If you look around a damp and sheltered cave or overhanging bank in the bush at night, there is a chance that you will see small lights twinkling back at you. Each of these blue-green pin points is a glow-worm.
What is a glow-worm?
New Zealand glow-worms are the larvae (maggots) of a species of fly called a fungus gnat.
Like all insects, glow-worms have an organ similar to kidneys. But glow-worms have a special ability to use this organ to create a glowing light. They usually turn the light on just after dark and shine all night long.
There are four stages to a glow-worm’s life cycle: egg, larva, pupa and adult.
- The adult fly lays the eggs.
- Three weeks later, larvae (maggots) hatch. Over six to nine months the larva grows to 3–4 centimetres long. It hangs from a damp, sheltered surface, inside a tube it makes out of silk and mucus.
- When it is fully grown the larva becomes covered in a hard skin known as a pupa or cocoon.
- After two weeks, an adult fly comes out of the pupa. An adult glow-worm fly does not have a mouth and cannot feed. It lives only a few days.
Glow-worms make sticky silk threads which hang like fishing lines. Small flying insects are attracted to the light of a glow-worm, and get caught in the threads. The glow-worm pulls in the thread with its mouth and eats the insect. In the bush the lines are 1–2 centimetres long. In caves, where there is no wind to tangle the threads, the lines may be up to half a metre long. A large glow-worm larva may have as many as 70 lines.
Glow-worms around the world
Australian and New Zealand glow-worms are very similar. But in the northern hemisphere, glow-worms are entirely different insects – they are beetles that fly around at night with their tail-lights flashing, and are also known as fireflies.