The UK Glow worm Survey Home Page

Glow worm picture
Glow worm, Lampyris noctiluca. Photo copyright Robin Scagell

Glow worm and noctilucent cloud

Glow worm, Lampyris noctiluca, bottom centre, and noctilucent cloud in the background.
Little Marlow gravel pits, 14 July 2006. Photo copyright Robin Scagell

On this site you will find

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The UK Glow worm Survey
The UK glow worm survey began in 1990. It is run by Robin Scagell, and has no official status, funding or affiliation, but exists solely to gather information about a fascinating insect that most people don’t even realise exists in Britain. Information comes mostly from members of the public who see glow worms and want to know more about them. Before the survey started, it was said that there were fewer than 100 sites where glow worms could be found in the UK. The survey has shown that there are in fact hundreds of sites throughout the UK where they can be seen, and more sites are reported every year. Please note that we never give out or list details of glow worm sites on private land, other than to bona fide researchers, so if you have glow worms in your garden please tell us without worrying that you will get hordes of unwanted visitors in the dead of night! You can report a site to us by post or by filling in an online form. If you don't wish to give your home address that's OK, but an email address is appreciated so we can contact you if necessary. We do not send out any junk mail or sell address lists! Oh, and please don't send any pictures without prior arrangement – too many can overload my mailbox.

The survey has been publicised in particular by the Weekend Telegraph (July 2006), National Trust magazine (Summer 2005), BBC Wildlife Magazine, on BBC Radio 4, and by BBC TV’s Country File.

About glow worms

Key glow worm facts:
  • Only adult females glow, to attract the flying males
  • Adult glow worms can't feed, so they can live only for 14 days or so†
  • Once a female glow worm has mated, she turns out her light, lays†eggs and dies
  • Leave glow worms where they are – they know best where they like to be
  • Don’t take glow worms home – they need specialised habitat
As we travel in our cars from one brightly streetlit area to another, we are unlikely to notice the tiny lights of glow-worms, about as bright as an LED indicator on a hi-fi. Yet they are still to be found, and they may be more common than you think. But despite surveys over the years, researchers are still in the dark over the factors affecting the decline of glow worms, and even if they are declining. What is needed is the widest possible survey of the remaining glow-worm habitats, which is where you can help.

The glow worm, Lampyris noctiluca, is not at all worm-like but is a beetle up to 25 mm long. Only the wingless female glows strongly, to attract the flying males. Each individual female has an adult glowing life of only a few weeks until she mates, since she dies soon after laying her eggs.

After a few weeks the eggs hatch into larvae, and they remain as larvae for one or two further summers, feeding on small snails which they apparently paralyse before sucking them empty. The two- or maybe even three-year gap between a mating and the subsequent appearance of an adult helps to explain why you may find plenty on a site one year, yet few or none at all the next. And, of course, sites where they seem to have died out can’t be written off on the basis of a single night’s search.

The adult female and larva look very similar at first sight, but the larva has very obvious light spots on the rear edge of each segment, while the adult female has a completely black back with just a thin paler line down its centre. The larva has only a small†light-emitting region on the underside of the final segment, which appears lighter, while in the adult female the final two rear segments glow and are lighter in colour. The adult male has black wings. You can see these differences in pictures in the gallery.

Where and when to look

Where should you look for glow worms? Though they are said to favour chalky or limestone areas, they have been reported†from many areas of Great Britain. The peak glowing period is evenings in June and July. People are often surprised to discover glow worms in gardens, hedgerows or railway embankments where they had never been noticed before. Disused railway lines are prime sites, in fact. Glow worms can also be found on cliffs, woodland rides, heathland and even valleys in Wales or Scotland which meet none of the above criteria! There are few counties in the UK where they are not found somewhere, though they are believed to be absent from the Isle of Man and Ireland.

Having said that, I have had a report from Greystones, south of Dublin, which is awaiting more recent confirmation. In 2009 I received a report that glow worms can be seen in the Wicklow Mountains but a request for confirmation to the Wicklow National Park has so far gone unanswered. And in 2009 I also heard from Richard Fisk, who spotted what looked like glow worms at Killilane near Rosslare. We really need verification of these reports by means of a photograph of the actual insects, so anyone in the southeast of Ireland is requested to keep their eyes peeled and a camera at the ready.

