Saturday, 18 November 2017

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.

Wednesday, 15 November 2017

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!

Tuesday, 14 November 2017

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.

Monday, 13 November 2017

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.

Sunday, 12 November 2017

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!

Saturday, 11 November 2017

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.

Friday, 10 November 2017

How many records in the database are unreliable?

I am currently working my way through the latest maps and histograms prepared for an updated atlas. It is a very slow process because so many of the species accounts require changing in the light of recent data. However, there are some consistent problems and one or two that give rise to uncertainty about the data. So, here are a few examples:

Eristalis rupium

This is mainly an upland species that does occur in lower-lying areas in Scotland. In this case there is an obvious doubtful record from Norfolk. This record comes from the NBN and thus has not been previouslyassessed or checked by us. This is a fairly common problem and we should be able to fix it. If there is a specimen or photograph and we can examine it we can test the veracity of the record. If there is no means of corroboration we will mark as 'requires confirmation' and it will not appear on the maps. Likewise, there is a record from around Hull that requires further investigation - I suspect this too is wrong and that somehow it has slipped through the net of basic checking when we import data.
Figure 1. Distribution of Eristalis rupium in un-filtered data. Record for the Norfolk coast seems highly implausible.

Melangyna quadrimaculata

This is a very early spring species that is quite difficult to identify and might be mistaken for a Cheilosia in the variabilis group. Also, recent experience has shown that dark specimens of Leucozona laternaria are sometimes run to this species. So, the phenology histogram needs to be treated with care: are later records of larvae or adults? If the latter then the chances are that the determination is incorrect and, again unless there is a way of corroborating the data the records will have to be marked as 'requires verification'.
Figure 2. Phenology plot for Melangyna quadrimaculata with outliers in July and August that are almost certainly misidentifications

Melanogaster aerosa

The last two examples are really quite simple, but there are many more complicated ones where there is uncertainty. The data may be right, but they are likely to be badly wrong. This is exemplified by the histogram for Melanogaster aerosa which is fiendishly difficult to separate from M. hirtella. As far as I know, I have never seen it, despite checking many thousands of Melanogaster! I can be certain I've not seen the female, but males are a bit more problematic. Thus, what can be made of the phenology histogram? Alan Stubbs reported in his monograph that M. aerosa (Figure 3) tends to occur later in the year than M. hirtella (Figure 4), and yet we see a substantial overlap and almost two generations, one in April/May and the other in July and August. I suspect a substantial level of mis-identification. The big question is 'how to resolve this one'? I think we are going to have to look very carefully at who the records come from and probably to exclude data from all but those who we have a reasonable knowledge of their ability. This sounds a bit harsh, but clearly there is something adrift with the data here. There are a number of other species where we will have to look equally carefully.

Figure 3. Phenology histogram for Melanogaster aerosa
Figure 4. Phenology plot for Melanogaster hirtella
Platycheirus immarginatus

In our experience, this is a strictly coastal species and there is confusion between females of this species and females of P. perpallidus. So the likely approach is to produce a map based solely upon records of males by known reliable recorders.

Figure 5. Distribution map for Platycheirus immarginatus based on raw data.

Friday, 27 October 2017

What can we do to increase the numbers of hoverflies?

My last post elicited some interesting and challenging comments on the UK Hoverflies Facebook page so it is time to start to think about what we can all do to help improve the numbers of hoverflies. To do this, I think we should start with what what the larval stages need rather than the adults require. Adults are simply the breeding and dispersal stage; whereas the larvae are the critical bit of the cycle. If there is no suitable larval habitat there won't be any hoverflies apart from those that are tourists from suitable sites.

