The size variation and age ratios found within the larval population of the Glow Worm (Lampyris noctiluca) during Autumn
.Project 2: Phase 1. 2012 results
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Please quote the following when referencing this document

Pendleton, T.A.. Pendleton, D.T. and Dale, M. "The size variation and age ratios found within the larval population of the Glow Worm (Lampyris noctiluca) during Autumn" www.eakringbirds.com; December 2012.

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  The general nature of research is that, a) you first have your theory, b) you then have to confirm your theory and finally c) you have to produce the evidence to show how you proved your theory! So in August 2012, following the end of another adult glowing season, we decided to engage in two research projects, both of which are directly linked in many ways.

It was anticipated at the outset, that both projects would probably take several years to complete before enough data had been collected and from which any firm conclusions could be derived.

But our Project 2: Phase 1. 2012 research has already yielded some interesting results and we feel that we are already making progress towards finding the answers to some of our questions. This page details our current findings.

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Project 2: Phase 1. 2012 ... Table of contents
 
1.0 ... Introduction to Project 2: Phase 1. 2012
........ 1.1 ... Recording methodology and data collection
........ 1.2 ... A brief overview of the study colony history
........ 1.3 ... Assigning ages to larvae
........ 1.4 ... Intermediate age range larvae
........ 1.5 ... The effects of annual rainfall and temperature on larval size and over-wintering success
........ 1.6 ... Site map and survey sections
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2.0 ... Summary and review of larval size range data from Spring 2009 - 2012
........ 2.1 ... Spring 2009 larval sizes
........ 2.2 ... Spring 2010 larval sizes
........ 2.3 ... Spring 2011 larval sizes
........ 2.4 ... Spring 2012 larval sizes
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3.0 ... Larval activity and bioluminescence during the late Summer and Autumn
........ 3.1 .... Autumn 2012 larval size data
........ 3.2 ... On site larval distribution and hunting range
........ 3.3 ... Larval activity and bioluminescence
........ 3.4 ... Larval activity in relation to ground temperatures
........ 3.5 ... 1cy and 2cy population levels
........ 3.6 ... Mortality rates within the larval population
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4.0 ... Proposed research work for Project 2: Phase 2. 2013
 
 
1.0 ... Introduction to Project 2: Phase 1. 2012

Project 2: Phase 1. 2012 was conducted by Trevor and Dilys Pendleton (TDP), based at Market Warsop, Nottinghamshire. We were also assisted by Martin Dale (MD) based in Nottingham, who assisted us with field survey work and also provided important comparison data based on observations of captive larvae. Martin is also co-author and researcher of Project 1: Phase 1. 2012 "Some notes and observations on the bioluminescence exhibited by the larva of the Glow Worm (Lampyris noctiluca) in captivity".

Our original focus for our Project 2: Phase 1. 2012 research, was to collate as much larval size range data from our study colony at Clipstone Old Quarter in Sherwood Forest during the late Summer and Autumn of 2012. But at a fairly early stage, it was decided that the research would be considerably more useful, if it was extended to cover at least one complete year and also researched other aspects of larval activity.

We decided that the primary aims of this research were to try and accurately determine the following aspects of Glow Worm larval activity.

  • The number of active larvae present during the latter months of the year (post adult glowing season)
  • The period of larval activity during the Autumn and early Winter months
  • Peak time for greatest larval activity
  • The range of larval sizes present on site
  • The usual hunting range of larvae in relation to forest paths and tracks
  • Activity of larvae in relation to ground temperature

1.1 ... Recording methodology and data collection

Recording larvae in the wild is time consuming, sometimes with little success for the number of hours spent in the field collecting data. The amount of success was largely dependent on the time of the year, with August and September providing the best results in terms of the amount of larvae recorded and data collected. Temperature also proved to be an important factor and site visits in late Autumn were confined to cloudy or moonless nights wherever possible and ideally when the temperature was 8C or above. Clear nights with a near full moon provided very limited success.

The process of surveying for larvae was simple, with the observers walking slowly along forest paths and tracks until the bioluminescent glow of a larva was seen. The larva would be located with the aid of torchlight and its length measured, before being returned to the place of capture. Other similar larval measuring techniques adopted by other researchers, have involved measuring the width of the larva rather than length, but we are satisfied that our measuring techniques are accurate after measuring over 450 larvae during the course of four successive Springs and over 150 in Autumn 2012 and that the data is true.

1.2 ... A brief overview of the study colony history

The study colony at Clipstone Old Quarter is situated within Sherwood Forest in Nottinghamshire and although assigned SSSI status, the site does not fall within the Sherwood Forest National Nature Reserve boundary.

We have actively studied the number of adult female Glow Worms at this colony since 2008, but intensified our coverage in 2009 and have not missed a visit during the adult glowing season since. Coupled with our Spring larval surveying, we have accumulated well over 500 evenings worth of larval and adult data, probably making this the most intensely studied and recorded Glow Worm colony in the UK.

Despite being located in the middle of Nottinghamshire, this colony has proved to be one of the earliest UK sites for Glow Worms. We believe that this is down to observer coverage rather than females appearing genuinely early, as the site does not seem to have a particularly warm climate. Another interesting aspect of the site is the consistantly high numbers of female Glow Worms recorded each year (see Table 01) producing a total of 2,278 females between 2009 and 2012 and has yet to produce the occasional poor year often recorded at other UK sites.

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The fact that the adult Glow Worm population at Clipstone Old Quarter has done so well each year is especially interesting, considering that one other Glow Worm colony at nearby Sherwood Heath SSSI, has seen a considerable decrease in the number of adults present over the same time period.

Counts of over 200 females in 2008, have recently dropped down to just single females in 2010, 2011 and 2012, while three other nearby colonies are also struggling to survive with very small numbers of females annually.

 
Table 01. Female totals 2009-2012
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Year   Total
2009 .... 385 females
2010 .... 502 females
2011 .... 792 females
2012 .... 599 females
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There are several factors that could have influenced the decline in Glow Worm numbers at Sherwood Heath SSSI, including dryness of habitat during the Summer, subsequent lack of available prey items and the use of herbicides to control Bracken spread using heavy machinery. Clipstone Old Quarter has so far escaped the use of chemical sprays and is generally less susceptible to over-drying, being protected from wind and having areas of shade provided by mature Pine plantations and areas of deciduous trees. The site can become dry during periods of exceptionally sunny weather, but any effects have not been visible among the adult Glow Worm population in recent years.

1.3 ... Assigning ages to larvae

Ageing Glow Worm larvae is not a simple process and unless larvae are reared in captivity from egg to adult, then assigning the correct calendar year (cy) to a larva, is somewhat open to conjecture and recorder interpretation and the real difficulty is created by the fact that some Glow Worm larvae almost certainly reach adulthood within 12-14 months, while others could possibly take as long as three years before reaching the pupation stage.

Our data is based on the assumption that most Glow Worm larvae have more or less a two year period of development, or at least over-winter twice. This would mean that larvae found during both Spring and Autumn 2012, would generally originate from eggs laid by females in 2010 and 2011. Hence throughout 2012, 2010 larvae would be in their second calendar year (2cy) and 2011 larvae would be in their first calendar year (1cy).

