The Glow-worm - Ver luisant - Latin - Lampyris noctiluca.
If there is a warm evening and as the sun sinks beyond the hills, you may well see the pale green lights of the glow-worms shining from the long grass of the roadsides. If you leave your window open and yet protect yourself in bed from the biting midges with a bed net, you may see the same green lights shining above you from beetles which have landed there. Those in the grass come from the female creature and those on the net from the male. The sexes are so very different in form and habit that you would be excused for imagining that they are different organisms. Moreover neither are worms nor look like worms.
The female looks a little like an extended woodlouse. In the picture you can see one close to its food source, a snail. It is about two cms. in length, and as with most insects has six legs. At the rear end is an elaborate sucker used for locomotion; its legs aren't much use. The under side of the hindmost segments carries light making organs. The creature can turn these on and off at will. If it is in a state of 'passion' then it is reluctant to turn them off. The tail is then upturned so that the light is seen from above.
The males look like normal beetles. The photo shows a number, some of which I very much regret died and fell to the bedroom floor. Those on their backs show the enormous eyes which almost meet on the underside. They appear as two large black 'headlights' under the head. The mouthparts are almost squeezed into nothingness between them. On the topside, the eyes are provided with shades, easily seen in the centre beetle of the photo. This ensures that the beetles will respond to the beckoning lights from the females in the undergrowth and not attempt to mate with the moon. But why do the males have a glow? It would seem that the messages are signalled both ways. Perhaps the females become even more switched on when males fly overhead.
There must be large numbers of these beetles, at least, chez nous. Great numbers of males come into the house at dusk. Yet I see the females far less commonly. The males are attracted to all kinds of lights. It cannot help to conserve these beasties for so many to succumb to the huge numbers of lamps provided by man!
The larvae and females eat snails. They manage to paralyse the prey with a small nip and injection on the edge of the flesh. Then gradually they inject a dissolving enzyme. The resulting juice is sucked back. A snail can last some time, maybe one is enough for life. The adult males probably do not feed. The exceeding commonness of the species is a mystery to me. How can they spread when the females cannot fly? I have in these articles previously commented on the wonder of the spread of flightless females of various species.