Essex Glow-worm Survey
however, some efforts have been made to ascertain its national distribution. The earliest of these was a survey conducted by the British Naturalists’ Association (BNA) in the 1960s and early 1970s. It was from this initial survey that a decline in the British Glow-worm population was first suspected; with many recorders noting an apparent fall in numbers. In 1991/92, a survey was launched by Robin Scagell http://www.glowworms.org.uk 
, with the aim of both revisiting the sites identified by the BNA survey and investigating previously unrecorded ones.
Photo: Mating Glow-worms, female being attended by winged males, credit Mike Wright
However, much of the evidence for a decline in the British Glow-worm population collected by the British Naturalists’ Association and the UK Glow-worm survey is anecdotal and long-term studies on the abundance of glow-worms on individual sites are rare. In an attempt to scientifically document any decline in the abundance of this species in Essex, the Essex Glow-worm Survey was initiated in 2001. As part of this survey, members of the public were asked to establish a transect at a known colony and to monitor the abundance of glowing females, using a standardised method, for a number of years.
A total of 2169 Glow-worms have been seen on 246 walks since 2001. The highest count was 101 Glow-worms at One Tree Hill in 2002. The average count of Glow-worms (each count was corrected for transect length at every site so all values are comparable between sites and years) in each year is shown in the chart below and we can see that there has been no short-term decline in numbers, indeed, 2007 was the best year by far, with an average of approximately 4 Glow-worms per 100 m. The lowest number of Glow-worms were seen, on average, in 2003, which may be linked to the drought conditions experienced in this year. Glow-worms may have desiccated prior to pupation, it is even possible that adult females may have died due to the hot, dry conditons.
If we look at individual sites in the chart below then it appears there are strong declines in Glow-worm numbers at One Tree Hill in Langdon Hills Country Park, and Manwood Chase in Abberton, which is extremely worrying as both had fairly high numbers in 2001. A population 'crash' seens to have occurred at Manwood Chase in 2003, perhaps this was due to the drought conditions and the death of pre-pupation larvae and glowing females due to heat stress/desiccation.
However, increases in Glow-worm numbers were recorded at Iron Latch Nature Reserve near Colchester, and Finches Nature Area in Canewdon (both managed by Essex Wildlife Trust).
It is hoped to continue the Essex Glow-worm Survey in future years to get a really long-term view of how Glow-worms are faring in the county. Potential threats to this species include habitat destruction/fragmentation and climate change. However, there is no reason at the moment to be too despondent about the status of the Glow-worm in Essex, overall numbers do not seem to be declining, and the species has been found at over 70 sites since 1992 and is widely distributed. The above text was mostly taken from an article published by Tim Gardiner in the British Journal of Entomology and Natural History published in early 2007.
The survey has already resulted in a number of publications in various journals. I include a brief summary of each publication below with full details should readers wish to read further.
General information on Glow-worms in Essex (distribution, habitats etc.)
Gardiner, T., Pye, M. & Field, R. (2002) Glow-worms Lampyris noctiluca L. (Coleoptera: Lampyridae) in Essex: results of the 2001 Essex Glow-worm Survey. Essex Naturalist 19: 151-159.
Abstract A countywide survey of the Glow-worm Lampyris noctiluca L. (Coleoptera: Lampyridae) was undertaken in 2001, which aimed to ascertain the current distribution of this species. The survey involved establishing a transect at a potential or known site and walking it three nights during the summer. In addition, casual observations of L. noctiluca were accepted so that the Essex distribution could be determined. The survey indicates a widespread but localised distribution for L. noctiluca, although this species is not as rare as previously thought, with observations having occurred at 43 sites since 1992.
Numbers of L. noctiluca observed on the transect walks were mostly low. The highest count of the survey occurred at One Tree Hill, where 76 individuals were observed. One Tree Hill is part of Langdon Hills Country Park, near Basildon and is of great importance for L. noctiluca in Essex, as 37% of individuals recorded during the transect walks were observed at this site. The preferred habitats were meadow and scrub, predominantly in dark, unlit areas. Few L. noctiluca individuals were recorded near any form of artificial lighting. The status of this species in Essex appears to be relatively secure in the short-term, although development pressure, pollution and neglect of sites are the main long-term threats.
