependent upon a continuing stream of data, which makes it imperative that BWARS and the HRS remain active and train new recorders. Perhaps even more critically, we need to develop succession plans to make sure that the process of data assembly and dissemination continues; it is a very labour-intensive  and is starting to become more of a challenge as the numbers of active recorders grow. Nevertheless, this challenge is, in effect, a good news story because it shows that there is positive progress in data assembly.

BUT, are hoverflies really important pollinators?

What are we actually talking about when it comes to pollinators? Politically, the main focus will be on pollinators of commercial crops, many of which flower early in the spring. Thus, a decline in species that fly after critical crop pollination time may be of little commercial interest and therefore equally of little political concern. I am not sure we have really made that distinction yet, but if one was to do so it might help to focus attention on other parts of the insect assemblage such as Anthomyids, Muscids and Calliphorids; or perhaps even Bibionids that occur in vast numbers for very short periods of time?

We do have other proxies for insect abundance. For example, the numbers of insectiverous birds. These too are substantially declining. Why? Well some of the reason lies in general agricultural intensification and loss of wild places in the countryside matrix. Partly it may be associated with the development of vast monocultures and the apparent focus on the same crops in the same fields year after year. A reliance upon pesticides is a likely further factor that diminishes the food supply at critical times of year.

But there are other factors too. For example, there is a developing trend for insects to emerge earlier in the year during a brief warm spell in late March and early April, before a cold snap in late April and May knocks them down. This sort of seasonal change seems to me to be having a profound impact on insect populations. Equally, we quite frequently get short bursts of intense heat in late June and early July, which probably knock out larval stages. I suspect drought and heat stress are a very important factor behind changing insect abundance in south-east England. Warm, damp summers are always looked upon by the public as undesirable, but regular rainfall is probably the single most important factor behind the maintenance of insect populations in Britain. If anything, we are seeing greater stability in insect numbers in northern and western areas - this certainly seems to be the case for hoverflies.

Do we need better monitoring?

Of course the simple answer is yes! But we also need to be clear about the objectives of monitoring and the degree to which we try to link monitoring results to politically sensitive issues rather than to a broad spectrum of ecological factors. Should monitoring focus on species that are potentially important commercially, or should we be looking across a wider spectrum? If so, will the same monitoring systems deliver the results needed for each purpose? Or, can we use proxies - a general pollinator monitoring scheme that assumes that the trends are the same in different families of bees and Diptera?

Looking at the issue of monitoring from a purely practical perspective, I think the current use of datasets compiled by the HRS and BWARS is probably the most viable option in the long-term. Government-funded packages might generate data collected in a more consistent fashion, but it is always going to be vulnerable to cuts. We have already seen this with the long-term data for Atlantic plankton and in the Rothampstead moth trap programme; both of which generate immensely important and instructive messages; unfortunately the messages are not all positive and they don't generate the steady stream of high impact papers that keep research funding flowing. So, voluntary data collection remains the only reliable source of information on trends. That makes it imperative that the core functions of the Biological Records Centre at Walligford are safeguarded.

So, what can you do to help?

There are several aspects to monitoring:

  • Range and distribution: what occurs and where does it occur?
  • Abundance: in what numbers do individual species occur?
  • Variation: how do numbers of species and absolute numbers change regionally and nationally over individual years and in longer-term units?

At the moment, we have a relatively small number of people who regularly record from their garden or wildlife area. There are several very committed members of the UK Hoverflies Facebook group who record on a daily basis. More of this sort of recording is likely to be helpful because it may be possible to take sub-sections of data for analysis if we have more such datasets. Occasional ad-hoc records are also useful because they help to fill in gaps in distribution data. Occupancy models depend upon good general coverage, so even a few common species recorded from a location can make a difference; this is particularly important in places where there are limited numbers of active recorders or that people don't regularly visit.

Friday, 20 October 2017

Dipterists Forum Autumn Field Meeting - Farnborough and district

In addition to the week-long trip we had at Loch Lomond in September, There was a 'spur of the moment' trip to the Surrey/Hampshire borders by a small group of die-hards who find it difficult to hang up the net and pooter for the year. In the past there has been a four or five-day meeting around the third week in October and a few of us wanted a bit more field work before winter sets in. Thus, I booked three rooms in the Travelodge in Farnborough for Peter Chandler, Alan Stubbs and myself; Andrew Halstead, Tony Davis and Mark Mitchell joined us for all or part of the time, travelling from home.

