Top facts about glow worms

Jess Price from the Sussex Wildlife Trust gives you the lowdown on glow worms.

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Wherever you are in the UK, one thing is for certain – it has been wet. The continuous rain throughout June and most of July, with only the occasional glimpses of summer, has had an adverse impact on some of our wildlife. Ground-nesting birds have had their nests washed away in floods, bees have struggled to find sunny days for foraging and some butterflies have emerged later in the year than usual. However, one species that may actually benefit from the rain is the glow worm, Lampyris noctiluca.

This is because glow worm larvae feed exclusively on snails and slugs, both of which love dampness. Unfortunately for gardeners, the extraordinarily wet weather has caused a big rise in mollusc numbers. Hopefully this will mean that the number of glow worm larvae making it to adulthood will also increase, but we may not see the effects of this until 2013 or 2014, as it takes two years for glow worm larvae to get big enough to metamorphose into adulthood.

During this time, they are veracious predators turning the slugs and snails they find into a slimy mess. The larvae are armed with hooked jaws that they use to nip at their prey over and over again. Each bite injects a small amount of toxin which slowly starts to dissolve the proteins that make up the slug or snail. This rather gruesome process ends with the glow worm slurping up a snail soup.

In contrast to its grisly larval stage, adult glow worms are benign to the extreme as both males and female lack a mouth. This inability to feed means the clock is ticking from the moment they emerge from their pupa. Adult glow worms have one task only – they need to reproduce and they need to do it quickly.

Despite their name, glow worms are actually beetles rather than worms and it is only the females that glow. She does this to attract a male. Female glow worms have no wings so cannot easily move around to find a mate. Instead they climb up grass stems and switch on their lights. The glowing acts as beacon to the males who have excellent sight and spend their limited time flying around looking for females. Once they have mated, females turn out their lights, use all of the energy they have left to lay 50 to 100 eggs and then die.

Both sexes only live for two or three weeks as adults, so they can’t let a bit of rain get in the way of the need to reproduce.

In the UK, glowing females can be seen from May to September, however the main glow worm season in Sussex is late June/July. They are mostly found on edge habitats of unimproved grassland, as these contain longish grass that the females can climb up and are usually open enough to give the males a good view. Unfortunately these types of habitats are harder to find and those that remain are small and fragmented. Maybe the wet summer and increase in snails will give glow worms the boost they need?

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