Nottinghamshire Glow Worms 2021
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The aim of the NGWS is to provide useful data on this decling species. Click the banner for information and how to contribute to the survey
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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.

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

The data collected by a number of local recorders over the past ten years, has helped confirm both decline and 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 deep within the heart of Sherwood Forest) was synonymous for producing the UK's earliest larvae and females and with the 2021 season now underway, following a 21mm larva appearing on March 9th, there is much to look forward to over the next few months.
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Nottinghamshire Glow Worm records 2021
All those records contributed to the Nottinghamshire Glow Worm Survey 2021 will be published both here and on the NGWS page.
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Contributors to the survey 2021:
Many thanks go to all of the following people who have sent in their survey results so far. Trevor Pendleton.
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Surveyed   Site name   Grid ref   Site type/habitat   Qty   Notes   Recorder
April 20th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   1   A single 18mm larva found dead this evening   TP.
April 18th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   0   No larvae recorded   TP.
April 4th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   1   A single 20mm larva found this evening   TP.
April 3rd   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   1   Cool conditions at present, so it was surprising to find a 19mm larva, which was extremely emaciated, so has been temporarily taken into care   TP.
April 1st   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   2   Two (dead) 20mm larvae found this evening, including one unusually again in Section A.   TP.
March 31st   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   4   Four larvae recorded with larval lengths of 18mm x2, 20mm and 22mm.   TP.
March 30th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   7   Seven larvae recorded in good conditions this evening, but unfortunately one was found freshly dead. Larval lengths included singles measuring 16mm, 17mm, 18mm and two at 14mm and two at 19mm   TP.
March 29th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   1   A single 19mm larva found this evening   TP.
March 28th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   4   A total of four larvae recorded this evening, with one unfortunately found dead measuring 18mm. The three live larva included lengths of 15mm, 18mm and 21mm   TP.
March 26th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   1   A single 22mm larva found fatally injured   TP.
March 25th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   1   A single 15mm larva found dead   TP.
March 24th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   2   Two larvae (14mm and 22mm) found in Sections B and D respectively this evening   TP.
March 22nd   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   2   Two larvae found this evening, including a 15mm larva in Section A (unusually) and a 14mm larva in Section D   TP.
March 21st   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   0   No larvae recorded   TP.
March 20th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   0   No larvae recorded   TP.
March 18th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   3   Three larva recorded today, with a 15mm larva, a 24mm larva (both alive) and a dead larva measuring 19mm   TP.
March 17th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   1   A single 13mm larva found dead this afternoon   TP.
March 16th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   1   A single 14mm larva found dead this afternoon   TP.
March 13th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   0   No larvae recorded   TP.
March 9th   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   1   A single 21mm larva found active mid-afternoon   TP.
February 23rd   Clipstone Old Quarter   SK608674   Former Pine plantation and grass/scrub strip   0   No larvae recorded   TP.
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Larval survey data, counts and a high mortality rate

Almost year on year, surveying for Glow Worm larvae during March, April and into May, has showed a decrease in the average length of Glow Worm larva at Clipstone Old Quarter since 2009. Larval measuring techniques have remained unchanged through the years and the resulting size data is totally accurate.
 
  The data for March 2021 showed in Figure 1 has been a gradual process of adding and building the data obtained over 15 late afternoon/evening surveys and as the data for April comes in, that will see a continual change throughout the month. Eventually the data for each weekly period is added to the table in Figure 03 and a direct comparison can be made with the same week in previous years.

2021 has seen an unusually high mortality rate for Glow Worm larvae. To date (April 1st) some 9/30 larvae had been killed by the increase in footfall and cycles through Sections A,B,C and D. That equates to virtually a third of larvae found and in most years nine dead larvae would equate to the combined total dead for a complete Spring period out of around 100 larvae.