Gardiner, T., Pye, M. & Field, R. (2003) The Glow-worm Lampyris noctiluca L. (Coleoptera: Lampyridae) in Essex. British Journal of Entomology & Natural History 16: 233-240.
Abstract During 2001 and 2002, a detailed survey investigating the distribution and abundance of the Glow-worm Lampyris noctiluca L. was undertaken in Essex. Only 13 records existed for this species within the county at the start of the survey, and many of these were old and gave imprecise location details. A simple transect method was utilised to ascertain the abundance of L. noctiluca at 12 sites, whilst records of this species since 1992 were collected to determine the current distribution in the county. The survey results suggest a widespread distribution of L. noctiluca in Essex and a large number of recorded sites, despite a lack of favourable habitat in the county. However, the transect survey data highlights the uncertain future for this species in Essex. Counts of glowing adult females on the transect walks were generally very low. Some of the smaller populations were isolated by several kilometres from the next nearest occupied site. These colonies are therefore most at risk from extinction, particularly as the available favourable habitat at these sites is limited.
Gardiner, T., Pye, M. & Field, R. (2003) The influence of soil pH on the abundance of the Glow-worm Lampyris noctiluca (Linnaeus) (Lampyridae) in Essex. The Coleopterist 12: 121-123.
Summary It is often stated in literature that the Glow-worm Lampyris noctiluca is restricted to calcareous soils where snails (its larval prey) are found in the greatest density and species richness. The abundance of adult female L. noctiluca was recorded at 16 sites in Essex using a simple transect method and was compared with the soil pH at these sites. There was no significant relationship detected between soil pH and the abundance of L. noctiluca, with this species occurring on soils with a wide range of pH (4.3-8.2).
Habitat management
Gardiner, T. (2008) Nature reserves and Glow-worms Lampyris noctiluca L. (Coleoptera: Lampyridae). Entomologists’ Gazette 59: 131-138.
Abstract The Glow-worm Lampyris noctiluca L. (Coleoptera: Lampyridae) is thought to be a declining species in the UK with habitat fragmentation causing isolation of populations and loss of genetic diversity, a problem which is compounded by the sedentary nature of larvae and adult females. Therefore, nature reserves may be particularly important refuges for this species in the Essex countryside which is increasingly threatened by development and agricultural improvement. However, this study reveals that the highest densities of glowing females are found on non-nature reserve sites which may be more prone to change through human activity such as building development or agricultural improvement than populations on nature reserves. Reasons cited for the low density of L. noctiluca on nature reserves are unfavourable management regimes such as grazing or the historical encroachment of scrub and succession to dense woodland with a sparse herbaceous understorey. Substantial opportunities exist for linking existing populations of nature reserve and non-nature reserve sites with linear corridor or stepping stone habitats to create a patchwork of interconnected colonies.
Gardiner, T. & Gardiner, M. (2005) Monitoring Glow-worm Lampyris noctiluca L. (Col.: Lampyridae) populations in grazed and mown grasslands. Entomologists’ Record & Journal of Variation 117: 263-266.
Abstract Glow-worms Lampyris noctiluca L. (Col.: Lampyridae) were studied in grasslands under varying management regimes. Meadows subjected to a single summer cut for hay supported smaller colonies than unmanaged sites although the reasons for this are unclear. Grasslands mown regularly throughout the summer showed an increase in numbers of females; it is theorised that this might be a consequence of favourable adjacent habitats and that the shorter sward provided advantage to females displaying to males in flight overhead. A mosaic of regularly mown and tall unmanaged grassland may provide the ideal habitat. Grasslands subjected to grazing by cattle or rabbits supported only small colonies.
Changes in abundance over time
Gardiner, T. (2007) Short-term changes (2001-2005) in Glow-worm Lampyris noctiluca L. (Coleoptera: Lampyridae) abundance in Essex. British Journal of Entomology & Natural History 20: 1-7 .
