Photographic records of Hoverflies collated in 2015: a preliminary

analysis

Roger K.A. Morris, Stuart G. Ball, Ian Andrews,

Joan Childs & Ellen Rotheray

February 2016

Eristalis pertinax (Linnaeus, 1758) in flight. Photography by Tony Mathews

Recommended citation: Morris, R.K.A., Ball, S.G., Andrews, I., Childs, J. & Rotheray, E., 2016. Photographic records of Hoverfly collated in 2015: a preliminary analysis. Unpublished report by the Hoverfly Recording Scheme.

Copyright UK Hoverfly Recording Scheme. Please note that the data presented in this report should not be used directly in papers submitted for publication without the express permission of the authors, although the findings quoted herein may be referred to. Contact address: Roger K.A. Morris, 7 Vine Street, Stamford, United Kingdom PE9 1QE. roger.morris@dsl.pipex.com

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Executive Summary

1. Interest in photographic recording of hoverflies continued to grow in 2015, with overall volumes of data from such sources more than doubling compared with the data for 2014.

2. The numbers of contributors in 2015 is slightly lower than for 2014. There were 1,007 recorders, of which 528 are not previously represented in the dataset

3. The numbers of people contributing more than 20 records has risen steeply and the numbers contributing more than 100 records are also considerably higher. This rise in recorder activity is directly attributable to the establishment of the UK Hoverflies Facebook page.

4. Most recorders and records still come from the south and the Midlands, but there are

signs of improvement in recorder activity in more northerly regions. This improvement includes the work of several very active recorders whose datasets are making an important difference to our ability to monitor hoverflies north of a line between the Humber and the Mersey.

5. A total of 150 species were recorded from photographs in 2015. This list includes several red-listed species.

6. The composition of the 50 most frequently recorded species remains broadly similar to 2014, with just three new species entering the list and 3 being displaced.

7. The four most frequently recorded species remain in the same rank order of abundance. The main movement in 2015 suggests that aphidophagous species were slightly more abundant and associates of wasp nests rather less frequently recorded.

8. The analyses show how data from ad-hoc sources can be used in a variety of ways to investigate hoverfly ecology. Some of these analyses will benefit from an increased recorder base and from the very diligent recording now practiced by several Facebook members.

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iii

Contents

Executive Summary .............................................................................. i Contents ................................................................................................. iii-iv 1. Introduction ................................................................................................. 1 2. Basic statistics ................................................................................................. 2

2.1. Proportion of photographs identified .................................................... 3 2.2. Numbers of recorders ......................................................................... 5 2.3. Spread of records over the year ........................................................... 5 2.4. Geographic coverage ............................................................................ 8 2.5. Most frequently represented species in the general photographic

database ..... 8

3. Some critical misconceptions and questions .................................................. 12 3.1. ‘Photographers only see common species?’ .......................................... 12 3.2. ‘Only a small proportion of the fauna can be identified from

photographs?’ ............... 14

3.3. ‘Data from photographers will skew the dataset’ ................................. 14 3.4. ‘How can photographic recording improve our knowledge of

hoverfly biology’?’ .............. 15

3.5. ‘What use is data that is not collected according to defined protocols?’

................ 22

3.6. ‘How can photography advance our knowledge of hoverfly taxonomy?’

................ 23

4. References ..................................................................................................... 24 Appendices .....................................................................................................

1. Species list of hoverflies recorded from photographs accessed in 2015

...... 25

2. Detailed breakdown of the representation of British hoverfly genera within the 2014 photographic database

...... 27

Tables 1. Photographic records not supported by specimens extracted

from electronic media in 2015. ...................... 4

2. Photographic records by John Bridges in which a proportion of the subject matter (around 300 specimens) was retained and forwarded for critical identification.

............. 4

3. Rank order of the most frequently recorded hoverflies in the photographic database in 2015.

...................... 11

Figures 1. Yearly growth in the photographic dataset between 2004 and 2015. .......... 2 2. Numbers of identified photographic records extracted in each of the

years 2013 to 2015 represented at Log2 scale. .......... 3

3. Numbers of records contributed by individual recorders for the years 2013 to 2015 represented at Log2 scale.

.......... 5

4. Three week centred running mean of the weekly proportions of records for 2014 and 2015.

.......... 6

5. Monthly charts for the four most likely weather parameters that

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might be expected to influence the numbers of hoverflies recorded by photographers. 5a. Monthly average temperature across the UK in 2014 and

2015. .......... 6

5b. Average sunshine hours across the UK in 2014 and 2015. ................. 7 5.c. Average days of air frost across the UK in 2014 and 2015. ................. 7 5.d. Average days ran across the UK in 2014 and 2015. ............................. 8

6. 6a. Distribution of all fully identified photographic hoverfly records in 2015.

................... 9

6b. Distribution of all fully identified photographic hoverfly records in 2014.

................... 9

6c. Numbers of fully identified photographic records for individual

10 km squares in 2015. .............. 10

7. A selection of the rarer hoverflies recorded by photography in 2016.

7a. Callicera aurata (Rossi, 1790) ............................................................. 13 7b. Doros profuges (Harris, 1780) .............................................................. 13 7c. Mallota cimbiciformis (Fallén, 1817) .................................................. 13 7d. Meligramma euchromum (Kowarz, 1885) ........................................... 13 7e. Meligramma guttatum (Fallén, 1817) .................................................. 13 7f. Pelecocera tricincta Meigen, 1822 ...................................................... 13

8. Phenology of the four hoverfly species most frequently recorded in winter months (data covering November 2014 to 15 January 2016).

............ 17

9. Numbers of contributors to the photographic dataset with records between 01 November and 31 December represented at log2 scale.

............ 17

10. Phenology of males and females of the four hoverfly species most frequently recorded in the months from November to March.

10a. Episyrphus balteatus .......................................................................... 18 10b. Eristalis tenax ..................................................................................... 18 10c. Eristalis pertinax ................................................................................. 19 10d. Meliscaeva auricollis .......................................................................... 19

11. Phenology of Epistrophe eligans in 2015 using a centred 3-week running mean.

..... 20

12. Phenology of Eristalis tenax within 4 UK zones. .............................................. 20 13. The phenology of Cheilosia illustrata in 2014 and 2015.