Of course there are always exceptions to the rule and we have listed three possible examples of larval life cycles below, based over different lengths of larval development.

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  1cy larval cycle     2cy larval cycle     2cy - 3cy larval cycle
1. A mated female lays eggs in late May 2010.   1. A mated female lays eggs in early June 2010.   1. A mated female lays eggs in mid-July 2010.
2. Eggs hatch into 4mm larvae around late June 2010.   2. Eggs hatch into 4mm larvae around late June or mid-July 2010.   2. Eggs hatch around mid/late August into 4mm larvae.
3. Larva feeds well and grows from 4-17mm during Summer of 2010.   3. Larva possibly grows to 7-10mm before over-wintering from 2010/2011.   3. Larva feeds and grows, reaching 6-7mm before over-wintering from 2010/2011.
4. Larva over-winters once from 2010/2011.   4. Larva grows from 7-10mm - 17-26mm during Summer of 2011.   4. Larva continues to grow during Summer 2011, possibly reaching 15-20mm.
5. Larva completes growth and becomes adult in late July 2011.   5. Larva over-winters for second time from 2011/2012.   5. Larva over-winters for second time from 2011-2012.
      6. Larva becomes adult in Spring/Summer 2012.   6. Larva either completes growth and becomes adult in Spring 2013 or
  ...............................................................     ................................................................   7. Continues development and growth before over-wintering for a third time from 2012/2013, becoming adult in Spring 2013.
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1.4 ... Intermediate age range larvae

The charts in the Spring and Autumn larval size sections, show that we have categorised larvae into three groups or age ranges. These are 1cy, 2cy and intermediate. Intermediate larvae are those larvae whose length measurement places them in a grey area between both calendar year groupings. Effectively these larvae could be either well developed 1cy larvae or poorly developed 2cy larvae. Alternatively, they could be 2cy larvae with a third year of growth to complete before pupation. It is possible that intermediate larvae could make up a large proportion of late emerging females we record during the second half of July.

As the total number of females present at our Sherwood Forest study site has yet to be below 385 females in four years of comprehensive study, the evidence (based on female counts) for a two year larval stage for all larvae, has become indeterminable from the number of adult females recorded since 2009. Because larval development is obviously dependant on food, moisture and temperature, larvae that are successful (or fortunate) in prey location will develop at an increased rate, but if the percentage of larvae reaching adulthood within a year is very small, biennial differences in the number of females have clearly taken many decades to reduce.

1.5 ... The effects of annual rainfall and temperature on larval size and over-wintering success

In Table 02 we have looked at the period of April 1st - 7th of each year, taken the average larval sizes found along one stretch of cycle track (sections A, B, C and D on the map) and compared them with the recorded rainfall between the months of April to August & September to March.

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Table 02. .. Average larval sizes and rainfall during Spring 2009 - 2012
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Year Total Rainfall . . Summer period Rainfall . Winter period Rainfall . Survey period Size (Avg)
2007 770.90mm . . Apr 07 - Aug 07 473.50mm . Sep 07 - Mar 08 325.90mm . . .
2008 725.00mm . . Apr 08 - Aug 08 312.80mm . Sep 08 - Mar 09 346.50mm . . .
2009 558.60mm . . Apr 09 - Aug 09 261.30mm . Sep 09 - Mar 10 337.70mm . April 1-7 2009 23.33mm
2010 647.80mm . . Apr 10 - Aug 10 273.80mm . Sep 10 - Mar 11 302.90mm . April 1-7 2010 21.27mm
2011 423.50mm . . Apr 11 - Aug 11 198.80mm . Sep 11 - Mar 12 224.20mm . April 1-7 2011 18.64mm
2012 . . . Apr 12 - Aug 12 444.00mm . Sep 12 - Mar 13 . . April 1-7 2012 19.00mm
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The rainfall is based on Met Office data for Waddington in Lincolnshire, which is the nearest weather station to the Sherwood Forest area that lists historical rainfall data. In the table, we have divided the 12 months into two periods, just to see if the data held up for the preceding Summer, as it seems to do with the preceding Winter. Note that much of the 2012 data is incomplete at the time of writing, but there does seem to be a strong correlation between Spring larval sizes and the amount of rainfall during the preceding months/year based on the data we have available.
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Figure 01. .. The monthly minimum and maximum daytime temperatures 2007 - 2013
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  Obviously, larvae found in Spring 2009, will have passed through at least one very wet 12 month period before reaching the pupation stage.

But larvae found in the Spring of subsequent years, will have had to contend with slightly drier conditions for much of their larval life and that may have contributed to the lower average larval length shown since 2009.

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Larvae are extremely susceptible to dehydration and we have noted clear reductions in the numbers of pre-pupating larva recorded during periods of very dry weather in past years and if dry weather persists well into the Autumn, it would be expected that the number of larvae will also be down. At very dry sites such as Sherwood Heath SSSI, the effects of dehydration on larvae would perhaps be more evident than at Clipstone Old Quarter and the contrasting numbers of adults found at both sites since 2008, would certainly seem to indicate this.

But two other factors to consider are food availabilty (which should be as much affected by rainfall as larval growth) and temperature. Wet weather usually means milder temperatures, so we have generated the graph in Figure 01 to show the monthly minimum and maximum daytime temperatures over the same number of years. Again the data is from Waddington, Lincolnshire.

If the average larval size for the period April 1st - 7th 2009 is true, then the mean temperature over Winter could also have had some effect on the over-wintering success of larvae. This could mean that larvae were able to hunt and find food on mild Winter nights. However, the large number of larvae found at Clipstone Old Quarter in Spring 2011, would indicate that larvae are also quite capable of surviving several weeks of almost constant sub-zero temperatures, following the very cold November and December 2010.

 
1.6 ... Site map and survey sections

This image of the Clipstone Old Quarter survey route above, measures approximately 1,300 metres from north to south (A-D).The two yellow dots marked T1 and T2, indicate the on-site locations of ground temperature measurements, with T2 being the highest of the two points. The central grid reference for the site is SK 60549 67012.

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2.0 ... Summary and review of larval size range data from Spring 2009 - 2012

Although Project 2: Phase 1. 2012 officially began in August 2012, we felt it important that the opportunity was taken to collate and publish our larval size data from previous years.

Our most detailed recording of larval size ranges has always come during Spring (late February to early May) when larval activity resumes after Winter dormancy/hibernation and so the first part of this research looks at the size data from Spring 2009, 2010 and 2011, before examining the data collected in Spring 2012.

Surveying for larvae takes place during the early evening, once the afternoon and evening temperatures generally improves to above 10C and usually takes just over an hour to complete.