Abstract There is much anecdotal evidence to suggest that the UK Glow-worm (Lampyris noctiluca) population has declined in the last 50 years, but there has been little scientific research to confirm this. The Essex Glow-worm Survey commenced in 2001 with the aim of documenting changes in the abundance of glowing females using a standardised transect counting procedure. Results from the first 5 years of monitoring on 12 transects suggest that L. noctiluca is declining at 6 sites and increasing at only 3. Indeed, Glow-worms appear to have disappeared from one site where no females have been seen since 2001. Worryingly, the number of females seems to have declined significantly at two sites which had high abundance in 2001. One possible reason for these reductions may be low spring rainfall which may lead to desiccation of larvae and scarcity of larval food (snails and slugs) in the pre-pupation ‘walkabout’ phase in dry and hot years such as 2003. It is hoped to continue the survey in future years to determine whether Glow-worms are declining in the long-term.
Gardiner, T. (2007) The decline of the Glow-worm Lampyris noctiluca in Epping Forest. Essex Naturalist 24: 90-92 .
Summary Anecdotal evidence suggests that the Glow-worm is declining in Epping Forest, an area in which it was common up until the 1930s. However, since WWII records of large numbers of Glow-worms in the Forest are rare and the possible reasons for the apparent decline of the species are reversion of open areas to scrub and woodland due to a lack of grazing and air pollution. However, grazing has been reintroduced to the Forest and air pollution levels appear to be decreasing so it is hoped that Glow-worms can make a comeback in the area.
Development of transect walking methodology
Gardiner, T. (2006) Does the phase of the moon affect Glow-worm Lampyris noctiluca L. (Lampyridae) counts? The Coleopterist 15: 92.
Summary Full illumination of the moon has seriously affected the number of glowing females that observers have been able to record in the Essex counts. Anyone wishing to see large numbers of glowing females or to undertake standard, comparative counts is advised to avoid searching on nights with a full moon.
Gardiner, T. (2006) Effect of survey start time on counts of the Glow-worm Lampyris noctiluca (Col.: Lampyridae). Entomologist’s Record & Journal of Variation 118: 184-185.
Summary It seems it is crucial that criteria for surveying glowing females reflect the earlier sunset and ‘lighting up’ times (of females) in late July/August. Surveys in late July/August should start as close to 2200 h as possible to avoid low counts of glowing females (see figure below from paper). It is also important to remember that the light level needs to have fallen sufficiently (e.g. difficult to make out colours) before females ‘light up’ and the survey can commence.
Gardiner, T. (2007) Optimum survey dates for detecting Glow-worms Lampyris noctulica Linnaeus (Lampyridae) in Essex. The Coleopterist 16: 12-13.
Summary When the Essex Glow-worm Survey was initiated in 2001 it was believed that transects counts of glowing adult females should be undertaken in July and early August when most females would be displaying. As the survey has progressed it has become apparent that female numbers may be higher in late June/early July and that the counts were being undertaken too late in the glowing season. Therefore an extra walk period (25 June-8 July) was added in 2006 and proved an instant success as most Glow-worms were seen in this two-week interval, numbers were much lower on the following transect walks (9 July-19 August).
Gardiner, T. (in press, volume and page numbers to follow) Observations on the incidence of adult male and larval Glow-worms Lampyris noctiluca L. (Lampyridae) whilst transect sampling. The Coleopterist.
Summary A total of 23 males and 46 larvae were recorded from 8 transect sites (from 2001-2006), which is a ratio of approximately 2 males and 4 larvae for every 100 females counted indicating that both life stages are infrequently seen whilst transect walking.
Gardiner, T. (2006) Glowin’ in the rain. Bulletin of the Amateur Entomologists’ Society 65: 146-147.
Summary It has become apparent that counts of glowing females may actually be higher on nights with either drizzle or heavy rain than those where it was not raining. One possible explanation is that adult males may not fly when it is raining. Therefore large numbers of glowing females, which ‘switch’ their light off after mating, may be observed on wet nights as there are no patrolling males to mate with.