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 will be overseeing 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 surveys glow worms; the survey’s findings are uploaded on to the UK’s official glow-worm database, and also help guide Cat’s management of the down.

The elusive creatures are attracted to this ‘island’ of Hampshire chalk downland because Cat’s grazing sheep and cattle maintain the open grassland, allowing female glow worms to crawl up grasses and glow from the top like tiny green beacons.

Only adult females glow brightly, to attract a mate. They live for just a few weeks. Once a female glow worm has mated, the glow will fade and she’ll lay her eggs, dying soon afterwards. But their larvae live for two years. 

Glow worm larvae live much longer than adults 
A glow worm larvae on top of a leaf
Glow worm larvae live much longer than adults 

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.

The survey

Stockbridge Down’s record survey so far was July 2016, identifying 237 in one night. The timing for the surveys needs to be spot on: 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. There are three different routes to survey, and the more eyes the better – though not too large a crowd, as this could affect ground-nesting bird sites. It’s seen as a novel volunteering opportunity; for many, it’s their first sighting of this magical green glow.