Post field meeting reflections

This year's Autumn field meeting was far less productive than previous recent years. Unlike 2011, when we recorded over 200 species of fungus gnats, gnats were very scarce and we barely scraped past the 100 mark. Conversely, craneflies were a bit more abundant and we managed 58 species which is substantially up on recent years but still nowhere as good as lists for two decades ago. What has caused the change?

Forum members Andrew Halstead, John Bratton and Malcolm Smart

at Newborough Warren

The key point I think is that we visited many very suitable sites but the weather was much colder than in previous years. Many sites were west-facing and took most of the day to warm up, and by the time they were getting any sunshine the heat had gone out of the day. However, we cannot dismiss the effects of a very wet year which has had a detrimental impact on much of our insect fauna. Species that favour wet environments do seem to have fared better than in previous years, and Eristaline hoverflies have done comparatively well. There are slight indications that the recent downward trend in abundance of these species is being reversed, but we will really only know if the conditions persist and the fauna responds accordingly.

From a wider perspective it was extremely disappointing to see very few Heleomyzidae and Lauxanidae. Drosophilids were seemingly absent from many sites but we did manage six species of Platypezidae. All-told this was not the most inspiring of Autumn meetings but the company was good and our accommodation was pleasant. On this point I would happily recommend the Northwood Guest House in Rhos on Sea adjacent to Colwyn Bay and Llandudno. It was comfortable, our hosts David and Sandy were excellent, the breakfasts were excellent and we were made very welcome.

I am already planning 2013 meetings. At the moment we think it is time to explore Scotland in September, so a small group is likely to head north in early September. I will arrange a further four-day meeting in the south-east in October; as likely as not this will be based in Reigate, assuming we can make bookings.

My other remaining task is to sort out the venue for the Summer field meeting which I think will be in Lancaster. This is going to be a bit of an adventure because we will use self-catering accommodation at Lancaster University. This choice should bring the cost of the accommodation down to manageable levels for younger members so hopefully we will attract a new cohort of Dipterists from those who have attended recent courses.

Lunch at Newborough Warren - 

Malcolm Smart, Alan Stubbs (standing) Andrew Halstead and John Bratton.

Peter Chandler and Malcolm Smart taking advantage of a sunny spell after torrential rain.

Autumn Field Meeting - update

Today's weather was fantastic. One of those lovely autumn days with warm hazy sunshine. Where were the flies though?

We visited several very nice places but found remarkably few flies. That said, there were a few Platypezidae about and Peter Chandler took three species. Fungus gnats were very scarce, as were Heliomyzidae and Lauxaniidae. There were also very few hovers.

It looks as though the autumn is well and truly established in North Wales and that winter is rapidly setting in. That said, we are still only in early October but the water is jolly cold - I managed a partial dipping today bu losing my footing and falling into a muddy gully. I reckon I am at risk of becoming a liability!

Hoping for good weather tomorrow as we head off towards Colwyn Bay,

Autumn Field Meeting

Two days into the meeing and we are making good progress. It has been hard work though, especially as ever woodland seems to be full of brambles! Last year I described a woodland as a 'bramble patch with a few  trees sticking out of it'. This year the level of bramble infestation is lower but it is still very difficult to avoid shredding one's net!

Impressions so far:

• Fungus gnats numbers are low. Samples are rather homogeneous  and  we have recorded a smaller number of species than at the same time last year.
• Craneflies are in reasonable supply but there are relatively few Tipula species. So far, Limonia nubeculosa has been comparatively scarce.
• There are very few Lauxaniidae - in fact virtually none!
• Drosophilidae are very scarce. 
• Heleomyzidae are in low numbers.
• Hoverflies are scarce but about par for this time of year.

Our group is small but select: Alan Stubbs, Peter Chandler, Andrew Halstead, Malcolm Smart and  John Bratton plus of course yours-truly.

I had a narrow escape today whilst in pursuit of hovers on a patch of rank vegetation, falling  down a manhole whose cover had been removed. I was exceptionally lucky that I escaped with nothing worse than sitting on a few stinging nettles which duly exacted their revenge on me!

We are based in Menai Bridge for this part of the week. It is a place I knew only poorly when based in Bangor  30+ years ago.  Now, it seems positively excellent compared to Bangor; which seems to have few redeeming features. Why on earth did I live there for 3 years?

It is not too late to get out

The weekend approaches and there is still a chance of a hoverfly or two. A few are really dominant, most notably Eristalis tenax. There are plenty of places where this relatively abundant species has yet to be recorded, so a bit of effort may mean a new ten km square record (see map on HRS website for the gaps http://www.hoverfly.org.uk/portal.php?id=10959&scol=HFF0000&bkgrd=1&ecol=H0000FF&page=4). Sericomyia silentis also tends to visit ivy and may be seen occasionally at this time of year. Records are still arriving via ISpot.

