Long before humans could light a fire, let alone a light-bulb, nature was already prepared to illuminate the dark! Māori call them titiwai, which refers to the beautiful glim reflected in water. The scientific name, Arachnocampa luminosa, means ” glowing spider-worm,” for the way they hang sticky silk threads to catch small invertebrates that are lured by their mesmerizing glow. They can resemble a night sky full of stars if there are just enough of them – in the bush, along a stream, or even better, in a cave!
Glowworms are carnivorous larvae of fungus gnats. The adults are no bigger than mosquitoes and quite difficult to spot. A hungry larva glows brighter than one which has just eaten. The glow is the result of a chemical reaction that involves luciferin (the substrate), luciferase (the enzyme that acts upon luciferin), adenosine triphosphate (the energy molecule), and oxygen. The reaction occurs in modified excretory organs known as Malpighian tubules in the abdomen.
The larvae hang down as many as 70 threads of silk (called snares) from around the nest, each up to 30 or 40 cm long and holding droplets of mucus (snares built by forest-living specimens are much shorter, reaching a maximum length of 5 cm due to wind entangling longer snares). The larvae are sensitive to light and will retreat into their nests and stop glowing if they or their snares are touched, but they will happily shine even brighter when they sense noise or vibrations. When prey (usually mayfly, stonefly, caddisfly, crane fly or small moth) is entangled in a snare, the larva pulls it up and devours the snare and prey together.
Generally, titiwai have few predators. A species of harvestmen is known to predate upon the New Zealand glowworm. On a rare occasion, you can witness the revenge, when a clumsy harvestmen got tangled in the snares. Glowworms also fall prey to a parasitic fungi. However, the greatest danger to glowworms is from human interference through habitat destruction.
Glowworm cave tours are a largely popular tourist destination in New Zealand (in 2017, at least 500,000 visitors toured Waitomo caves alone). This species is usually found in places of high humidity and where prey populations, such as midges, are also found. Because glowworms are typically found within cave systems, this opens the question of how current and future changes in climatic variability may impact populations.
Check these links for more info on the New Zealand Glowworm in NZ
Wikipedia: Information on the NZ Glowworms
Te Papa Blog: Glowworms
NZ Herald: Tourism
Click on the image to visit the official iNaturalist.nz observation.