We can break hoverfly biology into a series of guilds:
  • Predators (on)
    • Aphids
    • Other fly larvae
    • Lepidoptera larvae
    • Coleoptera larvae
  • Saprophages (dwelling in/feeding on)
    • Rotting plant matter (including dung)
    • Decaying sap
    • Rotting wood (or more precisely fungal hyphae in rotting wood)
    • Fungal fruiting bodies
  • Aquatic filter-feeders feeding within
    • Shallow parts of large water-bodies
    • Small pools
    • Water-filled rot holes
  • Within plants'
    • Leaf and stem miners
    • Root and rhizome dwellers
The above is quite a simplification but it will suffice for this analysis. We also need to think about the duration of the life-cycle. Some species have multiple generations each year and their numbers can fluctuate markedly within and between years (often the colourful Syrphus and Eupeodes, the small but very abundant Melanostoma and Platycheirus, and the bee-like Eristalis that make up a big proportion of the numbers we see). Many others have a single generation each year; and a few take several years to go through to maturity (mainly those associated with decaying heartwood such as Callicera rufa and Blera fallax).

And, finally, we need to think about the durability of the food supply: does it fluctuate in volume over short periods of time or is it comparatively constant providing there are no stochastic events to interrupt availability? If food supply is constsistant then the animals probably don't have to move far and, once a new food source has been established, numbers of relevant hoverflies should increase. If the food supply is prone to fluctuation, the numbers of associated hoverflies are also likely to wax and wane. So, when we look at hoverfly abundance we can tell quite a lot about the consistency of food supply.

The more specialised the hoverfly, the greater the likelihood that its numbers will be comparatively low. For example, species that breed in decaying sap under bark will only be able to do so for a short period whilst the sap is available and may occur in high numbers at a small site for a short time; after which they must disperse to find new breeding sites.

Design of measures to enhance numbers

If we want to increase the numbers of 'pollinators' we need to think about which are the main pollinating species and whether we are talking about crop pollinators or pollinators of wild flowers?

For crop pollinators, my impression is that the bulk of these are species that breed up in large numbers over short periods of time – Eristalis, Eupeodes, Melanostoma, some Platycheirus, and Syrphus, and are numerous in the spring. Many more species will play their part in the pollination of wild plants with some being potentially important e.g. Cheilosia bergenstammi gets covered with ragwort and dandelion pollen.

So from a crop pollination perspective, filling in those field boundary ditches probably eliminated your Eristalis and the removal of the hedgerow and associated leaf litter will have eliminated first generation Melanostoma and Platycheirus. The loss of tall herbs such as hogweed and angelica in the hedgerow will have eliminated many Syrphus, Eupeodes and Melangyna. The same holds in our gardens – raking up all the leaves and burning them or composting them will remove over-wintering larvae of the afore-mentioned and, if you have fruit trees, you will be loosing your Epistrophe eligans larvae (which can be very abundant on plums in particular).

A more comprehensive strategy is needed to cover the wider spectrum of species that inhabit unusual or specialised habitats. For example, that single gnarled ash, sycamore, horse chestnut or beech in the hedgerow will provide wet rot holes for specialist filter-feeders and rotting heartwood for specialist saprophages such as Criorhina sp., Mallota cimbiciformis, Myolepta dubia and Xylota segnis. This also applies to our parks and town trees: cutting down the character trees is destructive, but then employing the stump grinder adds insult to injury by eliminating a potential 20-year food supply for the rotting root dwellers.

To many people, a field edge full of creeping thistle might be a major problem, but for some hoverflies they are bliss – Cheilosia proxima for example will be busy mining the stems. Likewise the wet field with marsh thistle may provide breeding grounds for Cheilosia albipila, C. fraterna and C. grossa.

Small-scale and landscape scale

Within the urban environment we can do a lot by creating small pools, log piles, litter piles or by not over-tidying leaves in the autumn. Our local authorities can stop using stump griders and could place felled trunks in semi-shaded places where they can be felt to gradually rot away (avoid intense sunlight as this dessicates the timber too quickly and creates a hostile environment for saproxylic flies (but some beetles like this sort of timber). Big timber with thick bark is especially valuable as the sap under the bark is protected for a couple of years and this allows the flies time to go through several life cycles.

