Size variation and ratios of wild Glow Worm larvae during Autumn 2012
 
After the 2012 Glow Worm season had finished, surveying for larvae on several August evenings soon revealed that the majority of larvae fell into two obvious size ranges. Those measuring 9-15mm in length were presumed to be the result of eggs produced by females in 2011 and those of 19-26mm produced by females back in 2010.

Obviously there has to be an allowance for some variation in larval sizes between both years, depending on any larva's ability to find food. A number of larvae measured, fell into what we have termed an 'intermediate' age range of 16-18mm, as these larvae are difficult to assign to either specific age range, but could easily be from eggs produced by females in either 2010 or 2011. However, as our research continued from Autumn 2012 through to Spring 2013, we began to reconsider things.

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Glow Worm larval size ranges found during August 2012
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    2011 larval size ranges   Intermediate   2010 larval size ranges
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 .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
N .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
O .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
S .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
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    2011 larvae size range (9mm-15mm) 49.0%   Intermediate 18.0%   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
The table above shows the recorded larvae size ranges that we have size data for (104) out of a total of 113 larvae, found during the course of August 2012. The lower section of the table gives the percentages (either grouped by year or singularly by length) of larvae recorded within that size range.
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Glow Worm larval size ranges found during September 2012
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    2011 larval size ranges   Intermediate   2010 larval size ranges
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 .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
N .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
O .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
S .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
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    2011 larvae size range (9mm-15mm) 23.0%   Intermediate 41.0%   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
The table above shows the recorded larvae size ranges that we have size data for (22) out of a total of 26 larvae, found during the course of September 2012. The lower section of the table gives the percentages (either grouped by year or singularly by length) of larvae recorded within that size range.
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Glow Worm larval size ranges found during October 2012
..
    2011 larval size ranges   Intermediate   2010 larval size ranges
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 .. .. .. .. .. .. .. ..
N .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
O .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
S .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
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    2011 larvae size range (9mm-15mm) 31.0%   Intermediate 10.5%   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 13.89 13.89 3.44 10.34 3.44 0.00 0.00 0.00 3.44
The table above shows the recorded larvae size ranges that we have size data for (29) out of a total of 31 larvae, found during the course of October 2012. The lower section of the table gives the percentages (either grouped by year or singularly by length) of larvae recorded within that size range. Note: The above table does not include a 7mm long larvae recorded on 24/10/12, which would clearly originate from a 2012 female.
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Glow Worm larval count rates and evening temperature
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  The graph on the left shows the total number of larvae we have recorded on our site visits between August 16th and October 25th 2012 and the temperature taken at the same time.

Even with a limited dataset, the graph clearly shows that the number of larvae found, is fairly dependant on evenings when temperatures are at least 8C.

Mild conditions seems to become more important to any larval counts made during late October, when larval hunting activity shows an increase if mild evening/night temperatures persist over several dates.