Most of the sites we looked at were in north Hampshire (many thanks to Tony Davis for organising access permission), although Alan, Mark and I did take a look at the area around Shere and the Winterfold Forest in Surrey on the Saturday.
Mark Mitchell demonstrates the newest technique for extracting flies from a pooter - centrefugal force to stun them and send them to the end of the pooter with Peter Chandler looking on in amazement!

The trip was relatively uneventful and we have still to get the results from the samples of fungus gnats that were gathered. My impression was that there were plenty of gnats, but that range and variation was limited. I saw precious few Boletophila or Macrocera and it seemed to me that the majority of specimens were from within the Mycetophilidae. Maybe the results will differ, as there were at least four of our party collecting gnats and there should be a very big selection to choose from. If we are lucky, we might have managed to find somewhere around 130  species but I think I might be a bit over-optimistic in that estimate.

Craneflies were incredibly sparse in both numbers and species diversity. I would be amazed if we managed to find 30 species over the four-day trip! On the plus side, I cannot recall ever seeing so many Heleomyzids but even this assemblage was odd: the bulk of my samples were Suillia with just the occasional Tephrochlamys. Drosophilids were fairly abundant (especially D. suzukii) but Platypezids were also noteworthy by their absence.
Alan Stubbs, Tony Davis and Andrew Halstead deliberating over the choice of next site
Although perhaps not the most rewarding meeting from a recording perspective, we did manage to visit nearly 20 localities and covered an area that has not previously been investigated by an Autumn field meeting.

In addition we experienced the most odd weather at Greywell Moor where light intensity eerily dropped to dusk-like levels around 2pm as the edge of Hurricane Ophelia drifted past on Monday the 16th. One could almost imagine that this was the start of the Martian Invasion and would have made an amazing backdrop for a rendition of Jeff Wayne's 'War of the Worlds' (the Richard Burton version) ---- and it was not that far away from Horsell Common either!

Thursday, 19 October 2017

Mitcham Common survey - A reflection

From August 1983 to September 1984 I led a team of six recent graduates employed to conduct an 'Ecological Survey' of Mitcham Common. It was funded under the Manpower Services Commission's 'Community Programme'. The timing was far from ideal because most of the time was Autumn and Winter, whilst by July we were stuck into writing our report. Nevertheless, we managed a great deal and produced a useful report. Looking back, I certainly learned a great deal from the project, and I know that at least one other team member benefitted from the experience and went on to a career as an ecologist.

But, I hear you ask, 'were the results reliable and trustworthy?' Well, they were as good as we might hope to achieve. Where possible, we sought expert advice to validate our diagnoses, and I am pretty sure that most of the results were reliable; even if there were misidentifications in places. At the time, I felt the biggest problem area was the macro-fungi; this remains my biggest concern in terms of diagnostics. Today, I have greater misgivings about some of the recommendations that were made. In hindsight I (as team leader and editor) lacked the experience to make some of the judgments I would have made today. Hindsight is a wonderful thing!

There were about 60 copies of our report; most of which went to the Board of Conservators and to the London Borough of Merton. Two went to the then Nature Conservancy Council and one to the London Ecology Unit but I cannot recall any others going anywhere useful. How many survive? Very few, I suspect, and of those most will be in inaccessible personal libraries or filing systems. I expect many will have been pulped!

Fortunately, I do have a couple of copies and last year I decided that it was a lamentable waste of public resources to have the report but not to have it in an accessible form. I therefore OCRd the whole report (nearly 300 pages of tables, diagrams, maps and text). The OCR process and scanned illustrations required a lot of work to turn them into a decent machine-readable version, so in the end I re-typed many of the tables and re-drew the graphs. Sadly I did not have the original raw data so some of the graphs are best estimates based on the originals. Nevertheless, the whole package is now available in machine-readable form. I have sent it to the Warden so he has a copy, and hopefully it will be made available to a wider audience; not that it is thrilling reading, but it is a valuable baseline.

