It produced an early start, at one time the prospect of an almost incredibly early end, Glow Worms in a survey section we thought would produce very little, seemingly unusually large numbers of males and a possible (but not surprising) link between temperature and predicting when the first Glow Worms may appear in Spring.

The 2017 season in brief

Overall, the season lasted from recording our third earliest ever female Glow Worm on May 20th, before finally ending on July 27th and producing a total of 273 females from six survey sections.

Our late afternoon and early evening larval surveys of sections A, B, C and D commenced on March 9th, with the first two larvae being recorded a few days later on March 14th. If you are new to reading our summaries, these four sections form a long grass strip, bordered on one side by a cycle path, on which wandering, pre-pupating larvae can be found during the early Spring months.

By April 8th, a pleasing total of 38 larvae had been recorded, measured and released, so we were quite hopeful for a good season. There was a change to much cooler weather during the second half of April, meaning we didn't conduct regular larval surveys for the rest of April or May, so the larval data produced this year is limited and not really of very much use.

As the season continues into July and August, hunting larvae producing short duration glows are found with increasing regularity. 2017 proved to be exceptionally poor for finding larvae after dark and we recorded glowing larvae on just two occasions between May 18th and July 31st.

On the other hand, we fared quite well in finding glows which (on closer inspection) turned out to be from newly formed pupae. We have found pupae on a number of occasions over the years, always found glowing after dark, when they are either freshly formed, or when they have been disturbed by a potential predator.

We had hoped to find the small Staphylinid Alaobia scapularis (Sahlberg, 1831) which is well known for its association with Glow Worm larvae. The only previous Nottinghamshire record for A. scapularis we know of, is of two we found with a female Glow Worm pupa at Clipstone Old Quarter on May 30th 2013. So we were delighted on the following evening, when we were fortunate enough to find another female pupa glowing along Section M and that two Alaobia scapularis were in attendance.

Both evaded capture, so the pupa was located to a safer site underneath a stone and left, hoping they (or others) would return. We continued to check the pupa on subsequent nights, in an attempt to secure a specimen for photographing and after missing a third A. scapularis on May 27th, we were eventually successful two evenings later.

Seasonal variations have tended to produce very mild Winters in recent years, often with a short spell of snow or icy conditions. The past couple of Winters have barely produced a frost here, let alone any snow and we once again experienced yet another very mild Winter, which developed into a cool and dry Spring - almost a carbon copy of early 2016. With a number of Glow Worm larvae appearing relatively early this March, it began to look promising for a potentially early start to this year's glowing season.

Before Spring 2017, a look at the average monthly minimum and maximum temperatures for the years 2008-2016 in Fig 02, showed that previous early glowing seasons followed when the average minimum temperature for the period January to April was 3.5°C or above.

This also applied when the average maximum temperature was above 10.5°C for the period January to April for the same two years.

The 2017 Glow Worm season in more detail

We were again unable to survey the whole site each night and restricted ourselves to surveying sections (in order of completion) O, L, M, K, J and D. Our former survey route was well over 6km long, had 18 sections (A to S) and took us around two hours to complete most nights. It became impractical for us to do anymore and this year, we had to omit sections of A, B and C, which are pretty much un-surveyable now through large areas of encroaching Bracken and Bramble.

The felling of Clipstone Old Quarter's last two large areas of Pine began in late August 2016 and by mid-September, there were huge timber stacks lining the track sides, which were held off the ground by timber supports.

We knew that there would be damaging implications to both Glow Worm habitat and Glow Worm larvae along Sections O, L, K and J, and we were at least able to monitor the immediate effects of what turned out to be a combination of Pine felling, timber extraction, timber stacking, forest track widening and spoil spreading.

Although we surveyed Sections L and M each night in 2017, the data from these sections is not included in the analysis that follows later. This is due to the lack of coverage in 2015 and not surveying either Section L or M in 2016. Despite the gap in coverage, having data from these sections between 2010 and 2014 and knowing the Glow Worm population from both sections, does mean that we have the knowledge to come to certain conclusions. We can say without doubt, that the Glow Worm population along Section L was severely affected by felling, timber extraction and stacking in 2016 and 2017.

The work effectively removed all larvae and all but a single female Glow Worm from almost the whole length of Section L, but certainly from where Pines were removed and the ground was prepared for timber to be stacked prior to removal. The timber stacks had been removed some weeks prior to surveying and in the above photograph, Glow Worms were only recorded from a point past the furthest end of the timber stack on the left hand side. Several females were found this end of both stacks and from behind where the photograph was taken, but these were actually just in the adjoining sections of O and K.

Interestingly, most female Glow Worms were recorded glowing from the western-side of the track running through Sections K and J, which we think may be due to female larvae selecting the most open aspect from which to glow from as adult. Females obviously favouring one side of a track, is not something we have noticed before.

Section K was the location for the first female Glow Worm (F001) of the 2017 season on May 20th, being found nine evenings after we began surveying for adults on May 11th and three days after predicting that the season could be an early one.

We'd expected the Glow Worm population in Section O (above) to be decimated through track widening and the creation of a new turning point for lorries removing the timber near to Peafield Lane. Most of the Birch and other young trees had been removed down the whole length of one side of the track in Section O, and there were large amounts of spoil that had been spread. We thought that the one area of deciduous trees bordering this section, would offer us our best chance of recording Glow Worms along this section in 2017, as this was virtually unaffected by the forestry operations. But we were surprised at how some Glow Worms had survived the felling and extraction in other parts (good numbers in one small area), while we recorded just one female from what we thought was likely to be safest.

