Gardeners have been urged to pick up their torches and hunt in their gardens for slugs as the Royal Horticultural Society issues a plea for data on the disappearing British bug.

There are worries the Yellow Cellar Slug, which is useful for gardens as it feeds on decaying rather than live plant material, is being usurped by the Green Cellar Slug, originally from Ukraine, which arrived in the 1970s.

Since the Green Cellar Slug arrived, numbers of the useful slug are thought to have sharply declined.

While both slugs have large, green-yellow, patterned bodies, the Yellow Cellar Slug has a long yellow stripe running along the centre of its tail.

As slugs are nocturnal, people are being asked to don torches and step out into their gardens after dark in the hope of recording them.