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Table 03. .. Glow Worm larval size ranges found during April 2009 - 2012
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    1cy Larvae size range (9mm-15mm)   Intermediate   2cy Larvae size range (19mm-28mm)
Apr 2009 Total % .. 0.00 0.00 0.00 0.00 0.00 0.00 1.81 .. 5.45 1.81 7.27 .. 1.81 7.27 5.45 16.36 20.00 10.90 10.90 9.09 1.81 0.00
Apr 2010 Total % . 0.00 0.00 0.00 0.00 1.14 1.14 14.94 .. 14.94 5.74 8.04 .. 9.19 10.34 4.59 3.44 4.59 8.04 10.34 2.29 1.14 1.14
Apr 2011 Total % . 0.00 0.00 0.00 0.00 1.61 0.53 8.60 . 9.67 10.21 11.29 . 9.13 17.74 6.98 6.98 4.83 2.68 5.37 0.53 1.61 0.00
Apr 2012 Total % . 0.00 0.00 0.00 0.00 2.56 2.56 10.25 . 2.56 12.82 10.25 . 15.38 5.12 10.25 7.69 5.12 7.69 2.56 0.00 7.69 0.00
 
Table 03a. .. Combined percentage of Glow Worm larval size ranges during April 2009 - 2012
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Apr 2009 Total % .. Larvae size range (9mm-15mm) 02.00% .. Intermediate 11.00% .. Larvae size range (19mm-28mm) 87.00%
Apr 2010 Total % . Larvae size range (9mm-15mm) 16.00% . Intermediate 29.00% . Larvae size range (19mm-28mm) 55.00%
Apr 2011 Total % . Larvae size range (9mm-15mm) 11.00% . Intermediate 31.00% . Larvae size range (19mm-28mm) 58.00%
Apr 2012 Total % . Larvae size range (9mm-15mm) 15.00% . Intermediate 23.00% . Larvae size range (19mm-28mm) 62.00%
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Tables 03 and 03a summarise the larval size range data and percentage of 1cy, 2cy and intermediate size range larvae recorded between April 2009 - 2012. April has been chosen as the standard month in the tables, as it consistantly produces the most larvae found in sections A, B, C and D of all the Spring months.
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Table 04. .. Average monthly 1cy and 2cy larval size ranges recorded during Spring 2009 - 2012
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    1cy larvae   2cy larvae
.. .. 2009 .. 2010 .. 2011 .. 2012 .. 2009 .. 2010 .. 2011 .. 2012
March .. .. .. .. .. 14.37mm .. .. .. .. .. .. .. 20.20mm .. .23.25mm
April .. 15.00mm .. 14.92mm .. 14.65mm .. 14.50mm .. 23.13mm .. 22.42mm .. 21.04mm .. 22.00mm
May .. 14.00mm .. 15.00mm .. .. .. .. .. 23.08mm .. 23.81mm .. 23.75mm .. 22.00mm
  It is quite obvious that most Spring larvae recorded from these sections are in their second calendar year and reaching the pre-pupation stage. But we have recorded larvae with prey on two occasions, so larvae do hunt on this stretch of path in the Spring.
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Table 04 reveals that the average length of 1cy larvae is 14.63mm found over four years. This gives us a good indication of larval growth before over-wintering for the first time and shows that most larvae will put on about 10mm growth after hatching from the egg. An average length of 22.46mm, shows that 2cy larvae double their size before over-wintering for a second time. Bear in mind that these are averages for the period April 1st - 7th and that we have recorded larvae with lengths of between 13mm and 28mm in our surveys.
     
     
2.1 ... Spring 2009 larval size data
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Table 05. .. The average larval size ranges recorded during Spring 2009
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  1cy 2008 larval size ranges   Intermediate   2cy 2007 larval size ranges
March N/A .. N/A .. N/A
April 15.00mm/1 .. 16.76mm/8 .. 22.42mm/46
May 14.00mm/1 .. 18.00mm/2 .. 23.81mm/35
  Based on Glow Worm larvae having a two year period of development, larvae found during Spring 2009, would originate from eggs laid by females in 2008 and 2007. A total of 94 larvae were recorded and measured during the Spring, with an early record of a 22mm larva found with prey under bark on 09/03/09. Larvae were recorded regularly from 05/04/09 onwards, but just two larvae fitting the 1cy size range were recorded.
     
Table 06. .. Glow Worm larval size ranges found during April 2009
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    1cy 2008 larval size ranges (9mm-15mm)   Intermediate   2cy 2007 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. .. .. .. .. .. .. 1 .. 2 .. .. .. .. 1 .. 1 1 2 2 1 1 ..
B .. .. .. .. .. .. .. .. .. .. .. 1 .. .. 1 2 .. 1 1 2 3 .. ..
C .. .. .. .. .. .. .. .. .. .. 1 2 .. .. .. .. 1 3 .. .. .. .. ..
D .. .. .. .. .. .. .. .. .. 1 .. 1 .. 1 2 1 7 6 3 2 1 .. ..
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    1cy 2009 larvae size range (9mm-15mm) 2.00%   Intermediate 16.00%   2cy 2008 larvae size range (19mm-28mm) 82.00%
Total %   0.00 0.00 0.00 0.00 0.00 0.00 1.81 .. 5.45 1.81 7.27 .. 1.81 7.27 5.45 16.36 20.00 10.90 10.90 9.09 1.81 0.00
 
 
Table 07. .. Glow Worm larval size ranges found during May 2009
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    1cy 2008 larval size ranges (9mm-15mm)   Intermediate   2cy 2007 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 2 .. 1 2 3 .. .. ..
B .. .. .. .. .. .. 1 .. .. .. .. .. .. .. .. .. 1 2 1 3 .. .. ..
C .. .. .. .. .. .. .. .. .. .. .. 1 .. .. .. .. .. 1 .. 3 1 .. ..
D .. .. .. .. .. .. .. .. .. .. .. 1 .. .. 7 1 1 3 1 1 1 .. ..
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    1cy 2009 larvae size range (9mm-15mm) 3.00%   Intermediate 5.00%   2cy 2008 larvae size range (19mm-28mm) 92.00%
Total %   0.00 0.00 0.00 0.00 0.00 2.63 0.00 .. 0.00 0.00 5.26 .. 0.00 18.42 7.89 5.26 18.42 10.52 26.31 5.26 0.00 0.00
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Figure 02. .. Larval size and activity profile in Spring 2009
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  Tables 06 and 07 show the larval growth rate during April and May 2009. Note the fewer intermediate larvae recorded during May and the recorded increase in 2cy larval size, which is evident through the higher percentage of 2cy larvae from the total number of larvae recorded.

Figure 02 shows the larval sizes grouped into four size categories of 12-16mm, 17-21mm, 22-24mm and 25-28mm.

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Apart from helping to illustrate larval growth throughout Spring 2009, the peak dates for larval activity are also shown to have occurred between April 22nd and May 14th. Two larvae were subsequently found on 19/05/09 and 22/05/09 and the first adult females to appear, were two on 27/05/09.
     
     
2.2 ... Spring 2010 larval size data
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Table 08. .. The average larval size ranges recorded during Spring 2010
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  1cy 2009 larval size ranges   Intermediate   2cy 2008 larval size ranges
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March N/A .. N/A .. N/A
April 14.80mm/15 .. 16.76mm/25 .. 22.42mm/48
May 15.00mm/1.. .. 17.33mm/3.. .. 23.81mm/11
  Based on Glow Worm larvae having a two year period of development, larvae found during Spring 2012, would originate from eggs laid by females in 2009 and 2008.

A total of 103 larvae were recorded from sections A, B, C and D. The first of the year were two on 04/04/10, found in sections L (not used in the data calculations) and in D. Larvae were then found regularly from 06/04/10, including notable counts of ten on both 23/04/10 and 25/04/10.