October can be an extremely good month of Arctophila superbiens, which is mainly a northern and western species, but it does still occur in North Norfolk and it would be good to see more records from eastern England as well as from more western and northern localities.. This is a species that we think is likely to decline in southern regions as a consequence of climate change, so the more records we get the better its fortunes can be tracked. If it is a nice day, why not go on a quest for this hoverfly in October.

Finally, those in East Anglia should not forget the possibility of Callicera spinolae. It could turn up almost anywhere and has been found in urban parks, formal gardens and in woodlands. A peruse of the ivy patches is a worthy pursuit. But, beware, C. aurata can also fly late and is jolly similar.

As a general point it is worth noting that all records from this time of year are welcome. People tend to hang up the net and the notebook but there are flies to be seen. I noted seven species at a local ivy patch the other day and am hoping for lots of flies when we get to North Wales for Dipterists Forum's Autumn Field Meeting which starts tomorrow.

Ash dieback - a threat to Criorhina and other saproxylic hoverflies

A couple of days ago a friend drew my attention to an article in The Telegraph that highlighted the emerging risk of a new threat to Britain’s trees: Ash dieback caused by the fungus Chalara fraxinea. The story was deeply alarming, suggesting that it had swept across mainland Europe and was killing the majority of Ash trees that it affected.  In Denmark it is reported that 90% of trees are affected! Amazingly, despite the known problems with this pathogen, imports of trees from continental nurseries has yet to be stopped. This is despite known cases of infected trees reaching the UK via the nursery trade. At the moment all known cases involve trees whose health seems to have been monitored, allowing intervention to take place and infected stock to be destroyed. It can surely be just a matter of time before the disease takes a hold unless some urgent action is taken?

Although Ash does not immediately register in the lexicon of important trees for insects, it is actually of considerable interest, especially for the saproxylic diptera that are associated with rot holes and rotting stumps and roots. Woodlands on the borders of Lincolnshire and Northamptonshire are a good example. I never cease to be amazed at the numbers of all four of our Criorhina species in local woods. Two species really stand out: C. asilica and C. ranunculi; neither of which was very abundant in my former stomping ground in Surrey. In northern Northamptonshire they are really quite common and I would expect them to turn up in most long-established Ash woods. I was puzzled by this difference until I discussed it with Alan Stubbs who drew my attention to the key difference in the woodlands.  Those around Stamford support a high density of Ash, whereas in Surrey Oak is much more dominant.

This one small observation makes me very nervous about the future of Britain’s saproxylic hoverfly fauna. Not only would Ash dieback have devastating landscape implications; it would seriously affect one of our most important habitats. The critical issue is that of habitat continuity and in the case of saproxylics that has got to be a key consideration. It is no surprise that ancient woodlands are richer for saproxylics, as they represent the most constant supply of habitat.

What can be done? Probably not a lot, but there is a consultation on the risk assessment by FERA – see http://www.dardni.gov.uk/index/consultations/active-consultations/consultation-by-fera-on-ash-dieback.htm.

This apart, it seems to me that there is an obvious need for urgent measures to survey our Ash woods to determine their real importance for saproxylic invertebrates. This could form a large-scale citizen science project to evaluate Britain's woodlands for the threat Ash dieback poses to one element of our wildlife. 

Episyrphus balteatus in 2012

In my post yesterday I touched on the low numbers of Episyrphus balteaus recorded this year. This is made much clearer by comparing the data for the years 2010, 2011 and 2012 (graph below). The graph was compiled solely from photographs posted on websites and as such it is incomplete. The messages that it conveys are, however, a useful indication of the pwer of ad-hoc recording that is based on what non-specialists actually see.

Figure 1. Relative frequency of Episyrphus balteatus in 2010, 2011 and 2012 against week number (sequential from 1 January).

There is one very clear similarity between the three years: they each show a distinct peak in occurrence towards the end of July, followed by a rapid decline in numbers towards September. The differences are more striking, however:

In 2010 there seemed to be little or no occurrence prior to the spike at the end of July and the period of peak occurrence lasted for no more than five weeks.

In 2011, despite the very cold winter of 2010/2011 there were regular records throughout the winter. Small peaks prior to July suggest that numbers were gradually building prior to the main peak which started in mid-July and ended in early September.

In 2012 the spring was very early and it appears as though one or two small emergences took place prior to the main peak which commenced in mid-July and rapidly fizzled out. The drop in numbers at the end of August remains a constant feature.

What do these data tell us about Episyrphus balteatus populations?

