Nottinghamshire Glow Worms 2023
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The Glow Worm is without doubt, one of our most fascinating insects. Famous for the ability to produce its own light, the green bioluminescence emitted by the female Glow Worm has formed the basis of countless fairy tales and folklore over centuries.

Although still regarded by some authorities as being both nationally and locally common, this delightful beetle has been proved to be in serious decline in Nottinghamshire.

The data collected by a number of recorders over the past ten years, has helped confirm both a decline and a demise in Nottinghamshire's Glow Worm populations. However, getting people to sit up and take notice has proved to be rather difficult and it doesn't help when those very same authorities continue to denounce any existance of decline. 

Habitat loss through urbanisation and industrial development, the use of pesticides and herbicides in modern farming practices and the increase in light pollution, are all thought to have contributed to the Glow Worm's decline.

 
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But Nottinghamshire is fortunate in having one of the UK's largest and most famous Glow Worm colonies in the shape of Clipstone Old Quarter. For many years, Clipstone Old Quarter (located within the heart of Sherwood Forest) was synonymous for almost producing large Glow Worm numbers over a season, but quite often the UK's earliest records of both larvae and females. And as we enter yet another year, there is much to look forward to, despite a recent fall in Glow Worm numbers.
 

Help monitor Glow Worm distribution - contribute your records

Members of the public can contribute to the Nottinghamshire Glow Worm Survey and we welcome any Glow Worm records from within VC56 Nottinghamshire. The easiest way to contribute your records, is by completing the simple online survey form on the right.

The form can also be used to send in any old Glow Worm records you may have, as old records are important in helping to determine a more accurate picture of Glow Worm distribution and how it has changed over time. And it is just as useful if we know where Glow Worms are not found, so please remember that negative results from a site are equally as important as positive results and will help our mapping of the Glow Worm's distribution.

Useful Glow Worm links on www.eakringbirds.com

 
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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.

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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