 
Table 09. .. Glow Worm larval size ranges found during April 2010
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    1cy 2009 larval size ranges (9mm-15mm)   Intermediate   2cy 2008 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. .. .. .. .. .. .. 1 .. 1 1 2 .. 1 2 .. 2 .. 3 1 1 .. ..
B .. .. .. .. .. .. .. 6 .. 4 .. 3 .. 4 2 1 .. 3 1 4 .. .. ..
C .. .. .. .. .. .. .. 1 .. .. 2 1 .. 1 2 2 1 1 1 2 .. 1 ..
D .. .. .. .. .. 1 1 5 .. 8 2 1 .. 2 3 1 .. .. 2 2 1 .. 1
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    1cy 2009 larvae size range (9mm-15mm) 16.00%   Intermediate 29.00%   2cy 2008 larvae size range (19mm-28mm) 55.00%
Total %   0.00 0.00 0.00 0.00 1.14 1.14 14.94 .. 14.94 5.74 8.04 .. 9.19 10.34 4.59 3.44 4.59 8.04 10.34 2.29 1.14 1.14
 
 
Table 10. .. Glow Worm larval size ranges found during May 2010
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    1cy 2009 larval size ranges (9mm-15mm)   Intermediate   2cy 2008 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. .. .. .. .. .. .. 1 .. .. .. .. .. .. .. .. .. .. .. 1 .. .. ..
B .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1 3 1 .. ..
C .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1 .. .. .. ..
D .. .. .. .. .. .. .. .. .. 1 .. 2 .. 1 .. .. 1 1 1 .. .. .. ..
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    1cy 2009 larvae size range (9mm-15mm) 7.00%   Intermediate 20.00%   2cy 2008 larvae size range (19mm-28mm) 73.00%
Total %   0.00 0.00 0.00 0.00 0.00 0.00 6.66 .. 6.66 0.00 13.33 .. 6.66 0.00 0.00 6.66 6.66 20.00 26.66 6.66 0.00 0.00
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Figure 03. .. Larval size and activity profile in Spring 2010
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  One difference between 2010 and 2009 was the higher numbers of 1cy and intermediate larvae recorded during April (see Table 08). But a comparison with the larval size and activity profiles in Figures 03 and 02, shows a very pronounced peak in the number of larvae recorded between April 22nd and 29th.

The first adult females appeared on 24/05/10, a few evenings earlier than in 2009.

     
     
2.3 ... Spring 2011 larval size data
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Table 11. .. The average larval size ranges recorded during Spring 2011
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  1cy 2010 larval size ranges   Intermediate   2cy 2009 larval size ranges
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March 14.37mm/8.. .. 17.00mm/5. .. 20.20mm/15..
April 14.65mm/20 .. 17.03mm/58 .. 21.04mm/104
May N/A .. 18.00mm/1.. .. 23.75mm/4....
  Based on Glow Worm larvae having a two year period of development, larvae found during Spring 2011, would originate from eggs laid by females in 2009 and 2010.

With the extremely cold period of weather in late November and throughout the whole of December 2010, it was always uncertain how successful larval over-wintering would be.

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But after the last of the remaining snow melted in early January, the remainder of the Winter became mild and dry. The favourable weather meant it was suitable for surveying to begin earlier than it had in 2009 and 2010.

A good amount of valuable larval size data was collected and an accurate picture of the increases in larval size between March and May is apparent in Tables 12, 13 and 14. Note the increase in intermediate size larvae during April in Table 13. 2011 proved to be exceptional for numbers of Spring larvae, eventually providing a total of 214 larvae.

     
Table 12. .. Glow Worm larval size ranges found during March 2011
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    1cy 2010 larval size ranges (9mm-15mm)   Intermediate   2cy 2009 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. .. .. .. .. .. .. 1 .. .. .. .. .. 1 1 .. .. .. .. .. .. .. ..
B .. .. .. .. .. 1 1 2 .. .. 1 .. .. 1 1 .. .. .. .. .. .. .. ..
C .. .. .. .. .. .. .. .. .. .. .. .. .. 2 .. .. .. .. .. 1 .. .. ..
D .. .. .. .. .. .. 2 1 .. 1 2 1 .. 3 2 2 .. 1 .. .. .. .. ..
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    1cy 2010 larvae size range (9mm-15mm) 29.00%   Intermediate 18.00%   2cy 2009 larvae size range (19mm-28mm) 53.00%
Total %   0.00 0.00 0.00 0.00 3.57 10.71 14.28 .. 3.57 10.71 3.57 .. 25.00 14.28 7.14 0.00 3.57 0.00 3.57 0.00 0.00 0.00
 
 
Table 13. .. Glow Worm larval size ranges found during April 2011
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    1cy 2010 larval size ranges (9mm-15mm)   Intermediate   2cy 2009 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. .. .. .. .. .. .. 1 .. .. 1 3 .. 2 8 .. 1 1 .. 2 .. 1 ..
B .. .. .. .. .. .. .. 5 .. 1 3 3 .. 5 8 3 4 5 3 3 1 1 ..
C .. .. .. .. .. .. .. 1 .. 1 1 2 .. 2 1 .. .. .. .. 1 .. 1 ..
D .. .. .. .. .. 3 1 9 .. 16 14 13 .. 8 16 10 8 3 2 4 .. .. ..
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    1cy 2010 larvae size range (9mm-15mm) 11.00%   Intermediate 31.00%   2cy 2009 larvae size range (19mm-28mm) 58.00%
Total %   0.00 0.00 0.00 0.00 1.61 0.53 8.60 .. 9.67 10.21 11.29 .. 9.13 17.74 6.98 6.98 4.83 2.68 5.37 0.53 1.61 0.00
 
 
Table 14. .. Glow Worm larval size ranges found during May 2011
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    1cy 2010 larval size ranges (9mm-15mm)   Intermediate   2cy 2009 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
B .0. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1 .. .. 1 .. .. .. ..
C .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
D .. .. .. .. .. .. .. .. .. .. .. 1 .. .. .. .. .. .1. .. .. .. 1 ..
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    1cy 2000 larvae size range (9mm-15mm) 0.00%   Intermediate 20.00%   2cy 2000 larvae size range (19mm-28mm) 80.00%
Total %   0.00 0.00 0.00 0.00 0.00 0.00 0.00 .. 0.00 0.00 20.00 .. 0.00 0.00 20.00 0.00 20.00 20.00 0.00 0.00 20.00 0.00
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Figure 04. .. Larval size and activity profile in Spring 2011
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  The larval season was over very suddenly in early May, with a single larvae recorded on 03/05/11 and then four on 05/05/11. The graph in Figure 04 illustrates well the very early season in 2011. Larval growth in late March and through April is clearly shown by the differing ratios of 12-16mm larvae to 17-21mm larvae.

Notable in 2011 is the high number of 17-21mm range larvae, compared to both previous years.

..
Apart from the much higher numbers, the ratio differences between the four larval sizes ranges in 2011 and both 2009 and 2010 are staggeringly contrasting. New record counts were reached on several dates, ultimately peaking at 22 larvae on 05/04/11. But double figure counts were also achieved on seven other dates. With continuing warm and dry weather, it was not surprising that female Glow Worms also appeared very early, with the first three appearing on 13/05/11.
     