Each graph tells a different story. My initial interpretation of the spike in 2010 is that this largely represents an influx based largely on continental migrants. A similar situation obtains for 2011 although this appears to involve two spikes, possibly reflecting native bred and continental populations? The picture for 2012 suggests that neither the native or the continental spikes really happened.

These data are only a proportion of the data available and a clearer picture should emerge when we analyse the Recording Scheme dataset. That will be some time in the future as there will be several months before the bulk of this year's data arrive and are processed. However, it does seem that the phenology of E. balteatus offers some interesting trends that might be linked to climate variation and which in turn might help to inform predictions about the ways in which critical predaceous species may respond to differing scenarios of climate change.

Hoverfly abundance in 2012 - some early indications

In an earlier post on Volucella zonaria, I highlighted the difference of opinion between my interpretation of Volucella zonaria's  abundance in 2012 and the interpretation in Buglife's press release. I have now done a little bit of analysis which I think sheds light on what has happened this year.

The most compelling evidence for an unusual number of records is that of Helophilus trivittatus which has occurred in exceptionally large numbers. Meanwhile, lots of observers have noted that Episyrphus balteatus has been particularly scarce. Numbers of Volucella zonaria do not appear to me to have been exceptional and a basic analysis of the data from the photographic record seems to confirm this. In order to get a broader picture I also looked at Volucella inanis which has some similar characteristics and is equally noticeable and recordable.

In the past few years I have assembled a dataset of  over 9,800 records from photographs on the web and sent to me as casual inquiries or reports. This dataset is interesting because it largely reflects the species that are seen by the general public and as such is representative of the reports that might have stimulated Buglife's press release.

The data show some interesting trends for 2012.

Aphidophage and aquatics

Figure 1. relative frequencies of Episyrphus balteatus, Eristalis intricarius and Helophilus trivittatus 2004 - 2012

Episyrphus balteatus as a proportion of records has fared very badly with around half the long-term average number of records.

Eristalis intricarius appears to have done relatively well but its numbers do not exceed those of the better previous years

Helophilus trivittatus has had an exceptional year with three times more than the long-term average of records.

Social wasp and bee associates

 Figure 1. Relative frequencies of Volucella species from 2004 to 2012.

Volucella bombylans shows no obvious trend with numbers bouncing around within a consistent level of variation..

Volucella inanis seems not to have changed greatly in its frequency over the past three years and numbers lie below the long-term average which is skewed by data for 2004.

Volucella pellucens appears to have occurred in similar numbers to previous years, but shows a marked drop in frequency in 2011 and a recovery in 2012.

Volucella zonaria numbers are marginally up on the long-term average, but at such a low level that it is difficult to see any reason to assume that anything unusual has happened this year. Part of the reason that numbers are elevated is that additional data arrived via Buglife (about 10% of the sample) and consequently the figures are skewed. Removing these data from the sample would bring the proportion down to 4.89% and this equates to marginally above the long-term average (4.74%) which is not statistically significant.

Analysis

The data presented above are extremely preliminary and will need to be compared against the bigger dataset in the Hoverfly Recording Scheme but they do seem to confirm some of the apparent trends for 2012.

The poor performance of some aphidophagous species is clearly illustrated by Episyrphus balteatus. I will return to this on another occasion as it seems that some greater analysis is needed for this guild.

By comparison, the Eristalines appear to have done exceptionally well.  This must also be a point of further investigation but the data for both Helophilus trivittatus and for Eristalis intricarius, both of which have not been particularly obvious in recent years, suggests a strong gain in numbers.

The data for Volucella zonaria are interesting, however, when you look at the numbers of records in 2011. This shows a quite clear dip in the numbers relative to other species and suggests that V. zonaria was not as frequent in 2011. The reason for this is most likely to be a response to the exceptionally cold winter of 2010/11. There are precedents as Stuart and I showed in our papers exploring the responses of Volucella zonaria and V. inanis over the past 60 years (see http://www.bacoastal.co.uk/Entomology/2004-Volucella-zonaria.pdf and http://www.bacoastal.co.uk/Entomology/2003-Volucella-inanis.pdf). Both species underwent substantial range contraction in response to the cold winter of 1963, but clearly that was considerably more dramatic than that of 2010/11. It is also very noteworthy that a similar dip can be detected in Volucella pellucens which I did not expect. Further analysis is needed for this species too.

Looking at the data, I suspect that any detailed analysis should omit the data for 2004 and 2005 because there were few photographic records exist for those years - see below. However, what is also becoming clear is that web-based data may prove to be a useful means of monitoring certain aspects of the country's biodiversity, even though it has significant limitations because only a proportion of the fauna can be identified from photographs.

Figure 2. Numbers of photographic records from internet sites from 22004 to 2012.