Glowworms

Adult glowworm fly beside empty pupa case.

New Zealand Glowworm (Arachnocampa luminosa)

NZ glowworms are closely related to Australian glowworms which have very similar appearance and behaviour. New Zealand glowworms are larger and have bigger lights. They seem to also thrive in much larger colonies.

On a Spellbound glowworm tour in New Zealand, you will not only find out more about these fascinating and almost magical little creatures, but you will view them up close in their natural habitat. We will be able to show you all their life cycle stages and explain the adaptations they use to live in a cave.

New Zealand glowworms live all over New Zealand; they’re found in forest settings, often on damp overhanging stream banks and very commonly in caves which seem to give the glowworms the best habitat of all.

The “worm” you see on the ceiling of the Spellbound Glowworm Cave is the larval or maggot stage of a fungus gnat fly. The adult fly looks a little like a mosquito, you may see one in the cave but it is so non-descript you might hardly notice it. Cave life is so good for glowworms they usually complete their entire life cycle within the cave.

Glowworm light is made from a biochemical reaction called bioluminescence which takes place at the terminal end of the renal glands or malphigian tubules of the larval glowworm. Energy to make the light is sourced from an energy rich protein, ATP which is manufactured there. Glowworms produce ‘cold’ light, a pure light with almost no associated heat.

Glowworms can turn off their lights. They may do this when there is too much bright light (from the sun or a torch) or to ‘hide’ if disturbed. Sudden loud noises often make them glow brighter.

Glowworm larva lying in a silk hammock. Sticky silk threads hang from ceiling nearby.

The glowworm larva uses the light at its tail end as an irresistible lure to attract small flying insects lost in the darkness of the cave. Adult females can also produce a light at their tail which may help to attract a mate.

The glowworm makes its home in the cave by attaching a silk hammock to the cave ceiling. To catch food, the glowworm larva builds a network of silk threads that hang down vertically all around, and also within reach of its hammock. As the glowworm extrudes each line from its silk glands, it places droplets of very sticky mucus over the thread line. A lost insect will fly towards the larva’s light lure and into a tangle of sticky silk threads and rarely escapes. The glowworm feels the tug of a struggling insect and reaches out of the hammock to haul up its meal. Insects caught in the glowworm’s lines are held there, stuck in the sticky acid mucus until the glowworm is ready to feed.

The glowworm draws the silk line and the trapped insect upwards and into its mouth, sucks out the juices and spits out the hard parts.

When glowworm larvae hatch from eggs, the first to emerge eat later emerging siblings, this gives them a food supply and enables them to crawl away from the egg cluster to establish their own hammock and feeding lines.

Glowworms are very territorial and can sometimes be seen fighting for space. They may eat one another; sometimes a glowworm is pushed off the ceiling and lands in the stream below.

A mayfly is caught on a silk thread.

Why is life so good in caves? There are a number of reasons for large colonies occurring in some caves. Glowworms thrive in stream caves because flowing water transports emerging aquatic insects into the cave. Once emerged, they fly about the cave and are attracted to the glowworm’s light. In New Zealand aquatic insects emerge most months of the year providing a steady food source for glowworms. A healthy unpolluted stream generates lots of food.

Caves are damp and humid all year round, it’s important for glowworm larvae that they do not dry out.

In a cave it’s always dark, giving glowworms more time with their lights on to catch food and this is also thought to give cave dwelling glowworms an advantage over the ones living in the open.

Glowworms survive best in caves which have very little air movement; breezy conditions will tangle the glowworm’s fishing lines making it too hard to catch food and may dry them out.

The Spellbound glowworm cave has such ideal conditions for glowworms to grow and multiply, we think of it as a glowworm paradise!

Glowworm life cycle

  • Egg stage – 22 days
  • Larval stage – 9 to 12 months (this is when all the feeding occurs)
  • Pupal stage – 12-13 days
  • Fly stage – 2-4 days (glowworm flies cannot feed, they exist simply to mate and produce eggs to begin the next generation).