Nottinghamshire Glow Worms 2023 |
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Predicting the start of the
2023 season I occasionally still get asked to predict the date when the first Glow Worm will appear at Clipstone Old Quarter each year? It's a difficult question to answer with any degree of accuracy, although people expect it to be easy after monitoring this famous Glow Worm colony for well over a decade. Such predictions are difficult and will always be largely guesswork at best, as there are a number of factors needed to be taken into account and they vary from year to year. Temperature over preceding months, or over the previous year is certainly one and unsympathetic habitat management, or the success of larvae finding food are others. |
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Periods of prolonged snow, ice or heavy rain, drought and high temperatures are other factors which can affect larval and pupal development. The hot, dry summer of 2022 may well prove to have had serious implications on many Glow Worm populations across much of the UK and so counts at some sites affected by the dry conditions may well be down on recent years. In Nottinghamshire, those Glow Worm colonies situated on areas of heathland will likely be the most affected, although this remains to be seen. The Sherwood Forest area has undergone periods of very dry conditions in previous years, which, if they continued for any length of time, were showed through observations to lead to the dehydration of a large number of larvae. During larval surveying in the late Summer and early Autumn of 2013 (another very dry Summer) Dilys and I found some larvae were becoming paper thin through dehydration and when rain eventually arrived on September 6th, we recorded larvae taking on much needed water. The summer of 2022 though, was on another level in comparison to what I have personally witnessed at Sherwood Forest previously. The variabilities of the UK weather is without doubt the biggest factor in determining when any species will appear, but it's not just the weather or conditions around the time of adult emergence, but over the course of the previous few months and probably well over the past year that needs to be borne in mind. |
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Photograph by Martin Dale |
For larvae going on to become adult this Spring and Summer, it is necessary for those larvae to have had suitable conditions for hunting and to have managed to find enough food over the previous Summer and Autumn and that is probably be more critical than the immediate Spring period. We always thought that most pre-pupation development took place place prior to over-wintering and in captivity, we certainly had over-wintering larvae never eat anything before pupation. |
Average monthly minimum Winter temperatures 2008-2023 | ||||||||||||||||
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2008/09 | 2009/10 | 2010/11 | 2011/12 | 2012/13 | 2013/14 | 2014/15 | 2015/16 | 2016/17 | 2017/18 | 2018/19 | 2019/20 | 2020/21 | 2021/22 | 2022/23 | ||
Nov - Apr | 2.80°C | 2.08°C | 2.35°C | 3.28°C | 1.55°C | 3.33°C | 2.93°C | 3.59°C | 3.46°C | 2.68°C | 2.97°C | 3.50°C | 2.55°C | 3.61°C | N/A | |
Jan - Apr | 2.80°C | 1.62°C | 3.67°C | 2.75°C | 1.05°C | 3.62°C | 2.45°C | 2.35°C | 3.50°C | 2.47°C | 3.41°C | 3.82°C | 1.92°C | 3.40°C | N/A | |
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Date of first female | May 27th | May 24th | May 13th | May 30th | June 8th | May 18th | May 23rd | June 3rd | May 20th | May 24th | May 31st | May 20th | June 3rd | May 17th | N/A | |
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Average monthly maximum Winter temperatures 2008-2023 | ||||||||||||||||
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2008/09 | 2009/10 | 2010/11 | 2011/12 | 2012/13 | 2013/14 | 2014/15 | 2015/16 | 2016/17 | 2017/18 | 2018/19 | 2019/20 | 2020/21 | 2021/22 | 2022/23 | ||
Nov - Apr | 8.68°C | 8.04°C | 8.71°C | 9.79°C | 7.33°C | 10.29°C | 9.50°C | 10.26°C | 9.60°C | 8.51°C | 10.51°C | 10.31°C | 8.91°C | 10.41°C | N/A | |
Jan - Apr | 9.27°C | 7.67°C | 10.70°C | 9.75°C | 6.95°C | 10.89°C | 9.60°C | 9.30°C | 10.12°C | 8.57°C | 10.85°C | 11.30°C | 8.80°C | 10.90°C | N/A | |
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Date of first female | May 27th | May 24th | May 13th | May 30th | June 8th | May 18th | May 23rd | June 3rd | May 20th | May 24th | May 31st | May 20th | June 3rd | May 17th | N/A |