Click here to see the latest UK distribution map published by the Biological Records Centre, which is the official recording centre for all UK species. For a more detailed map, see below.

You can read an updated list of the latest site reports received in 2009 by going to

There is also a list of UK sites in the 1992 report, or in the county-by-county lists, which I'm afraid I have not updated through lack of time and the requirement not to include recent sites on private land. Some people like to keep glow-worm sites secret, for fear of the ‘egg-collector’ mentality, which I appreciate. But I believe that it’s better to educate people that glow worms are best left alone rather than taken in glass jars to entertain the kids, and the sites that are well-known and feature in glow-worm walks do not suffer any obvious problems. There are far greater threats to them from ignorance and from lack of knowledge that the glow worms are there.

Wherever you find small snails, though unfortunately not the large common-or-garden variety, it’s worth looking for glow worms. They prefer open grass or hedges to woodland, but rarely are they to be found on land which has been ‘improved’ for agriculture. Look for them from late May to early September (with a peak in mid July), as soon as it gets dark. They glow for a few hours at a time, and usually stop glowing soon after mating. If you do see glow worms, don’t disturb them and certainly don’t take them home as trophies, no matter how many there are on a site. Their continued existence at your site could be on a knife-edge. But a short look by torchlight will do no harm, and you may see the smaller, darker (and glow-less) male mating – perhaps even several on one female!

You may also spot larvae, particularly on dark, moonless nights. They glow much more faintly, and only intermittently, for a few seconds at a time. They are also not worm-like but have segmented bodies and six legs at the head end, quite similar to the adults. They do, however, sometimes help themselves along with their tails when moving, which makes them look a bit like caterpillars. You are more likely to see them on vegetation, searching for snails, than in the same areas as the glowing females. It is important for the survival of the glow worm to find the sites where the larvae live, since only about one per cent of its life is as an adult. Comparatively little is known about the preferred habitat of the larvae, so reports of them are always welcome. They appear over a longer time span than the adults, supposedly between April and October – probably whenever conditions are right for snails and slugs.

Click here from some more information (FAQs) about glow worms and larvae.

How they glow

The light from glow worms is cold, and is a form of bioluminescence. It is far more efficient than most light sources we are familiar with. It is caused when a molecule called luciferin is oxydised to produce oxyluciferin, with the enzyme luciferase acting as a catalyst in the reaction. Adult Lampyris noctiluca do not have the same control over the oxygen supply of many fireflies, which can switch their lights on and off in an instant, and take minutes to switch on or off. Larvae, however, have smaller light-emitting organs and can twinkle briefly. Male glow worms have the same ability, but it is rare to see them glow.

Management of sites

Some people have asked about the conditions for encouraging glow worms or breeding them. We still do not know why some colonies die out even though there are no obvious factors such as destruction of habitat, use of pesticides or herbicides, or strong artificial lighting of the site. Glow worms need a supply of small snails as food (we are working on the preferred varieties) and therefore a patch of vegetation where they can find the snails. They also need a comparatively open area where the females can display to attract a male in June, July and August. As they retire into the ground during the day, high mowing does not appear to affect them unduly and very long grass may actually not be very suitable.

However, my feeling (in discussion with a keen observer, Linda Worrall of Barrowden, Rutland) is that the best cutting regime is not to cut at all during the glowing season from the beginning of June till the middle or end of August. If cuts are vital they should be restricted to high cutting, so as not to get down to the insects which will be down in the understorey. A certain amount of hay lying on the top is preferable to raking it up, which would probably disturb the glow worms, but what you have to avoid is cutting in wet weather which will produce a thick mat of clippings that even the most determined glow worm will find it difficult to climb through at night.

The females may appear on footpaths and there is therefore a danger period during summer if the path is heavily used in the late evening while they are emerging to glow. There is not much that can be done about this other than getting people to walk in single file.

As for breeding them, this has been done with varying results. Even under favourable conditions there may be a high mortality. Do not carry home glowing females hoping that they will lay eggs, or even catch a female that has apparently been mated in the hope of hatching a brood. It is better to leave them in the wild.