Future thinking

In my view, Mitcham Common is one of the most important wildlife sites in south London and therefore it is important to make sure that there is a permanent archive of relevant science. There is a very old paper on the birds by my father (sadly his diaries were lost when Mum cleared his effects) and of course there are papers by Louseley and Saunders on the botany. Since 1984 I have published accounts of the aculeate Hymenoptera and some aspects of the Diptera, but there is a lot that has yet to be studied or reported. I have a good many more Diptera records now, so maybe I will write another account. That leaves an awful lot more to do.

The 1984 team barely scraped the surface of the Coleoptera and Arachnida, whilst I dare say a lot more could be made of the Lepidoptera (I know David Lees did a lot on micro-leps in the early 1990s but I guess his report has been lost).

Looking at the 1984 report, I lament the lack of foresight on my part. I should have created a photographic library of the site; it has changed immensely and having detail would help to put some context into the changes in both the animal and plant components. I also wish that I had been more diligent in collecting Diptera from 1984 onwards – I am sure the fauna has changed markedly as the site has dried out very substantially.

So, the big question is 'can anything be done to create a new baseline?' I don't feel equipped to take on the full panoply of taxa and my botany is too rusty to re-do that part of the study. I do wonder, however, whether there is scope to gather together a group of local specialists to re-survey the site and to try to fill in some of the gaps using modern techniques? If there was interest amongst local Coleopterists, Arachnologists, Mycologists etc. then perhaps a new project could be developed, perhaps providing training to a new generation of aspiring specialists. What is needed is a vision to provide focus, some leadership and willing volunteers: any takers? At the moment I am able to offer time and enthusiasm, but I would not do so unless there is a group that would also be willing to participate.

Thursday, 12 October 2017

An opportunity to improve our knowledge of Diptera

The fungus season is with us, and yet again I find myself thinking that I really must start to try to breed flies out of fungi. Each year I fail to do so; mainly because I am not confident that I can reliably identify the fungi concerned. This year is no different! There are lots of Russula and other species to choose. So perhaps I will have another go!

What do you need to do?

If you find a fungus with larvae in it, retain it in an open container - do not place in a plastic bag as CO2 will build up and kill the larvae.  When you get it home, place it on top of some sterilised coir (heated and dried in the oven to kill existing larvae) or similar material that will soak up the decayed fungus and provide a pupation site for the larvae. Cover the container with a fine gauze and place in a position where you are likely to regularly inspect it.

In due course, fungus gnats and other fungus-feeding flies (e.g. Platypezidae, Helomyzidae and Drosophilidae) should emerge. These can be removed from the container and stored for later identification. If you don't have access to ethyl acetate, which is the normal killing agent used by entomologists, then the freezer works just as well.

Keep a record of where your fungus was found, what species it was (if not to species then to genus) and when the flies emerged from it. Later in the winter these flies can be passed on to the fungus gnat recording scheme and will help to fill in gaps on the maps but, more importantly, they might add useful ecological information on the host fungi used by different species.


Try watching fungi for the flies that visit them, and then catch the flies up for passing on to the recording scheme (care needed not to inhale fungal spores if you use a pooter). Armillaria is especially good and can yield a lot of species if one takes a diligent approach to watching and collecting.

The majority of fungus gnats require dissection and cannot be identified from photography, but there is an exception in the Platypezidae, some of which can be identified from photographs.

Friday, 29 September 2017

Tackling Diptera families – where to start and how to progress

In Britain, the fly fauna now comprises around 7,100 species. The number has risen dramatically in the last twenty years, by around 350 species. It is currently the largest single component of our fauna but may eventually be surpassed by the Hymenoptera if the taxonomy of the Parasitica is ever resolved!

The sheer numbers give us a lot of headaches. Can one individual really tackle them all? If you cast around it is clear that even the most competent Dipterists tend to specialise.

The big question is how to get started and how to progress from there onwards? The trouble starts with finding a reliable key to families; we don't have a published key that is simple. 

Life gets complicated because there are now two systems for naming the parts: for example the Comstock-Needham system of naming the wing veins, which has been around for a century or more, and McAlpine which is more recent. Older Royal Entomological Society keys use the former and later ones tend towards the latter. So, when you start with Diptera there is an added level of confusion with two completely different sets of anatomical names! We do make life difficult for ourselves!