13a. Phenology of Cheilosia illustrata in 2014. ................................................ 21 13b. Phenology of Cheilosia illustrata in 2015. ................................................ 21

14. Distribution maps of two common hoverflies in Europe. 14a. Episyrphus balteatus .......................................................................... 23 14b. Eristalis tenax ..................................................................................... 23

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Eristalis rupium Fabricius,

1805

In this photo the pale hind

tarsi and the strong wing

shade are well caught.

Photo: Gavin Chambers

Sphegina sibirica

Stackelberg, 1953

A piebald variant that is

difficult to confuse with other

British Sphegina.

Photo: Paul Johnston

Xanthogramma stackelbergi

Violovitsch, 1975

Three angles showing the

tight wing cloud, extensive

yellow on the thoracic

pleurae and very narrow

black band on the frons.

Photos: Graham Watkeys

Three of the more unusual finds of 2015. In each case the photographs are examples of several

records submitted in 2015.

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1. Introduction

A first report on data secured from photographic sources for all families of Diptera extracted in the years up to 2014 was produced by the Hoverfly Recording Scheme (HRS) (Morris & Ball, 2015). The report highlighted a remarkable increase in interest in hoverflies and in photographic recording. Further increases in interest and activity mean that it has not been possible to maintain an overview of all Diptera recording from these sources. As a result, this report solely focuses on data relating to hoverflies.

In 2015 HRS expanded its capacity to meet growing demand for assistance with identification of photographs. Ian Andrews, Joan Childs have joined the team providing identifications to the UK Hoverflies Facebook (FB) page. In addition, Ellie Rotheray has joined us and is starting to build a broader constituency of interest in larvae and has established a separate FB page dedicated to hoverfly larvae. This expanded team will hopefully be able to cope with demand but there remains the possibility that further recruitment will be needed to make sure that the scheme has the depth and breadth of skills and capacity to engage pro-actively with interested natural historians and photographers.

Details of the methods used in extracting data are provided in our report for 2014. Similar techniques were used this year and readers are therefore referred back to the first report as a baseline document. This new report concentrates on giving feedback on the on the data assembled in 2015.

Photographic recording is rapidly becoming a major component of all biological records submissions. In the case of the HRS the growth has been extremely fast. This report has been constructed to provide feedback to the UK Hoverflies Facebook group. It presents data in a series of ways, which it is hoped will explain why we seek the level of detail asked for.

Although the data are robust, it is likely that there will always be sceptics who doubt its value. A series of rhetorical questions are therefore posed, together with an analysis of the data, to establish the veracity of possible challenges.

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2. Basic statistics

In common with previous years, there has been continuing growth in the numbers of records posted as photographs on the internet (Figure 1). Much of this can be attributed to a substantial increase in the activity of the UK Hoverflies FB page. Membership of the FB group climbed from around 1,300 members in January 2015 to around 2,050 by the end of December 2015. Had it not been necessary to suspend recruitment for two months during August and September this number might have been a great deal higher.

At the moment there is no sign that the level of activity and record submission is approaching an asymptote and it is likely that we will see further growth for at least one or two seasons providing there is not a decline in activity by existing site members.

Figure 1. Yearly growth in the photographic dataset between 2004 and 2015.

The influence of the UK Hoverflies FB page is very clear; building on the impact it had in 2014 and setting a new peak that now represents a significant part of the data reaching the HRS. Its influence is much wider than simply influencing the numbers of records: there has been a detectable change in the numbers of records from the various internet sources. Firstly, some former members of the now defunct forum 'Wild About Britain' have joined the FB group and make a significant contribution to the data. In addition, the numbers of hoverflies posted on iSpot seem to have declined. Whether this can be attributed to the FB group is unclear, but the drop in numbers is substantial (Figure 2). A further change has been the separate contribution of John Bridges whose data are submitted by spreadsheet and supported by photographs on his personal website (North East Wildlife); hence the decline in use of the HRS website and the arrival of a new data source.

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Figure 2. Numbers of identified photographic records extracted in each of the years 2013 to 2015

represented at Log2 scale.

2.1. Proportion of photographs identified In 2015 there has been substantial diversification of recording linked to photography. Some Flickr users now submit their data via iRecord - removing the need for RKAM to extract data from their posts. Similarly, a number of FB members maintain their records without submitting every photograph for identification by the resident team. Consequently, the database of photographic records discussed here represents only a part of the data that ultimately reach the HRS database. Several of these recorders are contributing garden monitoring data that is growing and will hopefully reach a point where it is possible to undertake separate analysis.

This central core of photographic data provides the basis for understanding what recorders normally see and the sorts of problems they encounter when trying to put names to individual animals. In addition, one FB member (John Bridges) now retains specimens (if possible) after they have been photographed, freezes them and passes them on to RKAM for checking. As a result, those records that are not supported by specimens and those that are can be analysed separately.

Comparison between the two data sets shows clearly how the reliability of data can be reinforced by retaining specimens. Overall numbers of photographs where a firm identification was possible is substantially greater, but inevitably there were specimens that eluded capture (e.g. all Eumerus and Paragus) or where it was not realised that there might be a need for a corroborating specimen. The angles of individual photographs can be very important and it is not always possible to get the precise angle required to show the critical features (e.g. a few Eristalis). Achievement of a 100% success rate is therefore highly unlikely and anything above 90% is probably as good as one might hope for. 2015 was an experimental year for retaining specimens and there have been important lessons learned. It will therefore be very interesting to see what is achieved in 2016.

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Table 1. Photographic records not supported by specimens extracted from electronic media in 2015.

Tribe GB & Ireland Fauna

Species positively identified

% GB fauna in sample

recorded

Total records

Records identified

%records identified

Bacchini 30 16 53.33 3,158 2218 70.23

Callicerini 3 3 100 9 9 100

Cheilosini 43 19 44.19 1679 1344 80.07

Chrysogastrini 29 12 44.83 492 211 43.00

Eristalini 28 19 67.86 7,198 6540 90.86

Merodontini 7 2 28.57 563 480 85.26

Microdontini 4 2 50 8 6 75

Paragini 4 0 0 12 0 0

Pelecocerini 3 1 33.33 1 1 100

Pipizini 20 3 15 133 19 14.29

Sericomyiini 3 3 100 429 429 100

Syrphini 84 50 59.52 9,808 6924 70.60

Volucellini 5 5 100 1219 1211 99.34

Xylotini 20 15 75 1249 1224 98.00

Uncertain 0 0 10 0 0

Totals 283 150 53.00 25968 20616 79.3900

Table 2. Photographic records by John Bridges in which a proportion of the subject matter (around

300 specimens) was retained and forwarded for critical identification.