     
2.4 ... Spring 2012 larval size data
..
Table 15. .. The average larval size ranges recorded during Spring 2012
..
  1cy 2011 larval size ranges   Intermediate   2cy 2010 larval size ranges
..
March N/A .. 17.00mm/3 .. 23.25mm/4.
April 14.50mm/6 .. 16.92mm/9 .. 22.00mm/24
May N/A .. 17.50mm/2 .. 22.00mm/20
  Based on Glow Worm larvae having a two year period of development, larvae found during Spring 2012, would originate from eggs laid by females in 2010 and 2011.

Very mild weather at the end of February produced two larvae on our first visit on 28/02/12. Hopes were then high, but several further surveys along sections A, B, C and D in early March, all proved negative.

..
Although a third larva was found on 11/03/12, it wasn't until 22/03/12 that regular surveying commenced, but the number of larvae recorded was low and gave cause for concern that the resulting adult glowing season would actually be poor. A count of 11 larvae on 30/04/12, raised hopes that our estimates would be wrong, but this remained our only double-figure larval count of the Spring.
     
Table 16. .. Glow Worm larval size ranges found during March 2012
..
    1cy 2011 larval size ranges (9mm-15mm)   Intermediate   2cy 2010 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
B .. .. .. .. .. .. .. .. .. .. .. 1 .. .. .. .. .. .. .. .. .. 1 ..
C .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
D .. .. .. .. .. .. .. .. .. 1 1 .. .. 1 1 .. .. .. .. .. .. 1 ..
..
    1cy 2011 larvae size range (9mm-15mm) 0.00%   Intermediate 43.00%   2cy 2010 larvae size range (19mm-28mm) 57.00%
Total %   0.00 0.00 0.00 0.00 0.00 0.00 0.00 .. 14.28 14.28 14.28 .. 14.28 14.28 0.00 0.00 0.00 0.00 0.00 0.00 28.57 0.00
 
 
Table 17. .. Glow Worm larval size ranges found during April 2012
..
    1cy 2011 larval size ranges (9mm-15mm)   Intermediate   2cy 2010 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. .. .. .. .. .. .. 1 .. .. 1 .. .. 1 .. .. .. 1 .. 1 .. 1 ..
B .. .. .. .. .. .. .. .. .. 1 1 ..1 .. .. .. 1 .. .1. 2 .. .. 2 ..
C .. .. .. .. .. 1 1 .. .. .. .. .. .. 1 .. 1 .. .. .. .. .. .. ..
D .. .. .. .. .. .. .. 3 .. .. 3 2 .. 4 .2 2 ..3 .. 1 .. .. .. ..
..
    1cy 2011 larvae size range (9mm-15mm) 15.00%   Intermediate 23.00%   2cy 2010 larvae size range (19mm-28mm) 62.00%
Total %   0.00 0.00 0.00 0.00 2.56 2.56 10.25 .. 2.56 12.82 10.25 .. 15.38 5.12 10.25 7.69 5.12 7.69 2.56 0.00 7.69 0.00
 
 
Table 18. .. Glow Worm larval size ranges found during May 2012
..
    1cy 2011 larval size ranges (9mm-15mm)   Intermediate   2cy 2010 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
A .. .. .. .. .. .. .. .. .. .. .. 1 .. .. .. .. .. .. .. .. .. 1 1
B .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1 1 1 1 2 .. .. .. ..
C .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 2 .. 1 .. 1 .. .. ..
D .. .. .. .. .. .. .. .. .. .. 1 .. .. .. 1 1 1 3 1 1 .. .. ..
..
    1cy 2011 larvae size range (9mm-15mm) 0.00%   Intermediate 9.00%   2cy 2010 larvae size range (19mm-28mm) 91.00%
Total %   0.00 0.00 0.00 0.00 0.00 0.00 0.00 .. 0.00 4.54 4.54 .. 0.00 9.09 18.18 9.09 18.18 13.63 9.09 0.00 4.54 4.54
 
..
Figure 05. .. Larval size and activity profile in Spring 2012
..
  Figure 05 shows the larval size and activity profile for Spring 2012.

There was a return to peak larvae numbers being more in line with that of 2009 and 2010 (the last week of April) and in many ways, the activity profile is quite similar to that produced in 2009, although the number of larvae is less.

Length measurements for 70 larvae were collected, which includes the two February larvae. Adult females appeared from 30/05/12.

 
     
3.0 ... Larval activity and bioluminescence during the late Summer and Autumn

Nationally and historically, little study seems to have been devoted to the activity of Glow Worm larvae after the end of the adult glowing season in early August. Certainly we had very little data ourselves, so even if just for our own reasons, we decided to make a concerted effort to expand our knowledge of larval activity during the Autumn.

Project 2: Phase 1. 2012, was designed to run in conjunction with Project 1: Phase 1. 2012, which is looking more into larval bioluminescence. Despite having gained a great deal of knowledge about the glowing habits of female Glow Worms, we had very little knowledge of the post-adult season. Some aspects we wanted to find more about were larval distribution in relation to forest paths and tracks, their typical hunting range and activity during the latter months of the year. These, coupled with certain aspects of larval bioluminescence and behaviour in the wild, compared to that exhibited by captive larvae, all go to form the basis for Project 1: Phase 1. 2012.

3.1 ... Autumn 2012 larval size data

Since 2009, we had made casual notes and records of any larvae found during surveys for adults at Clipstone Old Quarter and at the start of 2012, we only held size data for 30 larvae out of a total of 43 larvae found in the months June -August since 2009, so concerted research commenced in August 2012. This section details and breaks down the available data.

By the end of December 2012, we had accumulated larval size and age ratio data for 154 larvae out of a total of 180 found on 35 evenings/nights. This at least provides us with a baseline for further research. After several evening surveys, we had already gathered enough data to realise that most larvae fell quite clearly into two distinct groups. These groups were based on larval size ranges of 9-15mm (1cy) and 19-28mm (2cy). As we mentioned earlier, some larvae fall into a size range between the two main groups and are referred to as 'intermediate'.

..
Table 19. .. The average larval size ranges recorded during Autumn 2012
..
  1cy 2011 larval size ranges   Intermediate   2cy 2010 larval size ranges
..
July 12.40mm/5. .. N/A .. N/A
August 12.68mm/50 .. 16.89mm/19 .. 22.30mm/33
September 13.40mm/5. .. 17.22mm/9. .. 22.50mm/8..
October 14.11mm/9. .. 18.00mm/3. .. 21.41mm/17
..
Spring Avg 14.63mm/52 .. 16.69mm/115 .. 22.46mm/321
  So based on larvae having a more or less two year period of development, most larvae found during Autumn 2012, would still originate from eggs laid by females in 2010 (2cy) and 2011 (1cy).

Table 19 shows the average larval size ranges recorded each month during Autumn 2012.

The averages have been calculated where data is available for at least five larvae, so we were able to include larval size data for July, but have omitted two larvae recorded in November.

