Glow Worms are still in national decline, disappearing from many of their former haunts through a series of influencing factors and is probably as deserving as having nationally notable B status as some that already do. It's importance as part of our native fauna then, is perhaps not in its rarity value, but as a public relations excercise, helping to create a greater awareness of our native fauna in both young and old.

Early Spring larval survey results and data

Once again, only sections A, B, C and D of the area were surveyed for larvae, by early May revealing a total of 231 larvae. The surveys produced a very surprising set of results, with early numbers well up on both previous years larval surveys. We had actually expected a poor year generally for numbers, based on the assumed two year larval stage and after having increased numbers of adults in 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, but after the last of the remaining snow melted in early January, the remainder of the Winter became relatively mild and dry.

Several visits were also made to check for larvae during the morning, while the path was still largely in shade. This was successful on each visit, usually providing better counts than those that had been achieved the evening before. This could have been down to the slight increase in moisture levels from any overnight dew, but may also have been down to the slightly lower temperature in the morning than in the late evening.

Larvae found on the path during the evening, were not all at the pre-pupation stage, although we believe that those found during the morning probably were (judging by their generally larger size). Several instances of active hunting were again observed along the surveyed path over the course of the Spring, illustrated in the left hand photograph.

The very early flight periods of many invertebrates locally, made it worth surveying for the first females much earlier in 2011 than we did in 2010. Starting our first survey on May 7th, the first three females all appeared nearly a week later on May 13th, about 14 days earlier than the previous year. This 14 day early period, remained pretty much applicable to much of the female data throughout the course of the glowing season, but there was nothing similar in terms of adult totals.

An addition to the colony surveying in 2011, was the recording of the ground temperature from two seperate locations. The two locations were chosen on paths at the lowest and highest points of the site. On most evenings when the sky was clear and there was little or no wind, both locations gave quite contrasting temperatures.

Further work on the number of glowing females and corresponding temperatures, may well be undertaken in 2012, by taking additional temperatures from the highest and lowest points in the grass strip. A trial evening doing this provided ground temperatures of 12°C and 11°C from the two path locations, with a grass temperature of 8°C.

An arial map showing the survey areas on site is produced below. The usual survey route taken was area O, R, L, M, N, P, K, J, F, G, H, I, D, E, C, B and finishing in A, but on a few occasions this year, we reversed the route order. 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 is SK 60549 67012.

This emergence came after the two previous nights yielded counts of just three and four respectively. Both these evenings were cool with temperatures of 7°C (T1) and 8°C (T2). It is of course entirely possible that the 50 new females had hatched out over the course of June 10th, 11th and 12th and glowed for the first time when the temperature rose on June 12th but this is rather hypothetical and there is no evidence of this happening.

This average peak is well shown in the following four graphs on the left of this text, showing the maximum weekly female counts from 2008 - 2011. The lack of daily coverage in 2008, probably renders that graph obsolete and is included here, only because it does illustrate the average seasonal peak.

Apart from the sheer numbers of females, 2011 was exceptional in the length of the season, lasting for 14 weeks.

August 21st finally marked the end of the season, although we did continue to make site surveys checking for other late emergences for a few days after that, but primarily the very early start to the season on May 13th, was certainly weather related. It is known that many other Glow Worm sites across the UK, are rarely checked much before June and even some sites in the very south of the UK, don't actually become 'active' until about that time. At least that is what is presumed or is evident through records sent to the UK Glow Worm Survey run by Robin Scagell.

The reason for this has always been climatic rather than anything else, with temperatures across the southern UK, always being a degree or so warmer than those in Nottinghamshire.

We personally think that our early Glow Worm records are just down to consistant early coverage and that the glowing season is just as early at many sites south of Nottinghamshire.

It's quite difficult to discern any real single peak in Table 01 for 2011. If the percentages in Table 01 and Table 01a are compared, note how it is May 25-June 1st 2011 and June 17-18th 2010 before 80% is reached. This shows that males appeared much earlier in 2011 than they did in 2010, but in similar fashion to 2009. There was then a drop in the number of males found with females, before a sudden rise and peak in numbers on June 12th and 13th. On these dates, we recorded 92% of females being mated on the first night. June 12th also coincided with the emergence of 50 females out of a count of 88 females, but numbers of males remained surprisingly low for a further few days.

Tables 02 and 02a show the figures for females glowing for two consecutive evenings/nights. There is a big jump from 2% - 22% of females glowing for two consecutive evenings only from Jun 12th, before the figures drop back down again. Where in 2010 the percentage of females glowing for two dates gradually lowered from 30% at the start of the season, then rose again near the end, the percentages in Table 02, again show a very mixed set of results. The only factor that could possibly account for this, was that there must have been several good emergences of males between mid-May and the end of June 2011.