Tribe GB & Ireland Fauna

Species positively identified

% GB fauna in sample

recorded

Total records

Records identified

% records identified

Bacchini 30 14 46.67 511 495 96.87

Callicerini 3 0 0 0 0 0

Cheilosini 43 16 37.21 361 310 85.87

Chrysogastrini 29 10 34.48 122 116 95.08

Eristalini 28 13 46.43 632 606 95.89

Merodontini 7 1 14.29 12 8 66.67

Microdontini 4 0 0 0 0 0

Paragini 4 0 0 1 0 0

Pelecocerini 3 0 0 0 0 0

Pipizini 20 3 15 25 14 56

Sericomyiini 3 1 33.33 2 2 100

Syrphini 84 30 35.71 977 832 85.16

Volucellini 5 2 40 102 102 100

Xylotini 20 8 40 208 208 100

Uncertain 1 0 0

Totals 283 98 34.63 2954 2693 91.16

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2.2. Numbers of recorders In each of the past three years, the number of photographic recorders has exceeded 1,000 but there was a downward drift in numbers in 2015, possibly because less attention has been paid to Flickr sources. In 2015, there was a total of 1,007 recorders, of which 528 are not previously represented in the dataset. The data seem to indicate that there is a substantial amount of turnover amongst the recorder community, which is inevitable because many people who post on iSpot and Flickr have wide-ranging interests and may not have any firm preference for hoverflies.

Data for the past three years (Figure 3) suggests, however, that there has been a fundamental change in recorder activity, with considerably more people posting multiple records and a remarkable number (46) who submitted 100 or more records. These totals are augmented by other FB members who now submit records by spreadsheet, often contributing many hundreds or thousands of records for the year. This is a tremendous addition to the recorder community and will make detailed analysis of the full database much more instructive.

Figure 3. Numbers of records contributed by individual recorders for the years 2013 to 2015

represented at Log2 scale.

These results convey several important messages in the context of the wider biological recording community. Most importantly, there is a tremendous appetite amongst photographers and natural historians to get involved with interactive media in which there is rapid feedback and the development of a 'community' spirit.

2.3. Spread of records over the year During the course of the year, the data started to suggest that there were differences in the abundance of hoverflies when compared to 2014. This was most pronounced in the autumn, which was markedly warmer in November and December, during which several recorders reported large numbers of hoverflies on a regular basis. Individual weekly totals are markedly variable, and therefore it is very difficult to make direct comparisons between 2014 and 2015. The data were therefore turned into weekly proportions of the year’s total

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before a 3-week centred running mean was applied. This process results in more readily interpreted charts.

The numbers of records in the early part of 2014 and 2015 were broadly similar (although 2014 may have been fractionally more active in March and April) (Figure 4). In both years the peak of hoverfly abundance appears to have been late July and early August, but striking differences emerge in late summer and autumn, when the effects of late warm weather are clear. Comparison with average temperatures, sunshine hours and air frosts (figures 5a to 5c) (Met Office Data) indicates that all three factors combine to influence the data. The numbers of days with rain appear to have little correlation, possibly because hoverflies will often emerge in large numbers after rain, providing temperatures rise and there is sunshine.

Figure 4. Three week centred running mean of the weekly proportions of records for 2014 and 2015.

Figure 5a. Monthly average temperature across the UK in 2014 and 2015.

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Figure 5b. Average sunshine hours across the UK in 2014 and 2015.

Figure 5c. Average days of air frost across the UK in 2014 and 2015.

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Figure 5d. Average days ran across the UK in 2014 and 2015.

Figure 5. Monthly charts for the four most likely weather parameters that might be expected to

influence the numbers of hoverflies recorded by photographers. The numbers of days of rain and its

duration seem likely to be responsible for the dip in records in May 2014 (Figure 4).

2.4. Geographic coverage Although overall coverage (Figure 6a) looks broadly similar to 2014 (Figure 6b) there are a number of important differences. Most significantly, there is markedly better coverage for north and south Wales, Lincolnshire, Cumbria and other locations in northern England, and for several parts of Scotland. Overall there was more recording in southern England, whilst there remains a noteworthy absence of recording from many parts of central Wales and from western Scotland. All of these features are consistent with wider experience of data entering the HRS, with the most of records close to major centres of population.

The picture emerging from the numbers of records from individual 10km squares (Figure 6c) also shows important progress with a growing number of relatively well-recorded squares. The spread of well-recorded locations is greatly encouraging because in recent years the HRS dataset has largely been dominated by southern recorders. A more balanced coverage will help to improve data suitable for detailed analysis of the influences of climate on hoverfly distribution.

2.5. Most frequently represented species in the general photographic database Table 3 presents the data for the 50 commonest species in 2015 and 2014. As might be expected there are close similarities between the two years, but also some substantial differences. For example, aphid-predators seem to have fared better in 2015. Conversely, it is noticeable that records of the wasp-nest dwelling Volucella appear to have fared far less well than in 2014. Differences of this nature are inevitable as two consecutive years will vary in many ways and it is to be expected that some species will be more abundant in one year than another.

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The differences are potentially important because they indicate that data from this source will be sufficiently sensitive to annual fluctuations that they can be used to investigate wider aspects of environmental change. At this stage, however, the differences may also be attributed to changing recorder behaviours. As Figure 3 shows, there has been a significant change in the behaviours of recording; with fewer contributors of single records and substantial growth in the numbers of recorders making more comprehensive records of a wider spectrum of taxa.

Several of the FB group members have become regular observers, recording everything that they see on a given visit. This approach to recording is especially welcome as it in many ways parallels the site species list concept used in Birdtrack. Birdtrack uses the proportion of the complete lists for a visit in which a given species was recorded to present year-on-year differences in bird occurrence. Perhaps a similar approach would be possible for hoverflies? This is part of the conceptual approach that we hope to develop for the garden hoverfly monitoring scheme. A network of people who make regular, complete lists is an essential stage in establishing a long-term monitoring scheme that is capable of identifying changes in hoverfly abundance.

Figure 6a. Distribution of all fully identified photographic hoverfly records in 2015.

Figure 6b. Distribution of all fully identified photographic hoverfly records in 2014.