Are glow worms declining and if so, why?

This is a tricky one. Probably their numbers are on the decline, but with so little accurate historical information to go on, it is hard to put numbers on it. Similarly, we can’t be dogmatic about the reasons for any decline. If you study one site over a period of years you find that numbers can vary wildly from year to year, and from place to place on the site. The obvious factors which suggest themselves are:

Decline or changes in habitat When you go to the sites in the historical county-by-county records (see below) you find that many have now been built on or have been ‘improved’ in some way (eg an open space has now been ‘parkified’ by the removal of weeds.

Use of pesticides and herbicides This is bound to have an effect on the prey of glow worms and on the insects themselves.

Artificial lighting This has increased in extent enormously since the 1960s and few landscapes are now free from light pollution. Even in country areas householders’ insecurity lights – pardon me, ‘security’ lights – blaze across wide areas. There is no doubt that male glow worms are attracted to artificial lighting of any colour and this must distract them from finding females. But without a detailed long-term site survey with accurate and consistent before-and-after results there is no firm evidence that this does cause a decline. However, most glow-worm sites are in dark areas and this suggests that lights do cause a decline.

Changes in land use Much of what was open downland (such as on the Chilterns and South Downs) is now no longer grazed by sheep, allowing them to become increasingly overgrown. Glow worms prefer open areas to dense undergrowth. The increasing amount of set-aside land may be a positive change in the short term, if there are glow worms nearby to colonise the area.

Recently we have become concerned that sheep grazing might not be as beneficial as we thought. In the past, both sheep and rabbits would keep the grass short, but rabbits are now often shot, leaving it all to the sheep. Sheep’s urine may be bad for snails, removing the glow worms’ food supply. We need to find sites where there are known changes in management and reliable counts of glow-worm numbers, to see if there is anything in this.

Parasites Recent work has suggested that on some sites, parasitic beetles may be seriously affecting the population of glow worms. We need more research on this.

Other UK glow worms

Virtually all the glow worms seen in Britain are Lampyris noctiluca. There is another species of glow worm in Britain, Phosphaenus hemipterus , which is vary rare and apparently seen only in parts of Sussex and Hampshire. A specimen was seen in 1995 in Sussex, the first since 1961, and a small colony exists on a private nature reserve in Hampshire. In 2009, a new site was found near Tunbridge Wells. The adult female is only 5-7 mm long compared with 15-25 mm for Lampyris (though bear in mind that the Lampyris larvae are often only a few millimetres long). Furthermore, Phosphaenus does not glow – so if the ones you see glow, they are the common Lampyris noctiluca. Should you suspect that you have found Phosphaenus please contact either Robin Scagell †or John Tyler immediately so that they can come and verify the identification. Please do not try and catch or kill Phosphaenus if you do see it. For more information, see this article by RaphaŽl de Cock, John Horne and John Tyler.

RaphaŽl de Cock has contributed a page showing how to identify the three main European species: the common glow worm Lampyris noctiluca, the lesser glow worm Phosphaenus hemipterus and the firefly Lamprohiza splendidula,found in mainland Europe.

False trails

There are other creatures that emit some luminescence, including caterpillars and centipedes, and fungi can also glow. See here for a photo of a geophilomorph centipede, for example.

Another cause of false reports of glow worms is actually light reflected from shiny leaves, dew or litter. It is therefore vital to check that what you see really is a beetle with the light coming from the final tail segments.

Finally, we get occasional reports of fireflies in Britain. As far as we know they do not exist in the UK, and it is probable that the reports refer to other flying insects seen in light beams. True fireflies swarm around a clump of bushes or in a glade or wood. If you do come across fireflies in Britain then make every effort to catch and keep one (dead or alive!) and let us know immediately. Fireflies are found in some places on the near Continent, and for a few reports go to the International section.

Latest reports

You can read an updated list of the latest site reports that I have received so far in 2009 by going to

2009 summary

Glow worms were reported unusually early this year. The first report came in on 15 May. Several people subsequently commented that they saw glow worms on their local site earlier than usual. It looks as though the season as a whole was a week or two early, though glow worms were still being reported in October. Quite why they†should have been earlier this year is unclear. Although the spring weather was good, May 2008 also had a hot spell.

