How to spot glow-worms in summer hedgerows

Why glow-worms light up British hedgerows

On a still, warm evening in late June or July, a British hedgerow can look as though someone has dropped a handful of tiny green emeralds along the verge. Those pinpricks of light are almost always female glow-worms, and they are one of the most magical sights our countryside offers. Despite the name, they are not worms at all but beetles — the females of Lampyris noctiluca, a species that has become increasingly scarce in Britain over the past fifty years.

The female is the one doing the glowing. She is wingless, flat, and about the length of a thumbnail, and she climbs up a grass stem or low hedge twig after dusk to advertise herself. That steady, cold green light — often described as lime or apple-green — is a chemical signal produced in her lower abdomen. She will glow for two or three hours after sunset, hoping a flying male will spot her from several metres away. The males are winged, dull brown, and rarely glow themselves.

When and where to look

Timing is everything. Glow-worms need warm, humid, still nights, so the best conditions are those muggy evenings after a sunny day, when the air temperature stays above about 15°C and there is barely a breath of wind. Peak glowing usually begins around an hour after sunset and can continue until well past midnight, though 10pm to midnight is often the sweet spot.

The season runs roughly from mid-June to early August, with the strongest displays in the first three weeks of July. Look for:

• Rough, unimproved grass verges alongside lanes and footpaths
• The base of hedgerows, especially those with a tangle of tall grasses and brambles
• Old railway cuttings, churchyards, and unsprayed field margins
• South-facing slopes where the ground has baked warm during the day
• Anywhere with long grass left standing through the summer — verges that get flailed in June are hopeless

Glow-worms dislike fertiliser, pesticides, and close mowing. A hedgerow with a rough, unkempt skirt of grass beneath it is far more promising than a tidy one with a strip of bare earth.

Light discipline: the one rule that matters

If you take nothing else from this article, take this: never sweep a white torch along a hedge when you are looking for glow-worms. White light destroys your night vision for up to twenty minutes, and it also disrupts the beetles themselves. A female who is spotlit will often stop glowing and tuck down into the grass, and a male searching for her can be thrown off course completely.

Instead, give your eyes a good fifteen to twenty minutes to dark-adapt. That means arriving while there is still a little colour in the sky, walking slowly, and resisting the urge to check your phone. Once your pupils have opened, a single glow-worm will stand out from ten or fifteen metres away, and you will start to see dozens where at first you saw none.

If you genuinely need light to move safely, use a red filter over your torch. Red light has far less impact on night vision and on the beetles. Better still, let your eyes do the work and keep the torch in your pocket.

How to search a hedge without disturbing it

Move slowly and stop often. Stand still for a full minute at a time and scan low along the hedge line, letting your gaze drift rather than fixing on one spot. Peripheral vision is more sensitive in the dark, so look slightly to the side of where you think you saw something and the glow will seem to brighten.

Walk the same stretch in both directions — glow-worms are often easier to spot on the return pass when your eyes have fully adjusted. Keep your voice down and your footsteps soft; you will see more wildlife of every kind if you behave as though you are the guest, not the audience.

Do not handle the glow-worms. A female who is picked up will often stop glowing and may not resume for the rest of the night, wasting one of her few remaining chances to attract a mate. Admire her from a respectful distance, then move on.

Other nocturnal life in the same hedgerow

A summer evening at the hedge is never just about glow-worms. Sit quietly for half an hour and you will almost certainly encounter:

• Bats — pipistrelles are common along hedgerows, hawking for midges in the fading light
• Hedgehogs, rustling through the leaf litter at the base of the hedge
• Night-scented flowers such as honeysuckle and meadowsweet, which attract moths
• Large yellow underwings and other moths, drawn to the same warm, still air that glow-worms favour
• The occasional tawny owl calling from a nearby oak

Moths matter here more than you might think: glow-worms and moths share the same habitat, and both are in decline for the same reasons — light pollution, hedgerow removal, and the loss of rough grass margins.

Recording what you find

Glow-worm numbers have crashed across much of Britain, so every sighting is genuinely useful. Note the date, the time, the weather, and roughly how many glowing females you saw. A short walk along the same lane on several evenings through July will give you a surprisingly good picture of the local population. Pass your records to your county wildlife trust or local records centre — they use this kind of casual data to argue for protecting verges from untimely flailing.

Take a flask, wear long trousers against the nettles, and give yourself a whole evening. The glow-worms will not be rushed, and neither should you be.