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Figure 6c. Numbers of fully identified photographic records for individual 10 km squares in 2015.

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Table 3. Rank order of the most frequently recorded hoverflies in the photographic database in 2015

Species Rank 2015

Rank 2014

Change Habitat Species Rank 2015

Rank 2014

Change Habitat

Episyrphus balteatus 1 1 Even Aphids Eristalis intricarius 26 21 Down Wetland

Eristalis pertinax 2 2 Even Wetland Volucella inanis 27 18 Down Social Hym.

Eristalis tenax 3 3 Even Wetland Syrphus torvus 28 31 Up Aphids

Helophilus pendulus 4 4 Even Wetland Leucozona lucorum 29 28 ~ even Aphids

Platycheirus albimanus 5 11 Up Aphids Epistrophe grossulariae 30 30 Even Aphids

Syrphus ribesii 6 12 Up Aphids Chrysotoxum bicinctum 31 29 Down Ant tended aphids

Melanostoma scalare 7 6 ~ even Aphids Baccha elongata 32 32 Even Aphids

Myathropa florea 8 5 Down Wetland Meliscaeva cinctella 33 38 Up Aphids

Eupeodes luniger 9 14 Up Aphids Dasysyrphus albostriatus 34 35 ~ even Aphids

Syritta pipiens 10 7 Down Saproxylic Cheilosia albitarsis sl. 35 - Up Plants

Rhingia campestris 11 9 Down Dung Eristalis horticola 36 42 Up Wetland

Merodon equestris 12 13 ~ even Plants Eristalis interruptus 37 33 Down Wetland

Volucella pellucens 13 8 Down Social Hym. Chrysotoxum festivum 38 37 ~ even Ant tended

Sericomyia silentis 14 17 Up Wetland Platycheirus scutatus sl. 39 49 Up Aphids

Sphaerophoria scripta 15 15 Even Aphids Chrysogaster solstitialis 40 40 Even Wetland

Xylota segnis 16 16 Even Saproxylic Xanthogramma pedissequum sl. 41 27 Down Ant tended aphids

Scaeva pyrastri 17 23 Up Aphids Xanthogramma pedissequum ss. 42 - Up Ant tended aphids

Volucella zonaria 18 10 Down Social Hym. Cheilosia pagana 43 50 Up Plants

Meliscaeva auricollis 19 22 Up Aphids Ferdinandea cuprea 44 41 Down Sap runs

Cheilosia illustrata 20 25 Up Plants Platycheirus manicatus 45 46 ~ even Aphids

Eupeodes corollae 21 20 ~ even Aphids Xylota sylvarum 46 43 Down Saproxylic

Eristalis arbustorum 22 19 Down Wetland Eristalinus sepulchralis 47 44 Down Wetland

Epistrophe eligans 23 24 ~ even Aphids Rhingia rostrata 48 45 Down Dung

Volucella bombylans 24 26 Up Social Hym. Helophilus hybridus 49 48 ~ even Wetland

Leucozona glaucia 25 36 Up Aphids Tropidia scita 50 - Up Wetland

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3. Some critical misconceptions and questions

Although photography is an increasingly popular way of making biological records, it is not universally accepted as a valid approach. Many traditional taxonomists question its potential and the value of encouraging such an approach. A relatively small proportion currently engage positively. A wide range of less constructive views are often expressed.

The traditional preserved specimen, microscope and keys will continue to be an essential part of taxonomy, but we must accept that new technology will have a significant impact in the next century. Advances in DNA analysis are an obvious way in which taxonomic ideas may be revised. Photography also has an important role to play, especially when one thinks about the differences between living and preserved specimens.

Photography is potentially as important as DNA analysis when translating revised taxonomic thinking into a format that can be used by the modern field biologist. The big issue is to start to understand both its potential and its limitations. The following rhetorical questions are therefore posed as a way of teasing out some of the issues in relation to hoverfly recording. The answers relate strictly to hoverflies and may not be applicable to other families of flies; many of which will continue to require microscopic examination.

3.1. ‘Photographers only see common species’ It is true that the majority of records from photographs involve the commoner species, but the same situation obtains for most records submitted to the HRS from other sources. Rare species will always form a relatively small part of the dataset so there is no reason to discount photography as a way of generating records just because the bulk of records are of commoner species. The issue of representation of rare species in the dataset is complicated because there are several types of contributors:

i. Casual recorders who submit less than ten records yearly and often provide just one or two records.

ii. Intermittent recorders who take a passing interest on one or a series of days and generate between 10 and 30 records per year.

iii. Recorders whose interest is sufficient to make observations on a comparatively regular basis but who generally do not attempt to produce comprehensive lists. Such recorders can produce substantial datasets but they may not attain the depth of coverage that specialists achieve.

iv. Developing specialists whose data often represent the full spectrum of species seen, but possibly lack species that require special search techniques.

v. Specialists who attempt to record everything that they see on a particular visit.

Although there is the temptation to assume that only the more specialised recorder will find the rare or unusual species, this is a long way from reality. In 2015, 20 scarce and threatened species listed in Ball and Morris (2014) were recorded by photographers; comprising one Vulnerable, two Near Threatened and seventeen Nationally Scarce. Examples are included in Figures 7a to 7h:

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Figure 7a. Callicera aurata (Rossi, 1790)

(Nationally Scarce) (Photo Simon Knott) Figure 7b. Doros profuges (Harris, 1780) (Near

Threatened) (Photo: Graeme Lyons)

Figure 7c. Mallota cimbiciformis (Fallén, 1817)

(Nationally Scarce) (Photo: Sophie Barnes) Figure 7d. Meligramma euchromum (Kowarz,

1885) (Nationally Scarce) (Photo: Alan Prowse)

Figure 7e. Meligramma guttatum (Fallén, 1817)

(Nationally Scarce) (Photo: John Bridges)

Figure 7f. Pelecocera tricincta Meigen, 1822

(Nationally Scarce) (Photo: Nick Baldwin)

Figure 7. A selection of the rarer hoverflies recorded by photography in 2016.

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3.2. ‘Only a small proportion of the fauna can be identified from photographs’ In 2015, a total of 150 species were recorded by photography. The majority of the records relate to 2015 but they extend back to 1999. Tables 1 (above) clearly shows that there are limits to what can be identified. It is difficult to be sure how many species can realistically be recorded by photography alone (some include close-ups taken in the studio), but somewhere in the order of 60% of the UK fauna as it is currently understood seems reasonable. This success rate of identification cannot be translated into other Diptera families or elsewhere into the Class Insecta where there may be many more very similar species.

