Lampyris noctiluca (Linnaeus, 1758)
POLYPHAGA Emery, 1886
ELATEROIDEA Leach, 1815
LAMPYRINAE Latreille, 1817
LAMPYRINI Rafinesque, 1815
Lampyris Geoffroy, 1762
The distribution of the ‘Common glow-worm’ includes almost the entire Palaearctic region from Portugal through Europe and Asia to China, it is also the most northerly member of the family, extending almost to the Arctic Circle, it occurs from lowlands to at least 2000m, at which altitude it occurs in the Swiss alps, and it is locally common throughout most of its range. In the UK it is locally common throughout England and Wales, becoming more scattered and scarce to the far north of Scotland; it is present on Anglesey and some of the inner Western Isles but absent from Man, Orkney and Shetland. Typical habitats include old established grassland, especially in chalk and limestone regions where they occur in open areas or along hedgerows, grass verges, railway embankments, churchyards and parkland etc. Adults are active during June and July although they may extend into August or even September in favourable years, they are short-lived, generally 2 or 3 weeks, and do not feed. Both sexes and all life stages glow but only the adult female conspicuously so. Females are flightless, they hide under stones or in the soil during the day and become active at night when they remain among short grass or low vegetation emitting a yellowish-green glow to attract flying males, they glow from beneath the abdomen and usually remain in one place as they do so, generally with the abdomen curved and moving from side to side, and may glow for a few hours each night for several weeks but as soon as they have mated they stop. Males glow only dimly as they fly low over grass etc. in search of females and it seems they select the strongest glowing females with which to mate, they are very difficult to observe and the best way to find them is to examine females as they glow, occasionally a pair will be found in cop. with the female still glowing. Females begin ovipositing soon after mating and each will lay between 50 and 100 eggs under leaf-litter, among moss or in the soil over a 3 day period, and soon afterwards they die. Eggs are about 1mm in diameter, pale yellow and weakly luminescent. The larvae emerge after 2 or 3 weeks, although they may take much longer in cooler climates, and immediately begin to search for food.
They are distinctive, dark brown with pale spots on the lateral margins of the body segments, and move slowly, pushing themselves along with the abdominal apex, in search of their prey, they are nocturnal and inhabit the same areas as the females although they may occasionally be seen on pathways etc. during the day, and they also glow, less brightly and only intermittently but nonetheless are readily seen on dark moonless nights either on the ground or among low vegetation as they hunt for slugs and snails which seem to be their only prey. They are active between April and October and develop over 2 or 3 years, moulting 4 or 5 times in the process. Winter is passed under matted grass, in tussocks or under stones etc. and we have found them among piled decaying water lily roots and stems beside a grave-pit in South Herts., they will generally be found with the body curved and concertinaed and they remain this way through the winter, becoming active during the first warm days of spring. They are nocturnal and mostly active when the ground is damp, no doubt when their prey is most active, and they may predate molluscs much larger than themselves; they stun the prey with digestive enzymes delivered through a series of bites with their channelled and sharp mandibles but this is not always successful as prey have been seen to escape after being bitten and the defensive slime they produce is generally effective.
Adults and larvae are quite distinctive among our fauna and more especially so if they are found glowing. Males are 10-12mm, fully-winged and have elytra that completely cover the abdomen; they have very large eyes and rather indistinct luminescent organs on the seventh abdominal segment. The rounded and expanded form of the pronotum which generally covers the head is seen only in our other lampyrids but these are otherwise distinct, see here. The female is apterous with distinct luminescent organs on abdominal segments 6-8. When fully-grown the larva measures a little over 20mm, it is variously creamy-white to pink with well-sclerotized dorsal and ventral plates, long legs and paired luminescent organs on the lateral margins of the thoracic and abdominal segments.
Chalk grassland in the chilterns, a typical habitat of glow-worms.