Recent records of the Harvestman Leiobunum sp. A from Worksop Priory
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Due to some five years surveying the growing population of Leiobunum sp A on the walls of Worksop Priory, we felt that a separate page giving the resulting counts and observational notes was needed.

A brief background history

In October 2009, we found a very dark, extremely long-legged Leiobunum type Harvestman on the wall of a Worksop house, which immediately stood out as being very different from any other Harvestman we had seen before.

The Harvestman was found resting on a shady, north-west facing wall in the rear garden of the property, in a quite open position relative to the Ivy growing up the same wall. It was collected and taken home for photographing before being released.

 
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In November 2011, a possible breakthrough came whilst searching for images of Platybunus pinetorum, a recent addition to the UK species list discovered by Paul Richards at Sheffield in June 2010. Images found during a Google search for the similar looking (to the Worksop specimen) Leiobunum tisciae, turned up images of an invasive and unknown Leiobunum found in parts Germany, Switzerland, The Netherlands and Austria. Further research quickly led us to the excellent paper "An unidentified harvestman Leiobunum sp. alarmingly invading Europe" (Arachnida: Opiliones) by Hay Wijnhoven, Axel L. Schönhofer & Jochen Martens and published in December 2007.

One particular image of a male in the paper, seemed to match the Worksop specimen perfectly, so we emailed images of the Worksop specimen to Jochen Martens and Paul Richards for possible identification and confirmation. Both replied back with the conclusion that it was indeed Leiobunum sp. The Harvestmen still (February 2017) remains scientifically un-named.

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2012 records

Following the end of our three year wait to record Leiobunum sp. A again on October 13th 2012, we eventually went on to record a total of 13 males and nine females along the southern wall of the Priory. All the Leiobunum sp. A we found were found resting more or less at eye level, with only one female found about 20 feet up. They clearly preferred the vertical joints or tight recesses built along the southern side of the Priory walls. We made immediate follow-up visits the next day, recording a total of 20 individuals, before a final visit of the year on October 17th, recording a total of 18.

2013 records

Numbers increased on those initially found 2012, with counts of 37 on August 15th, rising to 43 on September 9th. Most of both these counts, were found in two aggregations, usually situated under some degree of shelter via the building's stonework, with up to 27 on the south side of the Priory and 11 under an arch on the eastern side. A count of 46 made on September 22nd, was the highest count to date.

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2014 records

We made two visits to the site and immediately found a single aggregation of 81 Leiobunum sp. A, a few minutes into our search on August 9th 2014. The final total of 202, showed that there had been an enormous increase in numbers from 2013, possibly helped by the exceptionally mild Winter. Similar daytime roost sites, were used as in previous years, but we did note a substantial increase in numbers on the north (shaded) side of Worksop Priory.

Our second visit was made nearly a month later on September 7th and counts had increased to 274. There were increased numbers of Leiobunum sp. A recorded within all aggregations found on our first visit. The aggregation of 81 had grown to 95 and there were several other aggregations which totalled well over 30 individuals.

 
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2015 records

Our first visit of 2015 took place on August 2nd, which was a week earlier than in 2014. A total of 217 Leiobunum sp. A were counted, with many still immature, although there were already a few mature males present. Once again, the main aggregations were located in exactly the same positions on the Priory walls, as recorded in previous years. The largest single aggregation consisted of approximately 90 individuals, but higher than normal numbers were present on the eastern (recorded for the first time on the new section of the Priory) and the northern side. One immature male, was even found underneath the overhanging top stone of a grave and away from the main Priory walls.

Our second visit took place on August 15th. A total count of 212 was made, with groups in similar positions and there was an increase in the numbers of small groups. One usually guaranteed aggregation under an arch on the eastern-end of the Priory had disappeared.

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  We returned to Worksop again on September 4th, noting changes to the distribution of Leiobunum sp. A on the north side of the Priory and actually finding very few to be present. Most were found on the warmer southern walls, probably moving as a result of the recent spell of cold northerly winds. A final total of 159 was disappointing, but a check of an adjacent stone building proved worthwhile, with a further 54 Leiobunum sp. A recorded. Final total for the visit was 213, so amazingly similar counts for all three visits this year so far.