There is a perception amongst some taxonomists that photographs comprise poorly focused and composed snaps. This is far from the case, although the quality does vary. It is true that there is less chance that a firm identification will be possible if the shot is poorly focussed and/or if the animal occupies a small part of the frame but such photographs represent a comparatively small part of the sample. Many of the contributors to the UK Hoverflies FB page are accomplished photographers as illustrated by Tony Matthews' amazing shot of Eristalis pertinax in flight on the citation page at the front of this report. Photographers who post on Flickr include some of the country's leaders in stacking technology - a long way from the fuzzy snaps envisaged by some sceptics. In addition, many of the FB group have developed sufficient knowledge of the subject matter to know that it is helpful to take photographs from several angles. Consequently, it is not unusual to see multiple photographs of each individual.

It should also be noted that species that can be identified from photographs are not necessarily 'common'. Some of the rarest species are in fact very easy to identify from photographs (e.g. Blera fallax - as yet not photographed by a UK recorder). Major difficulties emerge in genera such as Cheilosia, Sphaerophoria, Platycheirus and Pipiza but in general these genera are poorly represented in the dataset because they are not immediately recognised as hoverflies, or because they occur in situations that are not regularly visited by photographers.

The data produced by John Bridges (Table 2) help to show what can be achieved by a photographer who takes a detailed interest in the family and starts to record everything encountered. This dataset is unusual because in about 10% of cases, the specimens were retained and subsequently identified by RKAM. This approach means that there is a developing database of photographs of 'difficult' species.

It should be noted that the conventions used on the UK Hoverflies Facebook page focus on what can and cannot be firmly identified - all three of the resident team (IA, JC and RM) will not identify shots to species without being confident that the critical features are adequately depicted. This rigour is essential if the dataset is to be reliable, and its constant reinforcement helps to make sure that the recording community follows similar protocols.

3.3. ‘Data from photographers will skew the dataset’ It should be borne in mind that there has always been a tendency for traditional recorders to limit record submissions to species that they consider to be “of interest”. The value of full species lists is often overlooked or is not fulfilled because the effort involved is more than recorders are willing to commit to. Consequently, the historic dataset is skewed towards rarer species. This is especially true for museum specimens, where there is a comparative

15

over-representation of showy or rare species. In addition, it is also common for recorders to limit their yearly submissions to their first records only. One often gets the comment ‘I will send first and last records but I have not got the time to bother with all records’.

Both traits are frustrating if one wants to develop a dataset that is representative of the occurrence of hoverflies over the whole year. The development of a community of recorders that does not discriminate between rare and common species, or between those previously seen and those that are new, is therefore an important improvement in the reliability of the data.

Relatively few contributors to the HRS record across all taxa, especially the more difficult to identify (Cheilosia, Pipiza and Sphaerophoria). Past comparisons (unpublished) by RKAM have shown that species lists prepared by full taxonomic survey are composed of a substantially different fauna, with more Cheilosia, Chrysogastrines, Pipizines and some Platycheirus and Sphaerophoria. More work is required to make detailed comparisons and may be attempted in due course. Comparison with HRS data (unpublished) also shows that the composition of the HRS data lies part way between those of the photographic recorders and those of full taxonomic lists. Data assembled by John Bridges more closely approximates to the full taxonomic survey and may be closer still in 2016 as this is only his second year of detailed recording.

3.4. ‘How can photographic recording improve our knowledge of hoverfly biology?’ We still do not fully understand many aspects of hoverfly biology, despite several decades of recording and autecological investigations. One obvious benefit of photographic records is that it should be possible to build a more complete picture of flower visits by hoverflies. Such information may be of great interest to academic pollinator studies and is often lacking from data supplied to the recording scheme by traditional recorders.

Data from traditional sources are very useful in defining hoverfly phenology, but analysis has always lacked precision because too few records are received each year to allow detailed between year comparisons. The more data that are available on each yearl, the better we are able to explore ways in which hoverflies are responding to environmental change. Photographic recording offers a really good chance of building a dataset that will help to define the ways in which hoverfly flight times change on a yearly basis and according to different latitudes.

In 2015 one of the most remarkable results from the FB group was the level of information that has been generated on hoverfly activity in the autumn and early winter. This data would not have been possible if sought from traditional Dipterists because most cease recording after the middle of September. FB group members, in contrast, have kept going throughout the winter, providing possibly the first ever full dataset on the species that occur in mid-winter and an indication of the numbers involved. Several recorders managed to keep going throughout this period and together they showed that there are actually many more hoverflies active in November and December than had hitherto been thought likely (Figure 8). Several remarkable late records were reported. A December record for Sericomyia silentis in the final week of the year was exceptional. Reports of high numbers of hoverflies at dandelion flowers in Co. Durham are also noteworthy as these sometimes amounted to several hundreds of individuals. Similar experience (in lower numbers) at sites in Lancashire and Devon provide further evidence that under certain conditions hoverflies can be very

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active in winter months. The use of sugar sprays at some sites also proved to be very effective in attracting low numbers of hoverflies, suggesting that this technique might be useful in other contexts.

The autumn and early winter of 2015-16 was exceptionally mild and the numbers of hoverflies seen was possibly higher than usual. We cannot be sure that this is the case because there are no comparative data: in 2013 and 2014 the numbers of recorders within the FB group were much lower and levels of activity by individual members were lower. Data from the most prolific winter recorders suggests that there are actually quite high levels of hoverfly activity on mild days, and that plants such as Vibernum tinus are potentially important nectar sources. Further recording in the future should help to establish year-on-year fluctuations in winter hoverfly abundance.

One of the big advantages of extracting records from photographs has been our ability to develop large datasets in which the accuracy of identification has been standardised. In addition, the datasets include all information on flower visits and on the gender of the individuals recorded. This is exceptionally valuable because there is always an element of doubt where data sets are not supported by voucher specimens. In the case of web-based photographic recording, the URL for the photographs is effectively a voucher specimen that allows some element of re-scrutiny should this be necessary. The permanency of URLs may is not guaranteed, but in many cases they can be expected to last for several years. Those that are lost are effectively analogous to specimens discarded by the recorder or to the impact of pests in collections!