..
The average larval size ranges calculated from all Spring larvae, are also given in the table for comparison purposes. Interestingly, the sizes of both 1cy and 2cy size groups, show the expected increase in size from July to October and fall in line with average larval lengths that are found during the Spring.
     
Table 20. .. Glow Worm larval size ranges found during August 2012
..
    1cy 2011 larval size ranges (9mm-15mm)   Intermediate   2cy 2010 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
D .. .. .. 1 .. 1 .. 1 .. 1 .. .. .. .. .. .. .. .. .. .. .. .. ..
E .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1 .. .. .. .. ..
F .. .. .. .. 1 .. .. .. .. .. .. 1 .. 2 .. .. .. .. .. .. .. .. 1
G .. .. .. .. .. 1 .. 1 .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
I .. .. .. .. .. .. 1 .. .. .. .. .. .. .. .. .. 1 .. .. 2 .. .. ..
J .. .. 4 4 6 11 8 6 .. 7 5 5 .. 1 8 1 6 2 3 3 1 .. ..
K .. .. .. .. 1 .. 1 1 .. .. .. .. .. .. .. .. .. .. 1 .. .. .. ..
L .. 1 .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
M .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
..
    1cy 2011 larvae size range (9mm-15mm) 49.0%   Intermediate 18.0%   2cy 2010 larvae size range (19mm-28mm) 33.0%
Total %   0.98 3.92 4.90 7.84 12.74 9.80 8.82 .. 7.84 4.90 5.88 .. 2.94 7.84 0.98 6.86 2.94 3.92 4.90 0.98 0.00 0.98
 
 
Table 21. .. Glow Worm larval size ranges found during September 2012
..
    1cy 2011 larval size ranges (9mm-15mm)   Intermediate   2cy 2010 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
D .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1 .. .. .. .. .. ..
E .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
F .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
G .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
I .. .. .. .. .. .. .. 1 .. .. .. .. .. .. .. .. 1 .. .. .. .. .. ..
J .. 1 .. .. .. 1 .. 1 .. 2 3 2 .. 1 1 .. 1 .. .. .. .. 1 ..
K .. .. .. .. .. .. .. 1 .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
L .. .. .. .. .. .. .. .. .. .. .. 2 .. .. .. .. .1 .. .. 1 .. .. ..
M .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
..
    1cy 2011 larvae size range (9mm-15mm) 23.0%   Intermediate 41.0%   2cy 2010 larvae size range (19mm-28mm) 36.0%
Total %   4.54 0.00 0.00 0.00 4.54 0.00 13.63 .. 9.09 13.63 18.18 .. 4.54 4.54 0.00 18.18 0.00 0.00 4.54 0.00 4.54 0.00
 
 
Table 22. .. Glow Worm larval size ranges found during October 2012
..
    1cy 2011 larval size ranges (9mm-15mm)   Intermediate   2cy 2010 larval size ranges (19mm-28mm)
Section .. 9mm 10mm 11mm 12mm 13mm 14mm 15mm .. 16mm 17mm 18mm .. 19mm 20mm 21mm 22mm 23mm 24mm 25mm 26mm 27mm 28mm
D .. .. .. .. .. .. .. 1 .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
E .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
F .. .. .. .. .. .. .. .. .. .. .. .. .. 1 .. .. .. .. .. .. .. .. ..
G .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
I .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1
J .. .. .. .. .. 2 4 2 .. .. .. 3 .. 2 3 4 1 3 1 .. .. .. ..
K .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
L .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
M .. .. .. .. .. .. .. .. .. .. .. .. .. .. 1 .. .. .. .. .. .. .. ..
..
    1cy 2011 larvae size range (9mm-15mm) 31.0%   Intermediate 10.5%   2cy 2010 larvae size range (19mm-28mm) 58.5%
Total %   0.00 0.00 0.00 0.00 6.89 13.79 10.34 .. 0.00 0.00 10.34 .. 10.34 13.79 13.79 3.44 10.34 3.44 0.00 0.00 0.00 3.44
The above table does not include a 7mm long larvae recorded on 24/10/12, originating from a 2012 female.
 
 
3.2 ... On site larval distribution and hunting range
..
We regularly surveyed nine sections of the study site, but the most profitable was section J shown on the right. This section of forest track runs north to south on a gentle incline, protected from the worst of the elements by a belt of mature Pines which will be felled during the Winter 2012/2013. The sides of the track have become banked after years of track levelling, following the Dukeries Car Rally held in June each year. Bracken and Grasses dominate the vegetation, so section J is in many ways typically representative of several other sections found on site.

Just why this section proved to be so productive for larvae remains a mystery. Temperature may well be the key factor, as the upper reaches of section J marks the highest elevation point and so the recorded temperature here (T2 on the map in section 1.6) is usually recorded to be at least 1C higher than the lowest sections of the site (T1).

But even larval location and activity in section J, showed considerable differences and became split at the end of August, after which we recorded no further larvae from the lower half of this section for the rest of the year.

 
..
In October, larval location in the top half of section J eventually ended and the two late larvae recorded on 12/11/12 were an isolated occurrence, with single bioluminescent glows from both larvae thought to be due to the immediate presence of other invertebrates rather than hunting activity.

Larvae were found to hunt just off the forest tracks and paths, virtually always remaining within the vegetation boundary and individual larvae could be present in one small area for several consecutive evenings. Evidence suggested that hunting is largely confined to substrate under vegetation such as Bracken and Bramble, often within light grass and leaf litter etc along the Bracken line. Only two larvae were recorded from outside the vegetation limits.

..
3.3 ... Larval activity and bioluminescence

Table 23 shows our Autumn survey data for 37 site visits made between early August and late November 2012 and includes both day and night lengths, duration of site survey, the number of larvae found (tL) and the temperature (tC) at location T2.

One of our original research intentions had been to determine the peak time for larval activity, but although being able to confirm that during the late Summer and Autumn months, greatest activity occurred in August, we were unable to narrow down greatest larval activity to any particular time of night.

A decrease in the recorded numbers of larvae from September, was due to a general cessation of bioluminescent activity. This was found to coincide with a sudden drop in GPN (glows per night) rates and larval bioluminescence from captive larvae as part of Project 1: Phase 1. 2012.

If we look at the percentages of long duration glows recorded from wild larvae, the rate of larvae producing 20+ second bioluminesent glows suddenly rose from 5.3% (from a recorded total of 113 larvae) in August, to 15.38% (26 larvae) in September and then 16.12% (31 larvae) in October. So while larvae were clearly less inclined to glow, the proportion of long duration glows showed a marked increase from September onwards.

We believe that we are almost able to rule out lowering temperature as being the cause for this drop in GPN rates and possibly most larval activity, despite a run of successful evening surveys between 17/10/12 and 24/10/12, when the evening temperature again became very mild.

In captivity, two larvae were kept by ourselves in an unheated, naturally warm room at a constant temperature of 18 - 20C, with nine larvae under the supervision of Martin Dale also in an unheated room, but one subject to greater temperature fluctuations of 12 - 17C. Outdoor temperatures recorded from our Sherwood Forest study site, ranged from 6 - 17C during evening surveys between August and November. Despite the constantly warm temperatures larvae were kept at in captivity, the decline and eventual cessation of larval bioluminescence was in accordance with captive larvae kept at slightly lower temperatures by Martin Dale, and more importantly with larvae in the wild.