However, one concern was the autumn drought in south-east England. There was little or no rain over a large area for about a month at a time when newlyhatched larvae would be looking for their first meal and later instars would be fattening up for 2010. This may mean poor numbers in 2010 and 2011.

If you saw glow worms this year, please do report them to me. If the site is on private land please say so. You need not give your personal details if you don't wish to, and the data collected is used only for the purpose of wildlife recording – we don't use our database for any other purpose, and certainly not for any mail shots.

As always, many reports came from sites previously unreported. Quite often these were single glows or just ones and twos spotted in gardens or roadsides. A large number are found near railways, including sites to the south of Edinburgh and in Solihull where glow worms have not previously been reported.

John Hume has taken a video of a pair mating at Ellerburn Bank, Yorkshire. Notice how at the end the female is starting to make her way down into the undergrowth, still glowing and carrying the male with her!

Glow worm evenings and walks 2009

All over for the year! Please let me know of any being organised for 2010.

Glow worm report and map of UK sites

I have produced two reports of the survey, in 1991 and 1992. These were sent out to those who asked for them at cost. I always intended to do more, and indeed started one, but I have not completed them. You can read most of the text of the 1992 report , which contains lots of anecdotes and comments on glow worms, as well as a UK map of where they were seen in 1992. So click on the link to see this 70k file.

There is now an updated map of the sites reported to the survey, as at 2006. It includes sites recorded on the database plus some reported to the BRC survey and placed only approximately. Please note that some sites for which we do not have accurate positions are simply recorded at the lower left-hand corner of their 1 km grid square and when they are near the coast they may appear to be out at sea, so please don't send in any quips about amphibious glow worms. It is available in two sizes: small, for viewing on your computer, and large (525 kB), for downloading, as the image may not display on your browser.

How you can help – the survey

If you have found glow worms, please let us know where you saw them as it will help us to chart the existing numbers and geographical distribution. An accurate grid reference to the site is really helpful to us, and online maps make it a simple matter to find it. We do not give out details of private sites to the public, so please do not worry that you will get people coming round to your garden at the dead of night to see the glow worms! You can either fill in the online form or just send me an email .† You need not give your personal details if you don't wish to, and the data collected is used only for the purpose of wildlife recording – we don't use our database for any other purpose, and certainly not used for any mail shots.

If you would like to take part in the survey, it’s probably best to start by finding glow worms on a known site (on public land) so you know what to look for. See the county lists for places to try. Then you could look around for similar sites in your area. Old railway lines are ideal sites, but any unimproved grassland (that is, unimproved by farming techniques, and with a variety of different vegetation) is worth a look. Go along after dark, with someone else for security, and take a torch so you don’t fall down rabbit holes and to help you make notes. (Avoid very bright lights or those fluorescent camping lights that destroy night vision.)

Glow worms start to shine as soon as it gets properly dark, which means around the time you can no longer see colour in the landscape by natural light. Count the glows you see (usually the adult females). If you plan to survey on several occasions it is a good idea to develop a standard route so that you are always comparing the same area, even if this means missing a few. Keep notes, and draw a sketch map of the area to help pinpoint where you saw the glow worms. Then fill in the survey form, either online or by printing out a copy.

The form may look detailed, but if parts of it do not apply to your site or are hard to fill in just leave them blank. Please give as accurate a site location as possible. It is important that we know exactly where glow worms are to be found so that changes can be monitored over the years. If you are unsure how to give a map reference, please click here for help.

Link to the survey form (thanks to Timo Newton-Syms for providing this updated e-mailable version). If you want a printable version, please click here.

Sites county by county

The first national survey of glow worms was carried out by the late Anthony Wootton of Country-Side magazine (the journal of the British Naturalists’ Association) during the 1970s. Members of the BNA were asked to send in records of sightings old and modern, and these were published in some detail. For a detailed set of these records, together with some more modern sightings that have been reported to me, click here . It would be very helpful if people could revisit the old sites during the glowing season, to help establish any decline (or indeed increase) in numbers.

