Glowing Glowing Gone?
A talk by Dr Tim Gardiner
Glow worms are disappearing fast, but one or two of the audience had seen a few around Waldringfield in recent years. There are more at Dunwich, Westleton, Minesmere and Blacksaw Common.
There is a fungus gnat larve in Waitomo Glow worm Cave in New Zealand which spins silk threads with poisonus mucus that glows. This light attracts prey who think they are heading for daylight.
There are two British glow worms, but the lesser glow worm of Hampshire and Essex is almost extinct.. The male was active in day time and the female only had dots of light. This leaves Lampyris noctiluca as the only one you might be lucky to see.
The glow is a chemical reaction, bioluminescence which is almost 100% efficient in converting energy into cold light.
In this country sightings are getting rare. It is common to count just one, but if you went for a long walk over Dunwich Heath, you might count 100.
The glow worm has a life cycle spanning 3 seasons. It hibernates as a small larva one winter and again the next winter making it susceptible to harsh conditions. The larva live on slugs and snails, needing around 70, so struggle in dry hot summers. They are found on the damp edge of woodland rides and heaths, or railway cuttings.
The larva rides on its prey injecting toxin, gradually liquidising the snail, which it digests over several days.
The eggs and larva flash and glow a little. Possibly a warning that they have a nasty taste. The adult females have a light that glows like an LED when they are ready to mate. The male only glows or makes a flash so is hard to locate. Easier to see the female as she crawls up a grass stem, or sits in full view in a bramble patch, or on a path to be easily seen by the males.
They avoid wet windy nights and don't like the full moon with its competing light. The males can be attracted to bike lights or street lights. Light pollution could be a big problem for them.
Because the female and the larva don't move much it is hard to colonize new sites and inbreeding may be a problem.
The Essex Glow worm survey 2001 started with 8 known locations. Results show huge fluctuations but a steady downward trend over 14 years, especially in hot dry summers.
Habitat management can be a problem. When shrubland or bushes are cleared it helps to leave piles of branches nearby. Sheep graze too heavily but cattle are good. Cutting bays in thickets is good. Railway embankments provide a great environment and a corridor for glow worms to spread along.
If you see any glow worms please report to the national data survey. There is an excellent website
packed with information.