On September 14th, we returned with wildlife cameraman James Dunbar to conduct another count. On arrival we immediately checked the first aggregation, which only a few weeks ago had held approximately 90 individuals. With the division of this aggregation noted on our previous visit, we noted a further reduction in numbers and after checking all the southern walls of the Priory, concluded that many Leiobunum sp. A had dispersed further afield, including one group which had aggregated on the north side of a large tomb.

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No Leiobunum sp. A were found to be present on the Priory's eastern side and there were very few recorded along the northern side. Clearly there was a large reduction in numbers and possibly a more widespread dispersal away from the Priory. A total of 116 Leiobunum sp. A were found on the Priory and another 28 on an adjacent building, which had reduced in number from 54 on our previous visit.

On October 8th, we visited Worksop Priory to conduct another survey. Since our last visit, the weather had been largely fine and dry with some pleasantly warm daytime temperatures, but very cool nights. What remained of any of the aggregations present on September 14th, had dispersed and most of the 34 Leiobunum sp. A recorded were found well distributed over the walls of the Priory and with very few on the Priory's north side.

Our latest ever visit to Worksop Priory took place on November 1st. The day was pleasantly warm and sunny and a total of 31 Leiobunum sp. A (19m and 12f) were counted. There had been further movement/spread across the walls of the Priory, although none were present on the shaded north side. It was obvious that the remaining population had moved to the warmer southern and western walls and many Leiobunum sp. A were quite openly sat in full view. All were recorded singly or in twos, but not male with female. Most specimens had darkened further (especially the males) which we were surprised to find, now out-numbered females by almost two to one. Additional surveys for Leiobunum sp. A at other Worksop locations proved negative.

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We continue to be convinced that there are other sites in Worksop for Leiobunum sp. A, but have had no success so far. The housing estate where we first recorded this Harvestman back in 2009, was also surveyed again in 2015.

2016 records

A much earlier visit was made to Worksop Priory, with the intention being to search for juvenile Leiobunum sp.A, which we thought would be low on the Priory walls by the middle of June. Our visit was on June 17th and we found most of the 85 Leiobunum sp. A as sub-adults, but we did record a few juveniles (shown right) of just 2.5mm body length.

There were no aggregations, but we did locate a loose group of eight sub-adults on the south wall of the Priory. None of the traditional aggregation areas on the Priory walls were occupied and most of the Leiobunum sp A found, were well scattered across the whole of the Priory's southern walls, usually in cracks and crevices, but often openly on the stonework in the manner of our native Leiobunum species.

 
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Our second visit to Worksop Priory ended up being slightly later than we would have wished, but numbers had substantially increased and approximately 223 Leiobunum sp. A were counted on July 31st. Aggregations had again formed in the exact same locations on the walls of the Priory and on an adjacent stone building, as have been used in previous years. The largest single aggregation totalled 94 individuals.

Some two weeks into August and we visited Worksop again and found a record count of 308 Leibunum sp. A, on the Priory walls. The aggregation of 94 individuals on July 31st, had now risen to an impressive 130 by August 13th. This high count failed to increase (or even last) and by the time we conducted or next survey on September 10th, it was clear that the aggregations had broken up into considerably smaller groups. The largest group we found was just 24 and unusually, not in any of the traditional locations. A total of 146 Leibunum sp. A for the visit seemed small.

Below are our visit dates and counts of the Leiobunum sp A population at Worksop Priory since 2012. The small graph depicts the highest count per year, reading from 2012 on the left.

2012 2013 2014 2015 2016
13/10/12 ....T22 15/08/13 ... T37 09/08/14 ... T202 02/08/15 ... T217 17/06/16 ... T85
14/10/12 ... T20 24/08/13 ... T38 07/09/14 ... T274 15/08/15 ... T212 31/07/16 ... T223
17/10/12 ... T18 07/09/13 ... T43 ... 06/09/15 ... T213 13/08/16 ... T308
... 22/09/13 ... T46 ... 14/09/15 ... T144 10/09/16 ... T146
... ... ... 08/10/15 ... T34 30/09/16 ... T63
... ... ... 01/11/15 ... T31 16/10/16 ... T41
... ... ... ... ...
 
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Late Summer and early Autumn visits took place on September 30th, producing a total of 63 Leibunum sp A, and then on October 16th, when the count had lowered again to 41. Approximately 27 of the 41 total were males and the 14 females were mostly well scattered along the southern and northern walls of the Priory.
 
The discovery of Leiobunum sp. A at Worksop in 2009
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