|Recent records of the Harvestman Leiobunum sp. A from Worksop Priory|
|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
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.
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.
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.
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.
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.
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.
|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
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.
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
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.
|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.
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.
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
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.
|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.|