NEW! County coordinators

If you are particularly keen on investigating the glow worms in your area or county, I am setting up a network of local coordinators who can follow up reports if necessary and undertake more detailed research. There is plenty that can be done even outside the summer glowing period – searching for old reports in local natural history records and even talking to the oldest inhabitants of villages who may remember seeing glow worms long ago. If you are interested in being a local coordinator, please let me know . These coordinators not duplicate the work of the existing county wildlife recorders, but could be the same people if they have a particular interest in glow worms.

Coordinators so far are for Wiltshire (Angie Chick), Cambridgeshire and Bedfordshire (Robert Geaves and David Savory), Gloucestershire (Denise Gibbons), Dorset (Barbara Smith and Jessica Thornton) and Essex (Tim Gardiner). Please contact the glow worm survey in the first instance to be put in touch.

The glow worm book

There is a book all about glow worms – the first on the subject in the UK. Written by John Tyler, it describes what is currently known about glow worms, and gives more information on how to find them. John has made a full survey of the literature on glow worms, and much of the information in it has never before been published in this country. It is fully illustrated in colour. By publishing it privately we are keeping the costs down. The new, fully revised edition , published April 2002 (76 pp paperback, A5 format) costs £10 post free. For a copy please write to John Tyler at 5 Woodfield, Lacey Green, HP27 0QQ, enclosing a cheque for £10.00 made payable to John Tyler. A few copies of the first edition (64 pp, published 1994) are still available at £5.00 post free, or you can read the text-only online version completely free.

Nick Moyes said of the first edition: ‘Excellently researched and privately published. Superb illustrations of all stages of their life cycle’ and who are we to argue.

For a much older account of glow worms you can now read online a partial translation of a classic chapter about the glow worm by the great French naturalist and writer Jean-Henri Fabre. The full chapter is available in the original French.†

Glow worms under threat†

Colonies are still under threat. Tony Haywood reports: On the 20th June 2005 I reported 24 glow worms at a site near Stafford. A visit last night to the site revealed a closure of the footpath/cycle-way. Repairs to holes in the path. It seems they have taken a sledge-hammer to crack a nut and have decimated the colony. Large areas of the grassy area containing nettle, rosebay and the habitat has been bull-dozed. Large piles of earth are ready to be spread,† and will probably cover what remains of the colony. 4 glowing females were there last night, they are in the path of work for next week I assume. If some-one had said,"I know where there is a colony of glow-worms, lets go and destroy it" they could not have been more accurate.†

†† Should† Stafford county council be aware of the site, and is there any legal responsibility that should make them undergo any such repairs with a little more care? I will try to contact the council department responsible first thing on Monday. I look forward to your comments.

Unfortunately, glow worms are no better protected than, say, woodlice. But often local authorities will make efforts to protect the colony if they know it is there, because of the great appeal of glow worms. However, you can't assume that they know about a colony. If you know of any colony in a similar situation, it is a good idea to advise the local council or the county conservation officer of its existence, as they should be consulted before any work is carried out. They may also need advice on how to protect the colony, in which case please refer them to me.†

In fact, Tony has now reported: The head†conservationist for Stafford county council made an immediate visit to the site and stopped work on the foot-path. Damage limitation was achieved. I await next years season with hopefulness.

Update June 2009: Tony reports that the colony has recovered, and 25 glows were seen.

Tidy churchyards = no glow worms † Simon Frogley has been studying the glow worms in the churchyard at Overton in Hampshire. He says:

They are down in number and size from 2002/3.† In 2002 I often counted over 90, and once 120 on any one evening.† This year the maximum I've seen has been 47.† However, I've been working with the vicar to try and get the policy† changed there – did a TV interview with him for Meridian and wrote an article for the parish magazine – it has become so tidy there, last year was the worst -- that there are few places left for snails or larvae.† The best area for them now is a bank where the grass is left, so that is where they are this year (for the first time in any quantity) but there is strong street lighting above them there.††Anyway, the vicar†is seeking support from parishioners to provide more cover in the areas that they used to favour, so that might help.

Pictures of glow worms

You can see a few more pictures of glow worms and colonies in our gallery.

Other people interested in UK glow worms

The UK national recorder for glow worms is Keith Alexander . All reports emailed to this site are forwarded to him, so please report them to me first.

