Lampyris noctiluca

Few sights on a British summer night match a glow-worm's cold green light in the grass. Only the wingless adult females glow, to attract the flying males, and they shine as soon as it gets properly dark from late May to early September, with a peak in mid-July. Look on open grassland and hedge banks rather than woodland; disused railway lines are prime sites, and the larvae need a supply of small snails. Walk slowly with a dim light pointed at your feet, then switch it off and let your eyes adjust. Avoid bright lamps: male glow-worms are drawn to artificial lighting, and most known sites are in dark places for that reason.