While the effects of lockdowns as a result of Covid-19 has led to a greater increase in public use of the site, the blame has to be laid firmly at the door of the site owners/managers etc, who's non commitment to Clipstone Old Quarter as part of the Birklands West and Ollerton Corner SSSI, has mean that the Sustrans path is (for most of its length here) now 30-50% the width it was originally. Less path means public use and larval use is more concentrated and the two obviously clash, but there are moves to restore the site to how it was a decade or so ago.
 
Fig 01. ... Diurnal Glow Worm larval size ranges found during March 2021  Data correct as of 31/03/21
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    9mm-15mm larval size range   Intermediate   19mm-28mm larval size range
Section   9mm 10mm 11mm 12mm 13mm 14mm 15mm   16mm 17mm 18mm   19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. 1 0 0 1 0 0 1 .. 0 0 0 .. 0 0 0 0 0 0 0 0 0 0
B .. 0 0 0 0 0 1 1 .. 1 0 2 .. 2 0 0 1 0 1 0 0 0 0
C .. 0 0 0 0 0 1 0 .. 0 0 0 .. 0 0 0 1 0 0 0 0 0 0
D .. 0 0 0 0 1 3 2 .. 0 1 3 .. 2 1 2 1 0 0 1 0 0 0
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    9mm-15mm larval size range 35.70%   Intermediate 25.00%   19mm-28mm larval size range 39.30%
Total % .. 0.00 0.00 0.00 0.00 3.57 17.85 14.28 ... 3.57 3.57 17.85 ... 14.28 3.57 7.14 10.71 0.00 3.57 0.00 0.00 0.00 0.00
 
Fig 02. ... Diurnal Glow Worm larval size ranges found during April 2021  Data correct as of 20/04/21
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    9mm-15mm larval size range   Intermediate   19mm-28mm larval size range
Section   9mm 10mm 11mm 12mm 13mm 14mm 15mm   16mm 17mm 18mm   19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. 1 0 0 1 0 0 1 .. 0 0 0 .. 0 1 0 0 0 0 0 0 0 0
B .. 0 0 0 0 0 1 1 .. 1 0 1 .. 2 1 0 0 0 1 0 0 0 0
C .. 0 0 0 0 0 1 0 .. 0 0 0 .. 0 0 0 1 0 0 0 0 0 0
D .. 0 0 0 0 1 3 2 .. 0 1 1 .. 1 1 2 1 0 0 1 0 0 0
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    9mm-15mm larval size range 00.00%   Intermediate 20.00%   19mm-28mm larval size range 60.00%
Total % .. 0.00 0.00 0.00 0.00 0.00 0.00 0.00 ... 0.00 0.00 20.00 ... 20.00 60.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
 
We found that the average larval size from Spring 2009 to 2014 was 20.32mm, based on the data gathered from a total of 771 larvae. It also showed that larvae were considerably larger on average in 2009 (22.21mm) than in any of the following years, equating to 1.89mm larger than the average produced between 2010 and 2015. 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.

The data in the table provided in Fig 03, is presented as 17.00mm/tL6 for example. 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. The Spring average follows the same principle, but the average is obviously taken from the total larvae found that particular Spring.
 
Fig 03. ... Glow Worm larval averages during Spring 2009-2021  Data correct as of 20/04/21
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Week/period . 2009 2010 2011 2012 2013 2014 2015 2016 2020 2021
March 22-31 . ..... ..... 18.03mm/tL27 21.16mm/tL6. ..... 17.90mm/tL13 .   18.44mm/tL90 17.63mm/tL28
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
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    
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  
April 22-29 . 23.32mm/tL25 18.74mm/tL53 19.97mm/tL39 18.77mm/tL9. 18.61mm/tL25 20.20mm/tL36 .   18.83mm/tL6* 18.00mm/tL1
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 .  
May 7-14 . 22.08mm/tL17 23.25mm/tL4. ..... 22.30mm/tL10 21.62mm/tL21 21.25mm/tL4. . 18.22mm/tL22    
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 N/A

 

 

The size data produced since 2010 has been remarkably consistant, showing a variation of just 1.40mm. 2021 data is not included in this. 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 to us that variations in rainfall and temperature between November and March in any year, actually had no influence on larval size.
 
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