     
Locations of Glow Worm larvae recorded nocturnally at Clipstone Old Quarter during 2012
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Autumn 2012 to Spring 2013 larvae survey results (nocturnal)
Date   Count     Additional notes
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August 16th   4     A short search for larvae this evening, produced three at the top of section J and one in section F. Larval sizes were 12mm, 14mm and two at 15mm. Weather, overcast and very mild, site visited from 23:15h-23:45h.
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August 17th   1     Another search for larvae this evening, resulted in one 10mm larva glowing on a small stone at the top of section J agian. Weather overcast with some light rain and site visited from 21:45h-22:45h.
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August 19th   11     11 larvae found this evening. Weather clear and mild. Site visited from 21:40h-23:30h.
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August 20th   15     15 larvae found this evening. Weather, partially clear skies and warm. Site visited from 21:30h-23:30h. Temperatures were 17C at T1 and dropping to just 16C atT2.
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August 21st   13     A total of 13 larvae were found this evening, which despite surveying several other sections, were all in section J. Weather, clear skies after torrential showers during the mid-late afternoon period, leading to temperatures of 13C at both T1 and T2.
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August 22nd   17     Nearly four hours surveying resulted in 17 larvae being found this evening/night. Larval sizes ranged from 9mm (our smallest ever) to 25mm. Sections D, E (lower part) F, G, I, J, K, L, M, N and S, were surveyed at least twice. Weather clear and mild with temperatures of 14C at T1 and 13C at T2 at 22:00h, dropping to 9C at T1 by 01:20h. Site visited from 21:40h-01:30h.
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August 23rd   14     14 larvae found this evening, with a 28mm female larva found in section F being the largest of the size ranges. The following sections were surveyed, D, E, F, G, I, J, K, L, M and O. Weather overcast and warm with no wind. Site visited from 21:20h-23:45h. Minimum temperatures of 13C at T1 and 14C at T2.
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August 24th   11     A total of 11 larvae were found this evening, Weather, overcast and cloudy, becoming wet with heavy rain. Site visited from 21:20h-23:00h.
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August 25th   7     Just seven larvae found this evening, with some evidence that they were becoming more active, the longer it stayed dry. Weather, heavy showers most of the day and well into the evening, with a temperature of 13C at T1 and T2. Site visited from 22:00h-01:45h.
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August 26th   14     14 larvae found this evening. Weather clear with a bright moon and temperatures of 12C at T1 and 13C at T2. Site visited from 21:10h-23:15h.
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August 27th   3     Just three larvae found this evening. Weather, rain most of the evening which cleared shortly before surveying, but feeling warm with a temperature of 14C at T2. Site vistied from 21:20h-23:25h.
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August 28th   3     A further three larvae found again, all were found in areas shaded from the bright moonlight which severely interfered with surveying. Weather, clear and mild with temperatures of 11C at T1 and 13C at T2. Site visted from 21:20h-23:05h.
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September 15th   18     A total of 18 larvae found this evening, with 16 of the total being found after 22:15h, when larvae seemed to become more active. The following sections were surveyed, D, F, G, I, J, K, L and M. Weather clear and mild with temperatures of 10C at T1 and 11C at T2 by 00:00h. Site visted from 20:45h-00:30h.
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September 20th   8     Eight larvae found this evening, with three located in section L. Sections L, M, N, K, J, D, S, F, G, I and E were all surveyed. Temperatures of 11C at T1 and 12C at T2 were recorded at 23:00h, weather overast and mild. Site visited from 21:00h-00:10h.
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September 22nd   1     Just a single larva (unmeasured) found glowing in section J this evening, probably due to the cooler temperature. Sections L, M, F, G, I, J and K were surveyed. Weather clear and cool, with temperatures of 7C at T1 and 8C at T2 at 21:00h. Site visited from 20:15h-21:45h.
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October 3rd   0     No larvae found this evening in an hour's surveying, but temperature only at 7C at T1 and 8C at T2. Sections L, K and J surveyed, with site visited from 19:30h-20:30h.
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October 10th   3     An hour's survey produced three hunting larvae near the top of section J this evening. Weather lightly overcast, with tempertures of 8C at T1 and 9C at T2. Sections F, K, J and L were surveyed.
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October 13th   0     No larvae found this evening, but a clear sky and tempertures of 6C at both T1 and T2. Sections L, M, J and K were surveyed. Site visited from 20:00-21:05h.
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October 15th   0     No larvae found. Weather clear and feeling mild, with tempertures of 8C at both T1 and T2. Site visted from 19:30h-20:45h.
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October 17th   4     Four larvae found this evening and all between 21:25h-21:55h. Weather lightly overcast, becoming cloudy with light rain and tempertures of 8C at T1 and 9C at T2, later dropping to 8C at T2. Sections D, F, I, J, K and L were surveyed.
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October 18th   2     Two larvae found. Weather, lightly overcast and mild with a temperature of 11C recorded at T1 and T2. Sections F, J, K, L, M and O were surveyed several times each. Site visited from 21:30h-23:30h.
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October 19th   4     Four larvae found in just under three hours surveying this evening. Weather overcast with some light rain, mild with initial tempertures of 12C at T2, later falling to 9C. Sections D, F, G, I, J, K and L were surveyed several times each. Site visited from 21:00h-23:50h.
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October 20th   1     Just a single larvae found this evening. Weather overcast with a temperature of 8C at both sites. Sections D, F, G, I, J, K, L, M and N surveyed. Site visited from 21:30h-23L30h.
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October 22nd   6     A surprising total of six larvae recorded this evening. Weather foggy (making the whole site extremely dark) and very mild, with a temperture of 12C, dropping to 11C at T2. Sections F, G, I, K, L and J were surveyed several times, but all larvae were found in the upper part of section J.
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October 23rd   11     The mild conditions seem to have prompted more larvae to become active, with a total of 11 found this evening. Weather overcast, with the cloud lowering after 22:00h. Temperature 12C at both T1 and T2. Sections D, F, G, I, J, K, L and M were surveyed. Site visited from 19:30h-22:30h.
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October 24th   2     Another mild and damp evening, but just two larvae found, although one of these measuring just 7mm in length was obviously off a 2012 female. Weather, overcast with almost constant drizzle with the temperature at T2 dropping from 12C to 10C. Sections D, F, G, I, K, J, L and M were surveyed. Site visited from 19:30-22:00h.
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October 25th   0     No larvae found this evening. Weather, lightly overcast, becoming clear with bright moonlight. Temperature of 7C at T2. Only the darker sections of F, G and J were surveyed because of moonlight interference. Site visited from 19:30h-20:40h.
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November 6th   0     No larvae found despite quite favourable temperatures of 8C at T2. Sections D, F, G, I and J were surveyed. Site visited from 19:30-21:00h.
 
November 7th   0     No larvae found. Weather lightly overcast with skies clearing. Temperature at T2 dropping quickly from 8C-6C. Sections D, J and F were surveyed. Site visited from 19:15h-20:45h.
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November 8th   0     No larvae found. Weather lightly overcast with the temperature at T2 dropping from 10C to 7C. Sections D and J were surveyed. Site visited from 20:10h-21:10h.
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November 9th   0     No larvae found this evening. Weather overcast with light rain and a temperature at T2 of 8C. Sections O, L, J and K were surveyed. Site visited from 20:15h-21:20h.
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November 12th   2     Two very late larvae found this evening in section J. Weather, clearing skies with temperature at T2 of 8C, dropping to 6C. Only section J was surveyed, site visited from 19:30h-20:30h.
 
November 13th   0     No larvae found this evening. Weather overcast and mild, with a temperature of 9C at both T1 and T2. Sections F, G, I, J, L and M were surveyed. Site visited from 18:05h-19:15h.
               
     
     
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