Within the wider landscape, we need to think about the inter-connectivity of micro-habitats: field margins, ditches, hedgerows and hedgerow trees. Re-wildling is a great idea but is really rather impractical in most areas where we now have arable prairies. Nevertheless, creation of new networks of hedgerows, ditches small ponds and coverts would go a long way to make up the deficit. But, don't forget the specialist features too! For example, seepage lines are immensely important for a wide range of wetland Diptera, including many Platycheirus, Chrysogater and Melanogaster. Set those areas aside as wild places – they are often poor yielding anyway, as are the boggy low-lying areas near water-courses. And in sheep country – reduce grazing pressure on seepage lines so that there is decent vegetation structure rather than a short turf that quickly dessicates on a hot day.

Soil conservation

We hear a lot about 'special sites', but what makes them special? To my mind, the critical issue is that they have not been cultivated for a long time (rarely never) and therefore the soil structure is more suited to maintaining a rich and varied vegetation. We have long-overlooked soil mycology and bacteriology as important conservation features. If the mycology is right you are far more likely to get the hoped-for vegetation. Safeguarding what we have is essential, whereas creation of new habitat on former arable land, that has been sterilised by years of deep-ploughing, fertiliser application and use of pesticides, is always going to be less successful in the short- to medium-term and possibly also way beyond that. 

If, however, all you have is sterilised soil  you must work with what you have and be grateful for what arrives and thrives. But, by thinking about micro-habitat you might just create something that stands a better chance of creating the breeding grounds for hoverflies and other Diptera that are one part of the pollinator assemblage. Measures for solitary and social bees differ somewhat but simply involve the adoption of a multi-layered approach to habitat design.

Thursday, 26 October 2017

The moth snowstorm and insect decline

Having just listened to Adam Rutherford's piece on insect decline on Radio 4 tonight I was reminded of my early days as a moth enthusiast. One night in around 1983/4, the late Steve Church (who founded Bioscan UK) and I went to Salcey Forest. We arrived after dark as Steve was never very reliable with his time-keeping! But, perhaps that was fortunate because I well remember the absolute blizzard of moths in the headlights that night! Equally, I am reminded of the wonderful flight of the Ghost Swift moths along the edge of Mitcham Common in July those days. I don't remember when I last saw a Ghost Swift, let alone dozens bobbing around in the gloom.

But, again, I heard a bit of under-play of current levels of recording from Dave Goulson, who commented that we have good data for butterflies and moths, and less reliable data for bees. I do wish that a bit more attention was paid to what actually goes on - we don't lack biological recording but we do lack the tightly regulated monitoring that might be achieved by an expensive long-term study. So, do I detect a bit of propaganda here? I am reminded of a meeting with another academic group that was proposing to seek a research grant to investigate the distribution of Horseflies in the UK who had not even heard of the relevant recording scheme that had been running for way over 30 years!

To be fair to Dave Goulson, he did mention that there were data for bees, but he might also have mentioned that there are around 80 long-term voluntary data collection programmes for Britain's biodiversity and that the UK pretty well leads the World in the use of non-vocational data collection. Despite this, we don't have the data that the German 'Amateur' entomologists have gathered (I hate the term 'Amateur'); but just take a look at the volume of data on GBIF and you will find that for almost all taxa the UK is a bright red mass when compared to the rest of Europe, let alone any other parts of the World. Those data are actually pretty powerful for quite a wide range of invertebrates and have been used in many studies that have identified equally worrying trends in invertebrate abundance.

And, sorry to say Dave, if the data for bees are ok but limited, those for hoverflies are probably rather more robust! As I recall the HRS and BWARS hold roughly similar datasets in terms of numbers of records, but whereas BWARS covers perhaps 550 species, the HRS covers 283 species! We now hold well over a million records (but with some duplication). So lets see some acknowledgement of those other schemes that regularly provide good quality data for academics and Governments to make use of; and we do it all for nothing!

