The research is based around data obtained from larvae at Clipstone Old Quarter, an area of commercial forestry within the confines of Sherwood Forest, Nottinghamshire.

This latest work sees some changes to theories and proposals published last year and in some instances, we are happy that we now have enough evidence or data, to conclude some aspects of our research.

Some text remains the same, but much has been re-written to incorporate the data and findings from our continued work over the course of 2013.

Project 2: Phase 2. 2013 was conducted by Trevor and Dilys Pendleton (TDP), based at Market Warsop, Nottinghamshire. We were once again aided 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".

The focus for our Project 2: Phase 1. 2012 research, was to continue the same work commenced back in 2012, by once again collating as much larval size range data from our study colony at Clipstone Old Quarter in Sherwood Forest, during the late Summer and Autumn of 2013.

The aims of this research are 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 8°C 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.

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.

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.

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.

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.

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.

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. Perhaps the real difficulty is created by the fact that some larvae could certainly reach adulthood within 12-14 months, if conditions were right and food was caught regularly. Other larvae could possibly take as long as three years before reaching the pupation stage. Growth is of course dependent on the larva's ability to find food.

We based our Project 2: Phase 1. 2012 data on the assumption that most Glow Worm larvae have a more or less 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, larvae hatched in 2010 would be in their second calendar year (2cy) while 2011 larvae would be in their first calendar year (1cy).

In Project 2: Phase 1. 2012, we proposed three possible examples of larval life cycles, based over different lengths of larval development.

1.5 ... Intermediate age range larvae

In Project 2: Phase 1. 2012, we clearly placed too much emphasis on relating larval size to age and it is unlikely that we will be continuing much further with this line of research.

Surveying in Spring 2013 provided us with some valuable data, enabling us to more or less prove that (aside from some individual exceptions) the majority of larvae falling within the 16-18mm 'intermediate' age range in April and May, and previously expected to remain as larvae till the following Spring, would go on to produce adult males the same year. We randomly collected six larvae measuring between 15mm and 18mm in length and kept them in captivity, but at outdoor temperatures. They were expected to remain as larvae for a further year, but all quickly pupated and produced males.

In the larval size charts, we originally categorised larvae into three groups or age ranges. These were 1cy (9mm-15mm), intermediate (16mm-18mm) and 2cy (19mm-28mm). We proposed that intermediate larvae were those whose length placed them in a grey area between both calendar year groupings, and that they could be either well developed 1cy larvae or poorly developed 2cy larvae. Alternatively, we believed that they could be 2cy larvae, with a third year of growth to complete before pupation.

Although it is possible that intermediate larvae make up a proportion of late emerging females in the second half of July, it now seems likely that (in Spring or late Autumn at least) that most intermediate larvae develop into adult males. It seems that the majority of larvae recorded nocturnally in the Autumn, have little growth to complete before pupation the following Spring. Therefore, in all the following larval size charts, we are categorizing larvae purely by size, rather than categorize them to a specific calendar year.

In Table 02 we have once again 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 site map) and compared them with the recorded rainfall between the months of April to August & September to March. Larvae found during late afternoon and early evening surveys, are now believed to be larvae in the pre-pupation stage, possibly feeding once more before pupation takes place.

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.

Reductions in the number of larva recorded during periods of very dry weather continues to be noted, whether during diurnal surveys in Spring, or nocturnal surveys during the Summer and Autumn. The effects of dehydration on the larval populations at very dry sites such as nearby Sherwood Heath SSSI, has been more evident than it has at Clipstone Old Quarter, and the contrasting numbers of adults found at both sites since 2008 (even with a reduction in adults at Clipstone Old Quarter) certainly seem to indicate this.

Harvesting Pines at Clipstone Old Quarter during the Winter of 2013-2014, is therefore likely to have a significant impact on the study site's future Glow Worm population. By opening up the site to increase the amount of lowland heath, will undoubtedly leave it prone to becoming much drier.

Quite remarkably and despite some evidence to suggest larval size might be linked to the amount of rainfall recorded (hence greater food availability) during the previous year, the average larval length between April 8-14th 2013, was lower despite a very wet 2012.

The decrease in average larval length has been dramatic, with larvae found to be over 5mm shorter in Spring 2013 than in Spring 2009. Dehydration means larvae become lethargic and unable to hunt successfully. Slugs and Snails are likewise affected by periods of adversely dry weather.

