Glow-worms
Glow-worms are New Zealand’s underground stars. Small but bright, it is no wonder why they attract so many tourists to places such as Waitomo and Paparoa National Park.
Living things often have a common name, scientific name and, in New Zealand, a Māori name. Names usually provide information that describes the living thing. Glow-worms are no different. Their Māori name is titiwai, meaning ‘lights reflected in water’, and their scientific name, Arachnocampa luminosa, translates to ‘bright spider-worm’.
Physical description
Glow-worms are not actually worms. They are the larval stage of the fungus gnat, which looks similar to the common mosquito. In their larval state, glow-worms grow from 3–5 mm long when they hatch to a length of 30 mm before they pupate.
Habitat
Glow-worms live in still, dark, damp cave systems and forests where there is appropriate prey. They hang from cave roofs and along stream banks and gully walls. Glow-worms use their mucous glands to create small, flexible tubes – similar to hammocks.
Glow-worm larva in its ‘hammock’
The glow-worm larva is suspended in its hammock-like mucous tube. This glow-worm lives in a bush habitat and its lines are very short – about 20-30 mm in length.
Luring and catching their prey
The prominent feature of the fungus gnat is hinted at in its larval name (glow-worm). This natural glow is called bioluminescence. Glow-worms have a light-producing organ located near their tail, and the glow is a byproduct of excretion. Bioluminescence is created through a reaction of an enzyme called luciferase and a variety of other chemicals.
It is a myth that glow-worms can suddenly switch their lights off when disturbed. They can stop the glow, but it takes several minutes. If they suddenly stop glowing, they have probably moved into a crack or crevice, hiding their light.
New Zealand glow-worm
Glow-worms have luminous tips at the ends of their Malpighian tubules – part of their excretory system – that emit bioluminescent light.
Glow-worms use their mouths to create silk threads and send down droplets of thick mucus to make the lines sticky, enabling them to catch small insects. These ‘fishing lines’ vary in length and number depending on the glow-worm’s habitat. Glow-worms living in caves may have lines up to 500 mm long. Bush-dwelling glow-worms have much shorter lines, making them less likely to become tangled in windy conditions. It takes glow-worms 1–15 minutes to create each line, depending on the length.
Glow-worms use their naturally created light to attract their prey. Mistaking the glow-worms’ light for the open sky, the prey flies upwards and gets caught in the glow-worms’ lines. Glow-worms then emerge from their tube and reach down to eat their prey. However, if the prey is too far down the line to be considered safe, glow-worms will pull up the line to eat the prey. They can also cut oversized or unwanted prey from their lines.
Life cycle
Glow-worms start their lives as eggs, where they spend 10–20 days before hatching to become larvae, which is how they spend most of their life.
Glow-worm life cycle
Glow-worms spend most of their lives in their larval form. This graph shows the average amount of time a glow-worm spends in each life cycle stage over the course of a year.
It’s at this stage of the life cycle where the famous light is produced most brightly, as the new larvae build traps in order to catch their food. Larvae need to consume enough food in this stage, as they do not eat as pupae or adults. Glow-worms stay in this stage for 300–350 days before becoming pupae.
The pupae stage is short, 10–15 days, and is where the larvae undergo metamorphosis. Glow-worms cocoon themselves, similar to butterflies, to form a protective barrier while they prepare for adulthood. Once metamorphosis is complete, glow-worms emerge from their cocoons as adult fungus gnats.
Adulthood is the final stage of the fungus gnat’s life. With only 2–5 days to live, fungus gnats must find partners to breed with before they die. They have no mouth so consume no food as adults, relying only on energy stored in their bodies. After they breed, the females lay clumps of 40–50 eggs and die soon afterwards alongside the males.
Related content
Find out about some of the work being undertaken by New Zealand scientists looking at what makes glow-worms glow and could this lead to some medical breakthroughs?
Nature of science
Life cycle diagrams may reinforce alternative conceptions. Diagrams often depict life stages as beginning with an egg and/or having stages of equal lengths of time. Life cycles are repeated so there is no first or final stage. The length of each stage also varies considerably between different species. Being able to read a graph or diagram fits into the science capability Interpret representations.
Useful links
Scientists used scanning electron microscopy and X-ray spectroscopy to determine what’s in Glow-worms’ sticky droplets. Read about it in this Science Daily article.
Dr Siouxsie Wiles writes about Arachnocampa luminosa in this Sciblogs post.
Dr Miriam Sharpe discusses glow-worms and medical research in this RNZ interview.
Acknowledgement
Christina Schipper produced this article as part of a Queen Scout project.
