It was late one cloudy summer's night. As the skies darkened over the fenland reserve, the tall, shadowy figures of mallow, hemlock and sow thistle emerged. Common and soprano pipistrelles soared overhead, an exciting first encounter for younger members of the group, but this wasn’t what they were searching for. Suddenly in the darkness ahead, a small green light began to glow. The group hurried forwards eager for a closer glance, cameras appeared, smiles widened, and a sense of wonder filled the air. Laying right at their feet, beneath the ferns here in the Great Fen... a glow-worm!

Actually... 60 glow-worms (57 females and 3 males)!

On 12^th July, Laura and Rebekah lead our second glow-worm walk (the first being in 2023 with 102 females recorded) at New Decoy in the Great Fen. Starting off in the picnic area, the group enjoyed hearing about the interesting life of a glow-worm, the importance of the Great Fen for providing habitats for them and the potential threats they face across the UK.

There are two species of glow-worm in the UK (common and lesser glow-worms). Being smaller and less reliant on glowing, the lesser glow-worms are harder to see and therefore easier to miss. For this walk, we were searching for common glow-worms which have been recorded by volunteers in the Great Fen since 2022.

Common glow-worms start life as small pale-yellow eggs which can glow (incredible but very rare to see!). After approximately 35 days, small larvae emerge which are dark in colour with a reddish spot on each of their segments. The larvae are specialist eaters with an appetite for slugs and snails. Once they find their prey, they bite them, piercing the skin and injecting poison. In the case of snails, the glow-worm larvae may jump on their shells to go along for a ride whilst they wait for their meal to be ready... The snail or slug gradually becomes paralysed and eventually it turns into a soupy consistency for the larvae to suck up (this sounds rather messy... but luckily the larvae have developed a small brush-like device at the end of their abdomen to allow them to clean up after a meal!).

Glow-worms spend one to two summers as larvae, shedding their skin as they grow before pupating. Once they emerge as adults, the female remains similar in appearance to the larvae, but they have lost the spots on the edge of each segment. Females are flightless, relying on their glow to attract a male. To ensure the flying males see her green light amongst the vegetation, females will climb to the highest point available (which is often up grass stems) where she curls her body to project the glow towards the sky.

As adults, they have no mouthpiece, meaning they live for only a few weeks and are running on limited energy supplies. The pressure is really on! For the glow-worms who mate successfully, the female’s glow will go out and over the next few days, around 100 eggs are laid. The cycle begins again...

Did you know?

Not many places today are free from light pollution, however the Great Fen has been awarded the designation of a Dark Sky Discovery Site by the Science and Technologies Facilities Council at two sites, The Wildlife Trust Countryside Centre and New Decoy Farm Information Point.

Dark skies make the Great Fen a fantastic place to be if you are a glow-worm, as the lack of artificial light makes it easier for females to be found by the males. It is also a fantastic place to visit if you are looking to see glow-worms too! Thank you to everyone who joined us on this guided walk. Your tickets and Wildlife Trust memberships ensure we can continue to create new habitats, defend nature and work for a Wilder Future across our counties.