 
Table 23. .. Autumn 2012 survey data
..
Date Day length Night length Survey tL tC
..
04/08/12 15h:25m ..8h:35m 1h:30m 2 14C
16/08/12 14h:41m ..9h:19m 1h:00m 4 15C
17/08/12 14h:37m ..9h:23m 2h:50m 1 13C
19/08/12 14h:29m ..9h:31m 2h:00m 11 15C
20/08/12 14h:25m ..9h:35m 2h:00m 15 16C
21/08/12 14h:22m ..9h:38m 3h:35m 13 13C
22/08/12 14h:18m ..9h:42m 3h:50m 15 13C
23/08/12 14h:14m ..9h:46m 2h:25m 14 14C
24/08/12 14h:10m ..9h:50m 1h:40m 11 12C
25/08/12 14h:06m ..9h:54m 3h:45m 7 13C
26/08/12 14h:02m ..9h:58m 2h:05m 14 13C
27/08/12 13h:59m 10h:01m 2h:05m 3 14C
28/08/12 13h:54m 10h:06m 1h:45m 3 13C
15/09/12 13h:54m 11h:19m 3h:45m 18 11C
20/09/12 12h:41m 11h:40m 3h:10m 8 12C
22/09/12 12h:20m 11h:48m 1h:30m 1 ..8C
03/10/12 12h:12m 12h:34m 1h:00m 0 ..8C
10/10/12 11h:26m 13h:04m 2h:10m 3 ..9C
13/10/12 10h:56m 13h:15m 1h:05m 0 ..6C
15/10/12 10h:45m 13h:24m 1h:15m 0 ..8C
17/10/12 10h:36m 13h:32m 2h:00m 4 ..9C
18/10/12 10h:28m 13h:36m 2h:00m 2 11C
19/10/12 10h:24m 13h:40m 1h:50m 4 12C
20/10/12 10h:20m 13h:44m 2h:00m 1 ..8C
22/10/12 10h:16m 13h:52m 3h:15m 6 12C
23/10/12 10h:08m 13h:56m 3h:00m 11 12C
24/10/12 10h:04m 14h:00m 2h:30m 2 10C
25/10/12 10h:00m 14h:04m 1h:10m 0 ..7C
06/11/12 ..9h:56m 14h:52m 1h:30m 0 ..8C
07/11/12 ..9h:05m 14h:55m 1h:30m 0 ..8C
08/11/12 ..9h:01m 14h:59m 1h:00m 0 10C
09/11/12 ..8h:57m 15h:03m 1h:05m 0 ..8C
10/11/12 ..8h:54m 15h:06m 1h:00m 0 ..6C
12/11/12 ..8h:47m 15h:13m 1h:10m 2 ..8C
26/11/12 ..8h:21m 15h:39m 1h:00m 0 ..6C
16/12/12 ..7h:51m .16h:21m 0h:35m 0 ..4C
22/12/12 ..7h:50m .16h:10m 0h:40m 0 11C
..
The contributing factor to the cessation of larval bioluminescence is strongly believed to be the change in day/night lengths and this was found to coincide directly at the point where the lengths of day and night became of equal on September 25th 2012.

Project 1: Phase 1. 2012 was devoted to recording larval bioluminescence, especially detecting recurring patterns of activity and a substantial amount of data was gathered regarding bioluminescence exhibited by hunting/active larvae and clear patterns of peaks and troughs were found.

We discovered that larvae could be categorised by their level of GPN (glows per night) and GPM (glows per minute) rates, finding that larvae clearly fell into two groups (high and low) within each category and based on their recorded levels of bioluminescent activity. In effect, a distinct proportion of larvae were found to glow almost nine times more frequently than others, based on the average GPN rates of both groups. The most extreme activity profile was recorded by Martin Dale, when Larva 3 produced 379 glows within a two hour observation period on 02/09/12. Captive larvae were recorded to glow well over 100 times per two hour observation period on 13 occasions.

..
Figure 06. .. The bioluminescent activity profile produced by Larva 3 on 02/09/12, recorded by Martin Dale during Project 1: Phase 1. 2012
..
In the wild, it was soon noted that the bioluminescent glow duration produced by hunting larvae, was quite obviously longer than that produced by captive larvae, but that the GPM and GPN rates of wild larvae were considerably less than most captive larvae, although in line with those captive larvae showing a low GPM rate. Although the data gathered from the two wild larvae is limited, we believe that there is enough available data to use as a direct comparison with captive larvae, if we use the averages for two larvae we (TDP) kept in captivity.

A wild larva found on 15/09/12 was recorded glowing eight times within a ten minute observation period. Two bioluminescent glows lasted for 10 seconds, leading to an average glow duration of 7.33sec/6 if the 10+sec glows are taken out of the calculations. Add in the 10+sec duration glows and an average glow duration of 8.00sec/8 is reached. Based on this short observation, the larva had a maximum GPM rate of 2.00.

The bioluminescent data for the second wild larvae found on 19/10/12, gives averages of 7.88sec/4, if the 10+sec glows are taken out of the calculations and 12.46sec/13 with the inclusion of 10+sec duration glows. What was interesting about this larva, was the high number of long duration glows, producing nine long glows out of a total of 13 in a 15 minute observing period, including single glows of 20sec and 26 sec duration. This larva also produced a maximum GPM rate of 2.00.

3.4 ... Larval activity in relation to ground temperatures

Figure 07 shows the larval counts and survey dates against the temperature recorded at T2. Larval bioluminescence and activity clearly changed as the months progressed, as the nights lengthened and as the average temperature dropped.

..
Figure 07. .. Larval counts and on site temperature
..
  Female Glow Worms rarely glow if the temperature is below 8C and the evening is damp but fine, but they will continue to glow in a torrential storm if they are already glowing. Yet females can be strangely absent on nights that seem perfect, almost as if the whole colony has had the night off, before duly reappearing the following evening.

This near complete 'lights out' phenomenon has occurred here several times over the past four years study and there seems to be no obvious explanation for it. Adult or larval bioluminescence and the governing factors which influence it, must obviously be considerably more complicated than we often suppose.

..
Larval activity seems very much in accordance with that of adults. Although evening rain seemed to deter larval activity, at least until after a lengthy period of dryness, rain early in the day seemed less likely to affect larval activity after dark. As long as the temperature held above 8C, larval activity could be expected, but once the nights had lengthened, counts dropped off, no matter how mild it was.

We did have several cold overnight temperatures and slight grass frosts early in October and these seemed to end most larval bioluminescence or activity for a time. But a rise in temperature for field surveys in mid-October, did produce an increase in the number of larvae found. Many larvae recorded in October, were located by long duration bioluminescent glows from stationary larvae, rather than short glows typical of active larvae found in August. Surveys on a run of relatively mild evenings when the temperature was above 8C during the first half of November, proved negative until two were eventually located glowing within leaf litter on our sixth evening survey. The carpet of fallen leaves and dying/collapsing vegetation, made surveying extremely difficult.