Artificial lures have been used with effect at other UK sites, and are an easy way of determining the presence of Glow Worms by attracting males. They use a small battery powered LED light that can be placed on the ground, or preferably in light grass and their efficiency as an attractant is excellent.

The number of males present on site on June 3rd, was highlighted by an hour long experiment using two artificial lures in close proximity (of two types and at different heights) to attract males. One lure placed directly on the ground in light grass, had attracted a total of 17 males by 23:45h, but the other attracted none. Bearing in mind that just six females were present during our survey of June 3rd, it shows how the number of males present on site, is considerably underestimated.

The visible brief glow males produce, is something else we have noticed. It is always very difficult to detect and usually has to be corroborated by at least two observers to be recorded as genuine. These brief flashes are usually close to the ground at about grass height, but males do produce a more persistant very faint glow, if viewed in darkness from underneath.

We only used lures to attract males on isolated occasions, so that survey results were not affected. Among the benefits of using lures in the future, is that they could provide information on the height at which males fly, or how large an area they cover outside the colony boundaries.

100 males were recorded with females this year, with the first male appearing on May 17th after the first females on May 13th. This was very early, but probably not that unusual. Although our work has confirmed that males have a much shorter season than females, it's not unknown for males to appear more or less at the same time as the earliest females.

The next three graphs below show the numbers of females and the total number of males found in cop with females between 2009 and 2011.

Male records were rather erratic overall in 2011, but do seem to show several peaks of activity. Just one male was recorded with a female after the first week of July this year, similar to the record for the corresponding month in 2009. Females found with two males were F091 F106 F331 F527 F566 and F641, whilst three males were recorded with F348 and F567. The number of males in 2010 was actually greater, when there was a prolonged peak from the middle of June and into early July. In 2009, the activity level and numbers involved was much lower, but the length of the male season is virtually the same as in 2010.

On several occasions this year, we returned and conducted second surveys that lasted well into the early morning hours. These were to help determine how long females glow for. Though the number of return visits was not enough to gather any useful data, we did find that quite often, females unmated for any length of time (more than a week) would continue to glow till around 01:00h and occasionally 02:30h, though this was dependent on weather conditions and date. Females that had glowed for the first time during the initial survey that evening, were all found to have stopped glowing completely by the time we returned on site.

Where it was practical to do so, we also got into the habit of re-checking some survey sections an hour later, to see if females which were not glowing the first time, had started glowing by the time we checked again. This worked on many occasions, especially during the latter part of the season, but we still found it puzzling as to why females seemingly failed to glow when conditions seemed ideal. Checking the same female twice sometimes worked the other way - glowing when first checked, but not later. Sometimes females went 'missing' not glowing for three or four nights, then would reappear again. But we did have at least two instances where females failed to glow (or be found) for five nights, before appearing again in their usual location. Female 792 would later give us more of an insight into their glowing tendencies when she was taken into captivity.

Tables 04 and 04a show the average glowing periods of all females recorded during 2011 (792f) and 2010 (502f). The data from groups of 50 females is used and their inclusive dates are given. The average number of dates females glowed for in 2011 varied, although the pattern of a higher average, becoming shorter in peak season, then increasing again is clear.

Further notes and summaries of Glow Worm activity in survey sections A - R

Below is the arial map showing the female locations plotted as red dots and survey sections as white directional arrows during 2011. The yellow directional arrows show the movement of Glow Worms into areas of the site where adults had not been recorded previously. The central grid reference is SK 60549 67012.

Section N (photographed on the right) is a minor forest path, south-facing and although open to any weather approaching from the west and shaded for part of the morning, is still probably one of the warmest sections on site.

Vegetation either side of the path is short grass with some Bracken. Formerly bordered on both sides by Pine plantations, one side was clear-felled years ago and is now being restored to heathland. Glow Worms first appeared in this section in 2009, when small numbers were concentrated at the southern end of section N, despite the whole length of section N being walked over many times. 2010 saw records increase in both number and distance away from the original source, but the number of records in 2011, saw the whole of this section producing females for the first time.

The following tables show (and allow direct comparison) the numbers of new females recorded each week in sections A - R during 2011 and 2010. Each section is accompanied by a short summary.

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The late emergence of F792 in section G on August 5th was surprising, as it occurred two weeks after F791 appeared on July 22nd. Although we had presumed that there must be late adults, none had ever been recorded in previous years despite occasional checks on site.

Despite seeing nearly 2 000 females glowing, the actual lighting up process was something we had never seen, so we decided to take F792 into captivity, with the primary purpose of watching her light up in the evening. Something else we never knew, was whether females light up and then find a suitable place to glow, or whether they get into place before lighting up. There was no scientific emphasis applied to the observations and the notes were largely casual. It certainly proved very interesting though, but the following observations may not apply to the majority of females in a natural environment, or maybe at a different time of year (peak season).