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A Glow Worm isn’t in fact a worm at all, but is the common name for insect larvae and adult larviform females which glow. Specialised cells in the insects’ abdomen produce this ‘bioluminescence’ which gives off a green/yellow light and generates no heat. Glow Worms are luminous not phosphorescent.
The majority of Glow Worms seen in Britain are fireflies (lampyridae). The wingless adult female is the Glow Worm of literature, especially Lampyris noctiluca found throughout Europe including the British Isles.
In this species the male flies but does not glow. A second species of Glow Worm has been found in a small number of sites in Surrey, Sussex and Hampshire. But the lesser Glow Worm (Phosphaenus hemipterus) is not thought to be native to Britain and it’s possible that it may have been introduced accidentally.
The Lampyridae larvae are believed to glow as a warning signal to predators like toads not to eat them as they're mildly toxic.
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Chris Packham joins Glow Worm expert John Tyler to see the creatures in action:
Wildlife lovers go on the trail of one of Shropshire's smallest stars - the Glow Worm
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The Glow Worm can be found in most parts of Great Britain although it appears to be less common in the north than the south. Glow Worms seem to like a habitat which has a mixture of plants growing to different heights. Rather than cultivated land you are more likely to find Glow Worms in areas with a mixture of shorter vegetation like grass and nettles through to shrubs and bushes. Most people in Britain probably live within an hour of a Glow Worm colony.
The Glow Worm spends most of its two year life cycle as a larva, eating, hibernating and growing. Snails make up the majority of the Glow Worms diet, some of which may be 200 times the insects own weight. Rather gruesomely they paralyse their prey by injecting a poison then sucking them dry. The Glow Worm larva eventually turns into a pupa before emerging as an adult. The adult has no mouth parts and so cannot eat at all, and will only live for perhaps 14 days. It spends this time trying to find a mate.
The female glows to attract males, but after mating lays her eggs and dies. Females often don’t travel more than a yard or two in their entire adult life.
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