Glow worm surveys at Stockbridge Down

A glow worm on a leaf at night, spotting during surveys at Stockbridge Down, Hampshire

On a summer’s night, under the soft darkness of a new moon, our ranger Cat Hadler oversaw her fourth annual glow worm survey, aided by a team of enthusiastic volunteers. Stockbridge Down is one of just a handful of places in the country that officially surveys glow worms, but many people report sightings. According to the UK's glow worm database, nearly 300 different places recorded sightings of the neon green glow in June last year. Cat's results are uploaded on to this national database, but they also help guide her management of the Down.

The status of Britain's glow worms is poorly documented, but there is evidence to suggest severe population decline. The flightless females don’t move more than a metre or two in their adult life, so habitat fragmentation and loss is a real threat. That's why it's important we try to protect surviving populations of these much-loved beetles. 

Glow worms love chalk downland, but most of this has disappeared in the last century. They thrive on Stockbridge Down because Cat’s grazing sheep and cattle maintain the open grassland, which is essential to female worms, who crawl up grasses and glow from the top like tiny green beacons.


Glow worms in action at Stockbridge Down, Hampshire

Female glow worms climb up grass stalks before turning on their green light to attract a mate. Like a lot of our wildlife, glow worms' habitats have declined over the years, but they're currently thriving on Stockbridge Down in Hampshire.

Female glow worms onlly live for a few weeks. Once she has mated, the glow will fade and she’ll lay her eggs, dying soon afterwards. But their larvae live for two years. 

Glow worms generally prefer open, grassy areas that haven’t been treated with pesticides, as they or their food source may not survive the chemicals. The unimproved chalk grassland of Stockbridge Down is an ideal habitat, where their main food source (slugs and snails) can be found in abundance.

Glow worms cannot be attracted onto a site if they are not already nearby, so it’s vitally important that we monitor and protect our existing population.

Stockbridge Down is carefully managed to encourage wildlife
Undulating downland in summer with a chalk track running through it
Stockbridge Down is carefully managed to encourage wildlife

The survey

The June 2018 survey at Stockbridge Down recorded the highest ever figure – a record 119, compared with 48 sightings in 2017. Traditionally, July should have even higher, but in fact numbers dropped to 108. This may have been because glow worms were negatively impacted by July’s heat wave.

Cat’s surveys started at 10pm – glow worms like a late night! The date needed to be very carefully chosen too: females won’t glow under a full moon because they can’t compete with the light, and poor weather affects them, too. 

The task couldn’t be done without the help of volunteers, and an enthusiastic team braved the darkness of the Down to help. There were three different routes to survey, and although we needed lots of pairs of eyes, we made sure numbers were restricted, to protect glow worms and ground-nesting bird sites.

For some, the event gave them their first ever sighting of the eerie green glow - a memory to cherish, and which we hope they’ll enjoy again this year.