3.5 ... 1cy and 2cy population levels

Table 24 shows the average larval size ranges from August to October. We have not included the figures for July and November, due to the small number of larvae recorded. A 7mm larvae from a 2012 female was found on 24/10/12, so by the end of the year there were larvae resulting from eggs laid by females in three seasons.

..
Table 24. .. Table showing the percentage of larval size ranges and incorporating larvae within the 2012 size range
..
..............   2012 larvae size range (3mm-7mm)   2011 larvae size range (9mm-15mm)   Intermediate   2010 larvae size range (19mm-28mm)   Total larvae
Aug total % .. 0.00% .. 49.0% .. 18.0% .. 33.0% .. 104
Sep total % .. 0.00% .. 23.0% .. 41.0% .. 36.0% .. 22
Oct total % .. 3.00% .. 30.0% .. 10.0% .. 57.0% .. 30
..
The table shows a decrease in the percentage of 2011 larvae after August. Whether this indicates that larger larvae within the 2011 size range, put on enough growth to take them into the intermediate size range is unknown, but there was a considerable percentage rise in the number of intermediate larvae during September.

Similarly, the percentage of intermediate larvae dropped after September and there was found to be a rise in the 2010 larval size range during October, which could also be attributable to larval growth. Larval moult could also be a possible cause.

The whole moulting process is prolonged, effectively stopping larval activity for a couple of weeks at least. If mass larval moult occurs and is the cause, then this would have taken place in September for 2011 size range larvae and August and then possibly October for intermediate larvae. This of course is just theoretical and clearly more work is required.

 
..
We are happy that the number of larvae found in September and October, did provide us with an adequate sample of the larval population and size ranges on site and we can only base the percentages on larvae found glowing during the surveys. It is interesting that peak larval bioluminescence occurs in August after the adult glowing season has ended, when such a peak would perhaps be expected to be more in line with the adult season?
..
Table 25. .. The average larval sizes recorded during 2012
..
  2011 larval size ranges   Total larvae     Intermediate   Total larvae     2010 larval size ranges   Total larvae
February 15.00mm .. 1 .. .. 16.00mm .. 1 .. .. .. .. 2
March N/A .. A .. .. 17.00mm .. 3 .. .. 23.25mm .. 4
April 14.50mm .. 6 .. .. 16.92mm .. 9 .. .. 22.00mm .. 24
May N/A .. A .. .. 17.50mm .. 2 .. .. 22.00mm .. 20
June 13.00mm .. 1 .. .. 17.00mm .. 1 .. .. .. .. ..
July 12.40mm .. 5 .. .. .. .. .. .. .. .. .. ..
August 12.68mm .. 50 .. .. 16.89mm .. 19 .. .. 22.30mm .. 33
September 13.40mm .. 5 .. .. 17.22mm .. 9 .. .. 22.50mm .. 8
October 14.11mm .. 9 .. .. 18.00mm .. 3 .. .. 21.41mm .. 17
November .. .. .. .. .. .. .. .. .. .. 23.00mm .. 1
December .. .. .. .. .. .. .. .. .. .. .. .. ..
..

The average larval sizes recorded during 2012 are shown in Table 25. Averages based on small numbers of larvae are unreliable and are included in the table for completeness only.

3.6 ... Mortality rates within the larval population

Our Project 2: Phase 1. 2012 research gave us some indication of larval mortality rates in the wild, suggesting that they were higher in the first year. Based on the small size of larvae within the first 12 months of life, a higher mortality rate would be expected. As the beginning of larval life coincides at a time when potential predators are also emerging from the egg, predator numbers will also be high.

..
It is generally believed that Glow Worm larvae have few, if any predators, as they are considered to be poisoness or at least taste unpleasant. But in order for a predator to discover and remember this, then they must surely have to attempt attack first? Between August and October 2012, we recorded a total of nine instances where wild larvae were found glowing within approximately 1.00cm of other invertebrates. Bioluminescence from the stationary larvae, suggested that both parties had just come into immediate contact and that larval bioluminescence was clearly a responsive and/or a defensive reaction to the encounter.  
Table 26. .. Theoretical success and mortality rates within Glow Worm larvae
..
  .. nF .. nL .. eF .. Ls .. Lm
2011 (1cy) .. 100 .. 64 .. 20 .. 3.20% .. 96.80%
2010 .. 100 .. 64 .. 50 .. 1.28% .. 98.72%
.. .. .. .. .. .. .. .. .. .. ..
2010 (2cy) .. 101 .. 58 .. 20 .. 2.87% .. 97.13%
2011 .. 101 .. 58 .. 50 .. 1.14% .. 98.86%
..
Among the selection of invertebrates were two predatory species. The very common Wolf Spider Pardosa amentata (Lycosidae) was recorded with larvae on two occasions and the small Ground Beetle Notiophilus biguttatus (Carabidae) once. Invertebrates offering no threat, but appearing to initiate a bioluminescent reaction, were the Common Rough Woodlouse Porcellio scaber (Porcellionidae), Common Shiny Woodlouse Oniscus asellus (Oniscidae) and the Pill Millipede Glomeris marginata (Glomeridae) which was recorded on four occasions with larvae.

But we believe larval mortality is as likely from human interference and dehydration, as it is through predation.

Our adult female and larval data for section J of the study site, can be used to provide theoretical mortality rates among the larval population. The number of female Glow Worms (nF) recorded in section J, was approximately 100 in 2011 and 101 in 2010. The number of larvae (nL) found during Autumn 2012 was 64 1cy larvae and 58 2cy larvae. In Table 26 above, these figures are shown, along with the theoretical number of eggs laid by females (eF), the larval success rate (Ls) and the larval mortality rate (Lm) calculated from the available or assumed data.

 
4.0 ... Proposed research work for Project 2: Phase 2. 2013

Phase 2 of our research sees the continuation of work we started as part of Phase 1. Whilst being able to make confident claims regarding some aspects of larval activity and bioluminescence, further data will enable us to confirm our claims. Very little is known of larval activity during the early months of the year, so our survey work will now continue throughout the year, rather than from March to August as it has since 2009. There still remains a great deal of work to be done and the following aspects of research are already planned for 2013.

  • To monitor for larval bioluminescent activity after over-wintering. We know that larvae become active from late February if the weather is mild, but we want to find out if larval bioluminescence occurs at the same time.
  • To then continue to monitor larval bioluminescent activity and gather data throughout Spring, Summer and Autumn 2013.
  • To continue to gather data on larval size ranges throughout the year.
  • To collect a number of wild larvae seperated by their high or low GPN and GPM rates and rear to adult in captivity, enabling accurate comparison with data collected from captive larvae in 2012.
  • To gather accurate data regarding air and ground temperature, substrate moisture, humidity and light levels throughout the year. Building up such data may help to determine any particular climatic conditions, conducive to both adult and larval bioluminescence.
  • To determine the height at which male Glow Worms fly using artificial lures on posts of different heights. This work will probably run in conjunction with Project 1: Phase 2. 2013.
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Please quote the following when referencing this document

Pendleton, T.A.. Pendleton, D.T. and Dale, M. "The size variation and age ratios found within the larval population of the Glow Worm (Lampyris noctiluca) during Autumn" www.eakringbirds.com; December 2012.

     
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