Most Dipterists dislike the AIDGAP key by Unwin, and there is agreement amongst the leading specialists that it does not work in some places. The best readily available key to families is Pjotr Oosterbroek's key to European families of Diptera but it is not for the faint-hearted. There are many technical terms and unless you are familiar with, for example, the nomenclature of wing veins, it is often hard work switching back and forth from key to illustrations.

Stuart Ball and John Ismay have been working on a key that deals with the British fauna. It is now pretty well developed, but cannot be published because it relies very heavily of illustrations cribbed from other publications. Stuart is in the process of photographing all of the relevant features so something may emerge eventually.

So, where to start?

Most people tend to start by noticing animals that are obvious. Leaf-baskers and flower visitors. They naturally gravitate towards families such as the Syrphidae for this reason. But it is not just Syrphids that visit flowers: lots of Calyperates do too, especially Tachinidae, Calliphoridae and Muscidae. Unfortunately, user-friendly modern keys are not available for all of these families and modern entomologists are somewhat spoiled by the keys to Syrphids. Stubbs & Falk does an amazing job of turning a family that was once considered too hard for all but the museum specialist into one that can be tackled with relative ease. [I do stress relative ease – parts of this family are far from straightforward!]

The big advantage of Syrphids is that once you have learned what they look like, you have also been introduced to quite a few non-Syrphids and a certain amount of comparative anatomy – not a hoverfly but what is it? If it has bristles then a lot of people are rapidly turned off because the keys rely on the relative positions of the bristles or bristle scars. Nevertheless, once you have mastered hoverflies you may want bigger challenges. Soldierflies and their allies sit comfortably with hoverflies so they too get tackled quite early on. Thereafter, it is a question of whether there are accessible keys but, perhaps more importantly, also whether you can actually use the key and have some confidence that the point you arrive at is reliable.

In my early days running ecological surveys I had some interesting discussions with colleagues who took the view that the end point they had reached was always right – whereas I felt that one should check further and remain cautious. If there is a species description, read it! If the description says that your species is confined to the far north of Scotland and you have recorded it in Dorset you are as likely as not wrong! We see an awful lot of duff data that can be eliminated quite quickly because the geography is wrong.

Moving on

In my early days as a Dipterist, there was a lot of interest in hoverflies because Stubbs & Falk had just been published and even the seasoned 'experts' were breaking new ground. Over time, those people have moved on from hoverflies and into other families. The challenge is breaking new ground and finding species you've not seen before – it is a sort of 'collector' approach that is utterly understandable: unless you are interested in some form of data interpretation the greatest thrill is something new.

Today, many of those former hoverfly enthusiasts tackle other families and only take a passing interest in hovers. But, they do this as a progression: there is a moderately workable key to Dolichopodids and they are quite attractive flies; Male Empis and Rhamphomyia, with their exhuberant genitalia, are also interesting and Collin's key is very workable (in parts); there is a reliable key to Sciomyzidae and they are eminently doable; the Tephritidae are pretty doable (but I do have trouble in places), as are Conopids, Otitidae and Uliidae.

Thereafter one starts to enter a minefield. There are keys to Phorids, but I would not touch them (very few Dipterists will) – they require slide mounting, as do Psychodidae. Likewise very few people tackle Sciarids or Sphaeroceridae. More importantly, when starting with a new family you really don't have the markers that help you find your way around the key. If you have access to a reliably determined collection then you can get to grips with a new family; if not, how do you know whether you have got the right ID? Your fly is pink with blue spots, but all the key does is to tell you that it has two notopleural bristles and crossed post-ocellars! You are none-the-wiser!

Where the keys are sparsely illustrated and lack species descriptions  potentially doable families are as yet under-attempted. The Tachinidae are a case in question. They are often big and seemingly obvious, but try using the key! Unfortunately there are a lot of single species genera that make the key a long procession that becomes very confusing. I've yet to master it but have this on my to-do list for the winter! I've been collecting Tachinids all year and now have three or four hundred to tackle. Hopefully that will get me further!

Tackling a new family

It is not really viable to tackle a key with just a single specimen or indeed a handful of specimens. Within moderately large families you just don't have the comparative material needed to understand what the key is talking about and even some small families can be a problem without relevant comparative material.