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Nottinghamshire Glow Worm
records 2023 Latest available survey results will appear here from March onwards. |
Surveyed | Site name | Grid ref | Site type/habitat | Qty | Notes | Recorder | ||||||
July 5th | Clipstone Old Quarter | SK608674 | Former Pine plantation and grass/scrub strip | 4 | The first report for several days. Four females recorded this evening, present along Sections I and S. | IB. CC. | ||||||
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Larval survey data
2009-2023 Data gained from larval surveys conducted at Clipstone Old Quarter during March, April and May in previous years, showed a general decrease in the average length of Glow Worm larvae over the time period, but there may be a slight indication of something of an increase since 2021, although this is derived from a much smaller data sample (number of larvae) in both years. We found that the average larval size from 2009 to 2014 was 20.32mm, based on the data gathered from a total of 771 larvae. The data also showed that larvae were on average, considerably larger in 2009 (22.21mm) than in any of the following years, equating to 1.89mm larger than the average produced between 2009 and 2014. This has continued to be the case and the average length of larvae in 2016 was found to be just 17.99mm, showing a decrease of 4.22mm on larval length data obtained in 2009. The data in the table provided in Fig 02 below, is presented as (for example) 17.00mm/tL6. An explanation of this would be 17.00mm (the average larval length) / tL6 (taken from a total of six larvae) but this obviously changes daily after each survey, as the size data for latest weekly time period is continually recalculated and updated. The Spring average follows the same principle, but the average is obviously taken from the total number of larvae found that Spring period. |
Fig 02. ... Glow Worm larval averages during Spring 2009-2023 Data correct as of 01/01/23 * means weekly average data incomplete | |||||||||||||
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Week/period | . | 2009 | 2010 | 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2020 | 2021 | 2022 | 2023 |
March 22-31 | . | ..... | ..... | 18.03mm/tL27 | 21.16mm/tL6. | ..... | 17.90mm/tL13 | . | 18.44mm/tL90 | 17.63mm/tL28 | 00m..............m | 00m.............. | |
April 1-7 | . | 23.33mm/tL3. | 21.27mm/tL13 | 18.64mm/tL70 | 19.00mm/tL5. | .... | 18.65mm/tL24 | 18.16mm/tL6. | 16.46mm/tL13 | 19.75mm/tL4 | 16.75mm/tL4 | ||
April 8-14 | . | 21.14mm/tL14 | 19.58mm/tL17 | 19.19mm/tL31 | 19.66mm/tL9. | 17.11mm/tL9. | 18.27mm/tL59 | 19.11mm/tL16 | 15.00mm/tL3 | 19.71mm/tL7 | |||
April 15-21 | . | 20.45mm/tL10 | 20.78mm/tL18 | 19.78mm/tL53 | 23.20mm/tL5. | 18.34mm/tL34 | 18.62mm/tL22 | 20.66mm/tL8. | 18.26mm/tL20 | 18.00mm/tL1 | |||
April 22-29 | . | 23.32mm/tL25 | 18.74mm/tL53 | 19.97mm/tL39 | 18.77mm/tL9. | 18.61mm/tL25 | 20.20mm/tL36 | . | 18.83mm/tL6* | 21.66mm/tL3 | 21.27mm/tL11 | ||
April 30-May 6 | . | 22.95mm/tL20 | 23.20mm/tL5. | 21.87mm/tL8. | 20.95mm/tL22 | 19.85mm/tL16 | 21.87mm/tL21 | . | 17.66mm/tL15 | . | 19.75mm/tL4 | 21.10mm/tL10 | |
May 7-14 | . | 22.08mm/tL17 | 23.25mm/tL4. | ..... | 22.30mm/tL10 | 21.62mm/tL21 | 21.25mm/tL4. | ..... | 18.22mm/tL22 | ..... | 19.75mm/tL4 | .21.33mm/tL30 | |
May 15-22 | . | . | 19.66mm/tL60 | . | . | 21.71mmtL/8 | . | . | 19.97mm/tL34 | . | . | . | |
May 23-30 | . | . | . | . | . | . | . | 19.11mm/tL90 | . | .. | . | ||
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Spring avg | 22.21mm/tL89 | 20.92mm/tL116 | 19.58mm/tL228 | 20.45mm/tL66 | 19.52mm/tL103 | 19.53mm/tL169 | N/A | 17.99mm/tL83 | N/A | 19.35mm/tL44 | 20.03mm/tL35 |
The size data produced since 2010 has been remarkably consistant where sufficient data was collected, showing a variation of just 1.40mm. 2021 and 2022 data is currently not included in this as the data sample is regarded as being too low in comparison to those years. Breaking the data down further, the average size variation in three of the years since (2011, 2013 and 2014) showed variation as little as 0.06mm. If we exclude the 2009 size data on the basis of being unusually large, then an average larval size at this site would be approximately 20.00mm. The relative consistant larval sizes suggests that variations in rainfall and temperature between November and March in any year, actually had no influence on larval size. |
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