Development of a large dataset for relatively common species, in which the gender is recorded means that it is possible to investigate some aspects of the phenology of males and females and therefore to tease out some of the differences between individual species.

Data assembled from a web-based community of active recorders differs from that of traditional recorders because ongoing reports of hoverfly activity help to encourage more diligent recording at relatively un-productive times of year. Most traditional Dipterists would cease recording by the end of September or possibly October, whereas in 2015 it has been possible to harness the enthusiasm of a substantial group of recorders, 88 of whom contributed at least one record between 01 November and 31 December 2015 (Figure 9).

The work of a large group of recorders in autumn 2015 has helped show subtle differences in the population biology of individual species that would not have been possible in previous years. It has long been suspected that some hoverflies other than Eristalis tenax actually overwinter; but which ones? The developing data help to identify the differences: those that are continually brooded (e.g. Meliscaeva auricollis) (figure 10d) from those in which the females over-winter (Eristalis tenax and Episyrphus balteatus) (Figures 10a and 10c), and those in which the flight time is extended by autumn temperatures (e.g. Eristalis pertinax) (Figure 10b).

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Figure 8. Phenology of the four hoverfly species most frequently recorded in winter months (data covering November 2014 to 15 January 2016).

Figure 9. Numbers of contributors to the photographic dataset with records between 01 November

and 31 December represented at log2 scale.

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10a. Episyrphus balteatus: This chart shows how the population is dominated by females between

January and March, which strongly suggests that only females overwinter.

10b. Eristalis pertinax: The phenology of males and females in the winter of 2014-15 seems to differ

from that of 2015-2016, but further recording may eventually reveal broadly similar phenology with

the differences from 2014-15 explained by the longer flight season of 2015.

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10c. Eristalis tenax: There appear to be substantial differences in winter occurrence patterns for males

and females between 2014-15 and 2015-16. It is particularly noteworthy that females appear to have

disappeared in December 2014 but were still partially active in December 2015.

10d. Meliscaeva auricollis: It would appear that this species is continuously brooded.

Figure 10. Phenology of males and females of the four hoverfly species most frequently recorded in

the months from November to March. Wide separation in the proportions of males and females

suggests points at which there is a new population, with males emerging before females and declining

in abundance as females live on after the flush of male abundance.

The HRS dataset, in common with many other recording schemes, has a strong southerly bias in recorder effort, with much lower numbers of recorders in northern England and

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Scotland. Consequently, has been extremely difficult to explore within year regional differences in phenology using the original pool of contributors. Such analyses have had to be undertaken by aggregating the data over several years to get any meaningful output. This weakness has been substantially addressed by the FB group, whose most active recorders are broadly spread across mainland Britain and including both Orkney and Shetland. This expansion of recorder activity is a very significant improvement; making is possible to investigate yearly phenology at different latitudes (Figures 11 & 12). Given the substantial growth in recorder effort at the latter end of 2015 this aspect of improved analysis should be more obvious in 2016.

Figure 11. Phenology of Epistrophe eligans in 2015 using a centred 3-week running mean. Data

remain extremely sparse above the Scottish borders and consequently northern English and Scottish

data are lumped together. This example clearly shows how flight times are delayed with more

northerly latitudes.

Figure 12. Phenology of Eristalis tenax within 4 UK zones. The data are presented as a centred 3-

week running mean of the proportion of total records from that zone. Although Eristalis tenax would

appear to overwinter in all zones, the data point to very limited overwintering in more northerly zones.

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The impact of a growing body of more northerly recorders is illustrated in the case of Cheilosia illustrata (Figure 13). C. Illustrata is a widespread species that is often abundant at umbellifer flowers. It is regularly photographed and is relatively easy to identify from photographs. Moreover, its flight times are strongly influenced by latitude. In 2014, there were considerably fewer recorders, especially in northern England and Scotland. The resulting plots for four zones are confused because the there were big gaps between records in the two northern zones. Thus the plots for the two northerly zones might be misinterpreted or regarded as unrepresentative of the real situation. More records were received in 2015 with several new recorders making regular efforts to record their local ‘patch’. The result is a better plot which is more likely to be representative of the actual situation (Figure 13b). Data for 2015 suggest that more southerly populations may be partially double-brooded.

Figure 13 a. Phenology of Cheilosia illustrata in 2014.

Figure 13b. Phenology of Cheilosia illustrata in 2015.

Figure 13. The phenology of Cheilosia illustrata in 2014 and 2015. The plots derive from a three-

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week centred running mean of the weekly proportion of records for the zone concerned.

3.5. ‘What use is data that is not collected according to defined protocols?’ In an ideal World, there would be monitoring programmes for a wide variety of plants and animals using standardised techniques such as Rothamsted moth survey, and Wetland Bird Survey (WeBS). In both of these examples, the majority of the data are assembled by volunteers, with a small professional team co-ordinating the work and providing data analysis and feedback. Despite extensive use of volunteers, such schemes are extremely expensive and are always vulnerable to cost-saving programmes. Indeed, the Rothamsted survey has been substantially reduced in scale as a result of recent austerity programmes.

It is therefore almost inconceivable that there will ever be sufficient funds to support monitoring of all Britain's wildlife using standardised techniques. We must therefore assume that a comprehensive national monitoring scheme for hoverflies or other Diptera using rigorous recording protocols is unlikely to emerge in the foreseeable future. This situation means that we must rely on alternative data sources and accept their limitations if we are to have any understanding of the status of much of Britain's wildlife. These limitations can be taken into account using a variety of statistical protocols, some of which have been developed using the data assembled by the Hoverfly Recording Scheme.

Almost all of the science that underpinned designation of Sites of Scientific Interest originates from ad-hoc sources; rather than as a result of a comprehensive survey of Britain's landscape to identify the best and most representative sites. Until recently, invertebrate data was much sparser than data for plants and birds. Consequently, invertebrates are generally poorly represented on the original citations for SSSI. Today, the situation is greatly improved, with a far more comprehensive network of recorders and with the necessary data storage capacity. Nevertheless, we still know far less about the distribution of many invertebrates and are almost completely reliant upon ad-hoc recording by a network of recorders of differing ability. This network is extremely reliant upon a small nucleus of specialists who assist with identification and record verification on a voluntary basis.