Section O has often been one of the later sections to become active at Clipstone Old Quarter, with females appearing a good two weeks later than the traditionally early south-facing sections. Female F003 was certainly a surprise to us on May 23rd and like most females found along all the forest tracks this year, was found well away from the path edges and just about on the limit of spoil spread from track widening.

An unusual feature of the season, was that only a handful of females were present for longer than a week. These either remained unmated, as in the case of females F009, F261 and F272, or started glowing for a second time (F078, F093 and F230) following a prolonged period of absence. F093 was interesting, as she reappeared for her second night on June 16th, eleven nights after first glowing on June 5th.

Vegetative encroachment has assisted the decrease in the number of females being found along the path edges in this section. We had noted the decline in previous years, so larvae searching for a suitably open pupation site, now have to wander even further away from tall vegetation than they did a few years ago.

Sections K and J are similar by habitat and have tended to fare equally similarly most years. However, both sections occasionally show large changes in population counts some years. In 2012, both suffered large drops in the number of Glow Worms with produced counts dropping by 89% in Section K and 58% in Section J. We found that although the Glow Worm populations in sections O, K, J and D during 2017, were more or less in line with levels averaged over the past number of years, their numbers are still declining at Clipstone Old Quarter.

In order for there to be any prolonged peak, there has to be a build up of un-mated females over successive nights, in addition to a supply of freshly emerged females. Therefore, the contributing factor towards the low numbers of females in 2017, was that the biggest percentage of them were being mated on the first night glowing.

Following the change in survey route and survey sections/order, we often walked along Section O for a second time on return back to the car. This was usually much less than an hour after first starting our survey.

In many cases, females recorded on the way up had already gone 'lights out' by the time we returned and if they were still lit, they had usually attracted males. The season soon became talked about for what seemed to be larger than average numbers of males being found by recorders. We often remarked on the number of males ourselves during our surveying, thinking at the time that it was an unusual.

Fig 07 on the left, shows the percentage of 'one night' females in 2017. The second column shows the inclusive dates of the numbered females and the total number of 'one night' females per 50 females involved is shown in column three. The resulting percentage of females mated on the first night is then given in column four.

Peak numbers of males came during late May and June 10-25th and 86% of females mated on their first night is indeed a high total, but not the highest we have recorded here (92% in 2011) and only just above a similar 84% in 2010. In terms of actual numbers of males with females, we recorded 71 males with females in 2017, compared to 38 males with females in 2016 and some 90 males with females in 2014. The highest numbers of male Glow Worms recorded with females came in 2010 and 2011.

The number of males was the subject of many conversations between Glow Worm enthusiasts on social media. But the percentage of 'one night' females proved similar to three other seasons at Clipstone Old Quarter, despite us thinking to the contrary. In the end, what had seemed to be very high numbers of males wasn't really that unusual based on our own records.

Through years of monitoring and surveying, the Glow Worm population at Clipstone Old Quarter has been found to be in a steady decline. The cause is hard to narrow down to any single factor, but forestry operations such as felling and timber extraction etc, and site management such as herbicidal Bracken control etc, are especially damaging to invertebrates such as the Glow Worm. Our biggest concern for Glow Worm populations in Sherwood Forest, is the increased likelyhood for sites to become too dry through tree felling and thinning.

Results from survey sections O, K, J and D (in order of surveying) since 2010 follow, showing how Glow Worm numbers recorded within each section have fared over the years.

It seems likely that Glow Worms can survive forestry operations in just enough numbers, so as to maintain a viable breeding population.

After operations have ceased, there is the possibility that Glow Worm numbers have been affected so much, that populations gradually become more fragmented and isolated, especially with a succession of poor breeding seasons, or if there are naturally fewer males around in some years.

In the past few years, we have found very small numbers of Glow Worms in neighbouring plantations. These have been near enough to Clipstone Old Quarter to presume that at one time, they would have been part of a larger population covering a much larger area of the forest than they do now.

Having a smaller survey area, does occasionally allow us the time to survey new areas near to Clipstone Old Quarter, or in the Sherwood Forest area in general. As mentioned, we occasionally find Glow Worms in previously unknown areas and in 2017, found two females in locations that effectively linked a small population along the edge of woodland to the Clipstone Old Quarter population. The locations of these (and other recent records) are shown in blue below. The arrowed red lines mark the limits of our former survey area, along which Glow Worms were recorded.

Martin and Ludwik had negative results from previously reported Glow Worm sites at Robin Hood Hills, Nomanshill Wood, Thieves Wood and Rob Lane, and potential sites at Annesley Woodhouse Quarry and nearby Bentinck Banks SSSI. Thankfully, they did record Glow Worms from new areas of Harlow Wood.

We unsuccessfully surveyed an old Glow Worm site at Thoresby Park, but did find two females and a larva on heathland at Budby South Forest, which increased the range of a known population at nearby Swinecote Road, Budby and may actually be the correct location for historical records listed as Budby dating to 1929.

Below is the complete list of sites surveyed for Glow Worms during 2017. Those sites producing Glow Worms are highlighted in blue. Negative site visits are in grey.