The Glow Worm (a/k/a Glow-Worm)

Glow worms (also known as glow-worm or glow worm beetles) are not actually worms at all. Instead they are members of the beetle family. Belonging to the family Phengodidae, the glow worm is often mistaken as a worm, because of their worm-like appearance. Female glow worms, which are the ones that glow, do not develop from larvae into beetle form. Instead, they stay in larva form, although larger than the newly hatched larvae. Male glow worms do develop into beetles, and do not glow.

The glow worm glows because it has special organs (known as photic organs) along its body, paired on each segment. This glow is believed to be a signal to warn predators away, although some researchers suggest it may be a signal to attract male glow worms. The glow makes them easily visible to human eyes at night and that is when they are most active, living in burrows during the day. When they emerge at night, they hunt in leaf litter and sometimes also on tree trunks, although they require a moist environment to survive. They eat millipedes and other small insects.

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Glow worms are native to North and South America. There are also insects in other parts of the world – notably the Unite Kingdom, Australia and New Zealand – that are known as glow worms, but these are from different insect families. Those in the southern hemisphere, for example, are actually types of fly. Glow worms are also sometimes confused with lightning bugs (also known as fireflies). While they are related, lightning bugs belong to the family Lampyridae. They do, however, glow like glow worms.

While glow worms may be fascinating insects, they are best observed in the wild. Whilst it is possible to catch them, it is difficult to keep them alive in captivity. They require a very stable environment. If you are lucky enough to see glow worms, enjoy the spectacle.

Recommended reading (click on the picture for details):
The Glow-Worm and Other Beetles

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