The leading glow-worm expert in the country is John Tyler. He was previously warden of a wild fowl reserve in Sevenoaks, and is now a freelance naturalist.

Nick Moyes of Derbyshire County Museum is an enthusiastic glow worm hunter.†

Prof. Anthony Campbell in Cardiff is carrying out work on bioluminescence.

A continuing survey of Essex glow worms is being carried out by Tim Gardiner of Writtle College. Click here to download a copy of the report in Word 97 format (260 kb).

Alan Stewart at the University of Sussex is investigating 1) Visual sensitivity and mate searching behaviour of male glow-worms, 2) Factors affecting length of life-cycle and 3) Aggregative behaviour and group feeding in early instar larvae.

If you want to see what some of us look like, here are photos taken at recent gatherings!

There is now a Google Group devoted to glow-worm research in Europe at

International reports

Though our survey is really intended only for the UK, we are happy to receive reports of both glow worms and fireflies from other countries and will keep the records online . We do receive requests from other countries for information and it may come in useful in the future.

A survey of Spanish glow worms and fireflies is now under way, with extensive pages of information about glow worms in Spanish. See for more details.

" I found this†glowing critter in my backyard...." If you are in the US, sorry, we can't help you identify it but we know a man who can. Prof. James E Lloyd, Dept of Entomology, Bldg 970, Hull Road, Univ. of Florida, Gainesville FL 32611 has kindly agreed to answer such queries and you can contact him via his secretary. You can read some of his firefly newsletters online at Click here for a news story about Lloyd from the University of Florida.

Someone who is interested in glow worms in Belgium is RaphaŽl de Cock, who hopes to carry out a European survey. He is interested in the reasons why glow worms do glow, and believes that it may have originated as a warning mechanism, like the bright colours of some insects (aposematism). Contact him at Dieren Ecologie or visit his website:

Peter Stallegger of Association Faune et Flore de l'Orne carried out a survey of glow worms in Normandy in 2002. Visit his website at for details and maps of where they were to be seen.

Around Zurich, Switzerland, Stefan Ineichen is an urban ecologist investigating the survival of glow worms in the country areas around the city, and even in cemeteries and gardens within Zurich itself. With financial support they have started a GlŁhwŁrmchen Projekt which is using the insect ‘as an attractive flagship species to improve habitats and to get people connected with nature.’ He is studying the factors which affect the survival of the glow worm, and would be pleased to hear from anyone who wants to help. We look forward to seeing the website which he is preparing.

A survey in the French-speaking part of Switzerland was carried out 2001 by Centre Suisse de Cartographie de la Faune – contact Yves Gonseth for details. It was publicised through the magazine Energie-Environnement which is distributed free of charge to every French-speaking Swiss – about 880,000 people. The results were published in the December issue of La Salamandre; 900 observations were received from around 500 people. Some have seen glow worms at 2000 metres in altitude in the Alps. Click here for a more detailed report and map.

There is also a survey being carried out in Germany. Go to for full details in German.

You can find a wealth of information and research about US fireflies on the web pages of Terry Lynch. Find them at . This site gives masses of information about the rearing and preservation of the US firefly, Photinus pyralis, as well as many links for further info.

There is an excellent firefly page compiled by Donald Ray Burger in Houston, TX, USA, with many links. Find it at† Animaltrek site also has links to firefly pages.

Chip Fesko has contributed a poem about the fireflies he saw as a child which may hit an old memory with others.

In Nepal, Prem Bahadur Budha is researching fireflies but can find very little literature on the subject. If you have an interest in Asian firefly species please make contact directly. See his message on the International page.

Italy is well known for its fireflies but there seems to be a lack of literature on the subject. If you know of relevant papers or would like to be involved with a project to study them scientifically, please contact Giuseppe Camerini.

Further information

Please contact me if you want to know more about glow worms, provide a link or make a complaint. I am always happy to hear of other surveys and to see people studying glow worms. Help with the UK survey is always welcome – I am self-employed running Galaxy Picture Library and wish I had more time to devote to glow worms and to maintain a list of up-to-date sites! I am happy to report that Helen Johnson is now entering the information sent in using the MapMate software, so I hope that in future our records will be kept more up to date.

Site updated 3 November 2009
Visitors since December 2005