GLOW-WORMS G . D . HEATHCOTE
THE British Naturalists' Association recently published a report (1971) on a survey made of the distribution, both past and present, of the glow-worm, including a distribution map prepared by the Henry Doubleday Research Association and the Nature Conservancy from observations made in 1966. The number of glowworms appears to be decreasing, and there are few records from Suffolk, but this may reflect the limited number of entomologists reporting their occurrence and not their scarcity. However, the glow-worm is predominantly a southern-based insect. The glow-worm, Lampyris noctiluca L., is a beetle, related to the bright red soldier beetles (Cantharis spp.) which are so common on flowers such as fool's parsley (Aethusa cynapium L.). Although the male is clearly a beetle, with functional wings and soft elytra that completely cover the abdomen, the female is wingless and remains like the larva. Both male and female are mostly dark brown, but the sides of the thorax and abdomen are lighter. Males are from 10 to 13 mm. long, and the females up to 18 mm. long. The head is hidden from above by the thorax in both sexes. The larva has a softer thorax with biunter hind angles than the adult female. It feeds on snails, first injectmg them with a digestive juice so that the snail's body is more-or-less liquefied. Adult glow-worms eat rarely or not at all. Glow-worms may be luminescent at all stages of their development, even as eggs, but the adult female gives out most light and uses it as a sex signal. Unlike the light from some fungi and light-producing bacteria, the glow-worm's signal is not continuous. A signalling female lifts her abdomen to show the phosphorescent areas on the lower surface of the last three segments. T h e light-producing organs consist of an outer "photogen" layer, and an inner "reflector" layer of cells containing urate crystals, which are covered by a transparent layer of cuticle. Yellowish-green light is produced without heat by a sensitised photochemical reaction. It is an enzyme oxidation, granules of "luciferin" being acted upon by "luciferase". T h e excess energy is given out as light similar to that from other sources but without infra-red or ultra-violet. Glow-worms are mostly found on damp, grassy banks. The previously-mentioned survey includes reports from Sulfolk of glow-worms seen at ClĂ¤re, Sudbury, Bamham Heath, Redgrave Fen, Baylham Heath, Bealings, Campsey Ash, Blaxhall Heath, Westleton Walks, Sizewell, Walberswick, and the DunwichMinsmere area (where they were "quite common during the war"). They are still quite common on the top of the cliffs near Dunwich, and were particularly so in the summer of 1970 (H. G. Burdon), but the general impression of members of the Bury St. Edmunds Naturalists' Society is that they "are not as numerous as they
heath some four years ago, but occasionally saw large numbers in the past. J . T . Death recalls that soon after Dunkirk (1940), when invasion by the Germans was expected, he was one of a L . D . V . group (the defence force that became the " H o m e G u a r d " ) called out to investigate what was thought to be a Sabotage attempt being made on the railway line near Lavenham. T h i s proved to be flashes of light being given out by concentrations of glow-worms on the track and railway banks, closely resembling light from electric torches. For most of us finding glow-worms is not such a worrying experience, and is less frequent than we might wish.
Reference Anon. (1971). The British Naturalists' Association glow-worm survey. Country-side (N.S.) 21, 457-63. Dr. G. D. Heathcote, F.R.E.S., M.Inst.Biol., 2 St. Mary's Bury St. Edmunds, Suffolk.