The Mysterious Lesser Glow Worm

Reprint of an article that appeared in the Summer 2009 Edition of Common Ground.

Some members may have read in the Council’s free magazine about the recent discovery on Rusthall Common of a male lesser glow worm, one of Britain’s rarest and most elusive insects. Members of the glow worm and firefly family are more characteristic of warmer climates, and there are only three species on the British list, one of them apparently extinct since Victorian times. By far the most widespread is the well known common glow worm. Thanks to the prevalence of artificial light, and people’s fears about walking at night in unlit places, it is not often seen. But it does occur in a number of places around Tunbridge Wells and has been known for some years from Rusthall Common and the adjacent Beacon Hotel grounds.

The lesser glow worm is, as its name suggests, much smaller than the common glow worm. Its light is also less strong, consisting of two tiny greenish white ‘tail lights’ at the end of its body. On the other hand, the males are active during the day, which probably evens the chances of finding it if it is present. They are most likely to be seen in mid summer wandering over bare sandy ground such as footpaths and banks. While common glow worms feed on snails, lesser glow worms have recently been found to feed on earthworms, a type of prey many times larger than themselves.

Since its discovery in 1868, the lesser glow worm has been seen on only a few occasions in Britain, and until now only twice since 1961. It therefore has the highest ranking – red data book 1 – in the national list of rare and endangered species. Apart from a single record in Surrey, all previous examples have been found either in East Sussex or Hampshire. As Rusthall Common is close to the county border, the species’ presence there fits in well with the older pattern of records from East Sussex localities like Ashdown Forest.

What remains to be discovered is how strong the Rusthall population is. Several return visits failed to reveal any more, and further investigation will now have to wait until next summer. The only other currently known colony is on a private nature reserve near Southampton. The owner has offered to help in searching Rusthall Common, maybe bringing a live female specimen along in the hope of attracting males. This technique is known to work with many other insect species where the males are attracted by the female’s scent.

By Ian Beavis.