There have been three attempts to develop red lists for Britain’s hoverflies. Each has been substantially reliant upon data supplied by volunteer recorders. Each attempt has worked with the best available evidence. The most recent study (Ball & Morris, 2014) was greatly assisted by the level of refinement that has arisen from comprehensive assembly of data and efforts to make sure that broad-scale geographic coverage has been achieved. The comparative tables in that report show how, in successive reviews, the numbers of species accepted as meeting the threat criteria have dropped. Although the number of species that are red-listed might be expected to have dropped because the criteria have been refined, the numbers meeting the Nationally Scarce category have dropped sharply because we now have a vastly improved understanding of species’ distribution and abundance. This would not have been possible without a network of volunteer recorders.

Although most of Britain's biodiversity data come from voluntary recording network, it is still far better than exists in almost any other country. In the case of hoverflies, The Netherlands, Germany and Scandinavia all have active recording networks, but even they lack the coverage that has been achieved in the UK. This is clearly illustrated by the data held on the Global Biodiversity Information Facility (GBIF)1, two examples of which are shown below

1 http://www.gbif.org/

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(Figures 14a & b) (note that some countries such as France and Italy do not place data on GBIF).

14a. Episyrphus balteatus 14b. Eristalis tenax

Figure 14. Distribution maps of two common hoverflies in Europe: Episyrphus balteatus and

Eristalis tenax according to data available from the Global Biodiversity Information Facility (GBIF).

Distribution data and records of rare species from ad-hoc sources are therefore fundamental to wildlife conservation. In addition, provided there are enough records, a lot more can be achieved from data sets, including analysis of changes in phenology and responses to climate change. The most important issues in this respect are the need to maintain or grow recorder effort, to maintain or extend geographical coverage and to make sure that the competency of recorders is understood and, where necessary, improved.

3.6. ‘How can photography advance our knowledge of hoverfly taxonomy?’ Keys that we currently use were constructed using preserved, and often rather old, specimens that have shrunk, faded and become brittle. Although they bear superficial resemblance to the living animal, there are subtle differences in body shape and colouration.

Species such as Eristalinus aeneus and E. sepulchralis (and of course many of the Tabanidae with brightly coloured eyes) illustrate the ways in which dead specimens appear very differently from the living animal: in life they have spectacular, iridescent colours, but this does not survive long after death. Some of these features are usually mentioned in descriptions (if recorders bother to read them!), but others are not. For example, it Melanostoma scalare often has bright pea-green halters, but until detailed studies have been undertaken we cannot be sure that this is a consistent feature. Developing a full photographic record of individual species with associated preserved specimens offers the greatest possibility of recording and documenting the appearance of the animals in life, and possibly identifying features that might aid field identification of species that are otherwise unidentifiable without specimens.

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References

Morris, R.K.A. & Ball, S.G., 2015. Photographic records of Diptera collated in 2014: a preliminary analysis. Unpublished report by the Hoverfly Recording Scheme. http://www.bacoastal.co.uk/Entomology/2015-Photo-report.pdf Accessed 11 January 2016

Ball, S.G. & Morris, R.K.A. 2014. A review of the scarce and threatened flies of Great Britain: Part 9: Syrphidae Species Status 6. Joint Nature Conservation Committee, Peterborough. 132pp. http://jncc.defra.gov.uk/pdf/Review_of_Syrphidae_Final_Web.pdf Accessed 11 January 2016

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Appendix 1. Species list of hoverflies recorded from photographs accessed in 2015

Species Number of records

Species Number of records

Anasimiyia contracta 14 Didea fasciata 27

Anasimyia lineata 20 Doros profuges 2

Baccha elongata 148 Epistrophe diaphana 8

Brachypalpoides lentus 10 Epistrophe eligans 229

Brachypalpus laphriformis 6 Epistrophe grossulariae 177

Caliprobola speciosa 1 Epistrophe melanostoma 3

Callicera aurata 7 Epistrophe nitidicollis 8

Callicera rufa 1 Episyrphus balteatus 2,190

Callicera spinolae 1 Eriozona syrphoides 2

Chalcosyrphus nemorum 29 Eristalinus aeneus 31

Cheilosia albipila 3 Eristalinus sepulchralis 63

Cheilosia bergenstammi 6 Eristalis abusiva 4

Cheilosia caerulescens 11 Eristalis arbustorum 270

Cheilosia fraterna 12 Eristalis horticola 128

Cheilosia grossa 8 Eristalis intricaria 209

Cheilosia illustrata 298 Eristalis nemorum 126

Cheilosia impressa 49 Eristalis pertinax 1,894

Cheilosia pagana 78 Eristalis rupium 6

Cheilosia ranunculi 1 Eristalis similis 1

Cheilosia scutellata 12 Eristalis tenax 1,632

Cheilosia soror 16 Eumerus strigatus 1

Cheilosia variabilis 50 Eupeodes corollae 288

Cheilosia vulpina 3 Eupeodes lapponicus 2

Chrysogaster cemiteriorum 6 Eupeodes latifasciatus 46

Chrysogaster solstitialis 106 Eupeodes luniger 633

Chrysogaster virescens 3 Ferdinandea cuprea 80

Chrysotoxum arcuatum 42 Ferdinandea ruficornis 1

Chrysotoxum bicinctum 166 Helophilus hybridus 60

Chrysotoxum cautum 49 Helophilus pendulus 1,329

Chrysotoxum elegans 8 Helophilus trivittatus 46

Chrysotoxum festivum 126 Lejogaster metallina 3

Chrysotoxum verralli 31 Leucozona glaucia 211

Criorhina asilica 2 Leucozona laternaria 35

Criorhina berberina 24 Leucozona lucorum 190

Criorhina floccosa 18 Mallota cimbiciformis 5

Criorhina ranunculi 9 Melangyna cincta 9

Dasysyrphus albostriatus 138 Melangyna lasiophthalma 20

Dasysyrphus pinastri 5 Melangyna quadrimaculata 2

Dasysyrphus tricinctus 45 Melangyna umbellatarum 28

Dasysyrphus venustus 33 Melanogaster hirtella 3

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Melanostoma mellinum 48 Portevinia maculata 35