The system a lot of the more adventurous Dipterists use is to collect for a couple of seasons before attempting to get to grips with the key. When I do this, I attempt specimen one and see how I get on? If I hit a block then I put it to one side and try another, and another and another. Each time I familiarise myself with another facet of the key and start to see how it is constructed and how the writer has interpreted the morphology. Over time come a few small successes: those start to be the markers in the key – I know what that is and the next specimen is not it! We try to do the same when running training courses – make sure that critical parts of the key are embedded and the student has some simple markers to work from.

Crucially, this all takes time. Finding your way around the families, recognising features such as costal wing breaks and head chaetotaxy requires infinite patience and access to comparative material. So, the follow-up is a need to maintain a collection. That in turn becomes the limiting factor – store boxes and cabinets are expensive, take up a lot of space and require curation, so in the end you have to specialise!

Wednesday, 27 September 2017

Making envelopes for papering gnats and craneflies

If you are minded to collect either (or both) craneflies or fungus gnats for Alan Stubbs and Peter Chandler, it is simple enough to store them in advance of sending them off. Making the storage system is described in six simple steps.

1. Cur a square of paper about 7cm square (or thereabouts). I usually fold over an a4 sheet into two and then two again - this gives me potential for 12 squares. Alternatively, you could use old postage envelopes and simply cut off the corners to appropriate sizes.

Figure 1. Basic square of paper
  2. Fold the square into two to make a triangle
Figure 2. Folded into two to make a triangle - in this case the square was slightly rectangular but that does not matter.
3. Turn over one open side of the triangle to seal it. I usually don't worry about using tape to make sure it stays closed but you can if you feel so inclined.
Figure 3. One side of the triangle sealed by folding over.
4. Write relevant data on the triangle BEFORE filling it with specimens otherwise you will crush them.
Figure 4. Triangle with data - I usually smaple both gnats and craneflies so I need to put a note as to what the envelope contains.

5. Fill the envelope with sorted specimens - you should be able to open the envelope by putting pressure on two sides to cause the remaining open side to part open. However, to show what the envelope contains I have opened one to show how the flies are arranged.
Figure 5. Triangular envelope containing fungus gnats.
6. Seal the open side by turning over and making sure there is a good fold.
Figure 6. Sealed envelop ready for storage.
It is probably best to liaise with Peter and/or Alan before sending large volumes of specimens, but both of them are usually pleased to get specimens that will improve coverage by their schemes.

Scottish square-bashing: an update

When I went to Scotland in June, I made a serious effort to record craneflies and fungus gnats in addition to hoverflies. Wherever there was suitable habitat for these families, and it coincided with a potential recording site for hovers, I swept around for a little while. On most occasions my efforts were quite limited, but occasionally I spent a reasonable time sweeping because the weather was not conducive to recording hoverflies.

I've just had a summary of the fungus gnat results back from Peter Chandler. It transpires that I managed 221 species/site records from 30 sites comprising a total of 94 species (about 17% of the British fauna). Unfortunately, my timing was not ideal and I was probably a little early in the year but I did get a few whose distribution is mainly Scottish. The best site list I generated was at Craigellachie where I managed to find 42 species which is almost a respectable total!

Possibly the best record I generated was Ditomyia fasciata from a site near Barnard Castle in Co. Durham (see map of records up to 2011). Apparently I also took a specimen of this species in Wingate Plantation during my visit to John Bridges in June. These two records are clear northward extensions of its known range. Maybe it is responding to climate change but, then again, coverage is not fantastic in NE England (although we did have a summer field meeting based in Durham in 2005).

Figure 1. Distribution of the fungus gnat Ditomyia fasciata to 2011
Peter tells me that fungus gnat recording has been very limited this year – our spring field meeting generated a few records and the Summer field meeting generated about as many records as I generated in Scotland, but with about 30% fewer species (one set of specimens still to be processed may change things).

This feedback is very useful because it highlights just how important parataxonomists such as me could be to this recording scheme. Peter lives in southern England and will never manage to cover the country on his own. So a combination of field meetings and individual efforts is needed to improve coverage. So, do you own a net and a microscope (and pooter)? If so, it is not too late to start collecting fungus gnats and supplying them to Peter.

I’m now hard at work sampling Mitcham Common for its gnat fauna. It is darned hard work as there do not seem to be many gnats about. Perhaps it is the season; but, then again, the site supports relatively young woodland and is infested with bramble so it may just be that it is not a good gnat site. Time will tell.