A more critical message

I will, however, concede that we and others could have made a lot more noise about the issues of insect declines and that the German data do tell a particularly important story that does not get picked up in UK data. The big point that the German data tell us is the absolute biomass change and that is critical. Sadly, UK recording schemes don't give us this sort of result and it is of massive importance.

Declines in individual species using occupancy models mask the scale of decline that is potentially happening: if they rely on presence/absence, then one record for a 1km or 10km square is equally significant and does not change the model. So, somehow, the next generation of models needs to take account of absolute numbers of records. Add to that, we desperately need to see far more reliable day-to-day recording so that changes in the relative frequency of individual species can be detected. I have previously used the case of the Passenger Pigeon and perhaps there are analogous species in the insect World that are heading in the same direction? Just because it is common does not mean that it is not worthy of recording!

Do we need more funding?

It would be easy to say yes, but I think we have got other work to do that does not involve funding. It requires the recording schemes to make a concerted effort to break the community of natural historians away from a fixation on rarity and upon dots on maps; both of which are a problem if one wants to get a decent dataset that tells us something about overall population changes.

So, as a first step, let us see more recorders making daily counts of the animals that they see. Please try to note full lists for each day rather than just the highlights. For me, this is the great benefit of BirdTrack and as such I want to see the HRS move in the same direction. We really need a network of recorders who record all species on as many days of the year as possible.

Similarly, we also need to generate a much bigger base of people who can identify the full range of species, or who are prepared to retain specimens for technical specialists to analyse. For me, the recent publicity on insect decline highlights the importance of reliable data collection and the importance of whole assemblage data. It shows how the 'take nothing but photographs, leave nothing but footprints' approach leaves conservation science weakened so that we cannot provide the robust messages that the German dataset has provided: full marks to our German counterparts!

Now all we have to do is to move the goalposts and start hitting those targets: that means we need more competent invertebrate taxonomists, which in turn means that there need to be incentives for people to invest the many years that it takes to become taxonomically competent. Perhaps at last we are starting to realise that if you cut soft targets, they start to become a weakness in the system many years later that cannot be rectified just by throwing cash around!

Take photos and retain specimens - best of both worlds?

I have previously written about the way John Bridges has greatly increased his site lists by retaining specimens that he passes on to me for ID. There are a few others who do the same. Yesterday I worked through a batch of specimens collected by Martyn Hnatiuk who is based in South Wales. That was highly instructive and useful because Martyn managed to collect several species that are very rarely recorded and would not have been identified from photographs. Three stand out above the rest:

Cheilosia carbonaria - a species that is regarded as 'Nationally Scarce' and which I have not seen in ten years! This specimen confused me a great deal because the antennae were quite strongly orange but the wings were smoky. At first I wondered whether it was a new species but upon checking Van Veen it ran very easily to C. carbonaria. This is an object lesson in the need for care when using what seem to be reliable characters. In Stubbs & Falk, C. carbonaria sits in a group of species with dark antennae and this specimen refused to go that way. So, we would never have achieved a reliable result from a photo and using Stubbs & Falk. It shows that there are always the exceptions that prove the rule!

Eupeodes nitens -  I have only seen this one a couple of times, several decades ago, and there are very few reliable recent records! Again, it did not wholly follow the key in Stubbs & Falk, but readily dropped out using Van Veen. This one would never have been done from a photo because the critical diagnostic characters are on the sternites of the abdomen.

Trichopsomyia flavitarsis - a species that is closely associated with very acid sites and which we very rarely get records of. At one time I used to see it pretty well whenever I went to the north-west (or at least that is my memory) but I've not encountered it for a very long while so it caused me quite a lot of confusion at first.

So, I wonder what else is out there that more recording might turn up? Martyn got a fair selection of  species that we would not have managed to ID from photographs, thus greatly improving the resolution of his data. John Bridges has done much the same. Perhaps others would like to do something similar?

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 they are 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.