Common name: Fungus gnat, glow worm
Scientific name: Arachnocampa luminosa
Māori name: titiwai, pūrātoke
Size: larvae 3-6mm, adults 10-15mm
Habitat: Limestone caves, damp shady forest banks, old mine shafts
The larval stage of this insect is well known to most New Zealanders as being the bioluminescent glow worm that lights up our caves and damp forest banks. Māori call glow worms titiwai, which refers to the light they produce being reflected in the water below.
In the 19th century, early entomologists in New Zealand mistakenly identified the glow worm larvae as a type of beetle, because in the northern hemisphere similarly glowing insects are a type of lampyrid beetle (fire flies). However, the New Zealand glow worms are actually the larval form (maggot) of a type of fly called a fungus gnat. The adult form looks like a mosquito, but lack mouth parts and do not feed at all during their short life span. Instead, adults spend their time searching for mates, although some will end up as food for other glow worm larvae as they get tangled up in the silk threads hanging from cave walls.
Larval glow worms make a tubular nest that they reside in, suspended from the cave wall or forest bank, which is made of mucous and silk. They then make a series of silk threads covered in tiny sticky droplets, which look like a string of sparkling beads hanging from the nest. These threads catch flying midges and other small invertebrates that are attracted to the glowing light. Once they have caught a meal, the larval glow worm hauls the fishing line up to their nest, bites into the prey and starts to eat it. The larval stage of the insect lasts around eight to nine months.
The genus name Arachnocampa refers to the spider-like way in which glow worms catch their prey with the silken fishing lines. The species name, luminosa refers to the bright light that the larval and pupal stages emit. The bioluminescence is a produced by a reaction between oxygen in the air and chemicals in the abdomen of the insect. Glow worms can control how much light they give off by varying the amount of oxygen that is allowed into the area where the light is produced.