The very dry weather continued until September 6th, when a new site record count of 48 larvae came after the first day's rain for several weeks. There were signs that some larvae had finally either taken on water or had fed.

In Project 2: Phase 1. 2012 last year, we proposed that larvae may hunt on mild nights, even during Winter. However, our work in conjunction with Martin Dale, suggests that larvae remain largely inactive, even if replicating temperatures similar to those of Spring, Summer and Autumn. Martin did try increasing the amount of light to young larvae kept in captivity and this did prove to be more successful.

Due to us now believing that Glow Worm larvae cannot be categorised in to age groups purely by size accurately enough, the following larval size charts are now slightly different to those of last year.

We also believe that, as this is ongoing scientific research, anyone not having seen or read the data from Project 2: Phase 1. 2012, will still have all the information needed without having to read our initial findings.

Sections 2.1 - 2.6 deal purely in larval size data obtained during our diurnal surveys.

Noctural survey data is produced later.

Larvae were recorded regularly from 05/04/09 onwards, but just two larvae in the lower size ranges were recorded.

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

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.

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

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.

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

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.

There was a return to peak larval 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.

A total of 103 larvae were found during our late afternoon or early evening surveys, which was considerably more than in 2012, Yet the final total of females in 2013 was 100 lower than in 2012.

The average larval size of the Clipstone Old Quarter population, has decreased annually since 2009. This is probably due to periods of dry weather the previous late Summer and Autumn, ultimately causing larval dehydration, the inability to find food and then death.

3.0 ... Spring and Summer 2013 nocturnal surveying reports

Diurnal surveying of Glow Worm larvae has been ongoing at Clipstone Old Quarter for several years, but we had never surveyed nocturnally for larvae in Spring before. We had always recorded any larvae found, or larval bioluminescence produced during our surveys for adults, but had found that no (or at least very little) larval bioluminescence was very much in evidence before mid-July.

So a series of evening site visits began as early as the first week of January, to look for larval bioluminescence. Visits took place when the temperature was thought mild enough for larval activity. We determined in Project 2: Phase 1. 2012, that larval activity was best expected when the temperature was around 8ºC or above.

Six noctural surveys during January produced nothing and no surveys were conducted in February or March, as the temperature consistantly remained below 8ºC.

All was going well, until a prolonged cold February and March effectively stopped any chance of us recording larval bioluminescence around the time of the Spring Equinox.

Eight surveys in the second half of April again produced nothing, even though larvae were known to have become active from April 11th. 23 surveys were carried out during May and after more blank nights, larval bioluminescence was unexpectedly noted on May 10th, and then on an additional three more evenings ending on May 21st. Bioluminescence exhibited by all but three of the 24 larvae recorded during May, came from fully fed, pre-pupating larvae. A summary of the recorded bioluminescence is given below.

10/05/13. Six larvae found, all found between 23:10h and 00:00h. All glows single, from darkest areas of section J and of long duration (10+sec) One pupating male larva found glowing, eventually pupated on 16/05/13. Lowest T2 temperature recorded at 10°C.

12/05/13. Seven larvae found. Two larvae found within minutes between 22:50h and 23:00h, then five found between 23:50h and 00:30h. All glows single, from darkest areas of section J and of long duration (10+sec). Lowest T2 temperature recorded at 10°C.

15/05/13. Four larvae found. All producing single, long duration glows between 23:00h and 00:55h, with a temperature ranging from 5°C - 4°C at T2.

21/05/13. Seven larvae found. Some producing single, long duration glows, but three larvae produced several shorter glows before being measured. All larvae were found between 22:48h and 00:03h. Temperature of 11°C at T2.

One larva found glowing on the edge of a forest track on May 10th, was clearly in the early stages of pupation, even though it was in a completely open situation, covered only by a blade of grass. It eventually pupated on May 16th, before emerging on May 27th. On May 30th, a bright glow was found to be eminating from a freshly formed (still cream coloured) female pupa, tucked down the side of a loose stone. The location of this pupa was marked, the pupa left on site and monitored every other evening, but was found largely eaten, two or three days before expected emergence. It was believed to have been predated by other invertebrates.