Melanostoma scalare 754 Rhingia campestris 495

Meligramma euchromum 4 Rhingia rostrata 59

Meligramma guttatum 6 Riponnensia splendens 48

Meligramma trianguliferum 4 Scaeva pyrastri 353

Meliscaeva auricollis 335 Scaeva selenitica 45

Meliscaeva cinctella 150 Sericomyia superbiens 30

Merodon equestris 479 Sericomyia lappona 18

Microdon analis 2 Sericomyia silentis 381

Myathropa florea 698 Sphaerophoria rueppellii 1

Myolepta dubia 4 Sphaerophoria scipta 369

Neoascia interrupta 1 Sphegina sibirica 15

Neoascia podagrica 15 Syritta pipiens 619

Neoascia tenur 5 Syrphus nitidifrons 1

Orthonevra geniculata 2 Syrphus ribesii 767

Parasyrphus lineola 4 Syrphus torvus 202

Parasyrphus punctulatus 21 Triglyphus primus 1

Parasyrphus vittiger 1 Tropidia scita 52

Parhelophilus frutetorum 4 Volucella bombylans 224

Pelecocera tricincta 1 Volucella inanis 220

Pipiza austriaca 5 Volucella inflata 39

Pipizella viduata 13 Volucella pellucens 395

Platycheirus albimanus 926 Volucella zonaria 333

Platycheirus ambiguus 1 Xanthandrus comtus 23

Platycheirus angustatus 5 Xanthogramma citrofasciatum 17

Platycheirus fulviventris 2 Xanthogramma pedissequum ss. 83

Platycheirus granditarsus 34 Xanthogramma stackelbergi 3

Platycheirus manicatus 74 Xylota jakutorum 17

Platycheirus rosarum 42 Xylota segnis 366

Platycheirus scutatus ss. 3 Xylota sylvarum 66

Platycheirus tarsalis 8 Xylota xanthocnema 2

Pocota personata 3

Aggregated species

Cheilosia albitarsis sl. 127

Melangyna compositarum/labiatarum 42

Microdon mutabilis sl 4

Platycheirus clypeatus sl. 2

Platycheirus peltatus sl. 36

Platycheirus scutatus sl. 112

Xanthogramma pedissequum sl. 98

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Appendix 2. Detailed breakdown of the representation of British hoverfly genera within the 2014 photographic database

Tribe GB Fauna

Species recorded

% GB fauna in sample

Genera Identified records

Unidentified records

Total records

% identified

Bacchini 1 1 100 Baccha 148 0 148 100

3 2 66.67 Melanostoma 802 258 1060 75.66

25 12 48 Platycheirus 1245 595 1840 67.66

1 1 100 Xanthandrus 23 0 23 100

0

Uncertain genus

84 84 N/A

Callicerini

3 3 100 Callicera 9 0 9 100

Cheilosini

38 14 36.84 Cheilosia 674 328 1002 67.27

2 2 100 Ferdinandea 81 0 81 100

1 1 100 Portevinia 35 0 35 100

2 2 100 Rhingia 554 4 558 99.28

Chrysogastrini

4 0 0 Brachyopa 0 4 4 0

3 3 100 Chrysogaster 115 15 130 88.46

1 0 0 Hammerschmidtia 0 0 0 N/A

2 1 50 Lejogaster 3 1 4 75

2 1 50 Melanogaster 3 29 32 9.38

2 1 50 Myolepta 4 0 4 100

6 3 50 Neoascia 21 179 200 10.5

4 1 25 Orthonevra 2 1 3 66.67

1 1 100 Riponnensia 48 0 48 100

4 1 25 Sphegina 15 40 55 27.27

0

Uncertain genus

10 10 N/A

Eristalini

5 1 20 Anasimyia 34 17 51 66.67

2 2 100 Eristalinus 94 7 101 93.07

10 9 90 Eristalis 4270 497 4767 89.57

5 3 60 Helophilus 1435 32 1467 97.82

1 0 0 Lejops 0 0 0 N/A

1 1 100 Mallota 5 0 5 100

1 1 100 Myathropa 698 0 698 100

3 1 33.33 Parhelophilus 4 106 110 3.64

Uncertain genus

1 1 N/A

Merodontini

5 1 20 Eumerus 1 77 78 1.28

1 1 100 Merodon 479 0 479 100

1 0 0 Psilota 0 0 0 N/A

Paragini

4 0 0 Paragus 0 12 12 0

Pelecocerini

3 1 33.33 Pelecocera 1 0 1 100

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Pipizini

7 0 0 Heringia 0 16 16 0

7 1 14.29 Pipiza sp. 5 45 50 10

3 1 33.33 Pipizella 13 33 46 28.26

2 0 0 Trichopsomyia 0 0 0 N/A

1 1 100 Triglyphus 1 0 1 100

0 Uncertain genus 16 16 N/A

Sericomyiini

3 3 100 Sericomyia 429 0 429 100

Syrphini

8 6 75 Chrysotoxum 422 13 435 97.01

7 4 57.15 Dasysyrphus 221 38 259 85.33

3 1 33.33 Didea 27 5 32 84.38

1 1 100 Doros 2 0 2 100

6 5 83.33 Epistrophe 425 5 430 98.84

1 1 100 Episyrphus 2190 0 2190 100

1 1 100 Eriozona 2 0 2 100

9 4 44.44 Eupeodes 969 424 1393 69.56

3 3 100 Leucozona 436 0 436 100

9 5 55.56 Melangyna 101 34 135 74.81

1 0 0 Megasyrphus 0 0 0 N/A

3 3 100 Meligramma 14 0 14 100

2 2 100 Meliscaeva 485 2 487 99.59

6 3 50 Parasyrphus 26 5 31 83.87

5 2 40 Scaeva 398 6 404 98.51

11 2 18.18 Sphaerophoria 370 579 949 38.99

5 3 60 Syrphus 970 1704 2674 36.28

3 3 100 Xanthogramma 201 1 202 99.51

0 Uncertain genus 85 85 N/A

Volucellini

5 5 100 Volucella 1211 8 1219 99.34

Xylotini

1 0 0 Blera 0 0 0 N/A

1 1 100 Brachypalpoides 10 0 10 100

1 1 100 Brachypalpus 6 0 6 100

1 1 100 Caliprobola 1 0 1 100

2 1 50 Chalcosyrphus 29 0 29 100

4 4 100 Criorhina 53 2 55 96.36

1 1 100 Pocota 3 0 3 100

1 1 100 Syritta 619 0 619 100

1 1 100 Tropidia 52 0 52 100

7 4 57.15 Xylota 451 15 466 96.78

Uncertain genus 0 N/A

Microdontinae

4 2 50 Microdon 6 2 8 75