EOL-media-18-https://www.inaturalist.org/photos/5914483

Cave glow worms (genus Arachnocampa) are found in both New Zealand and Australia. There are at least five species in this genus; the species pictured here is Arachnocampa luminosa and is endemic to New Zealand, occurring on both the north and south islands. Endemic species occur nowhere else on earth except one specific location. New Zealand, having been isolated from any other land mass for over 80 million years (the longest period of isolation of any nonpolar landmass!) has a disproportionate number of endemic species relative to other countries of equal size. This picture comes from Waitomo Caves located in the central north island. Glow worms are not actually worms, but instead are the larvae (maggots) of a fly known as a fungus gnat. These flies spend almost the entirety of their lives (roughly 9 months) as larvae. In fact, the adult stage lasts only only a few days, in which time they mate, and the females lay eggs. But it is the larval stage that is so interesting about this organism as it is bioluminescent. Bioluminescence is the production and emission of light by a living organism. It is a form of chemiluminescence produced by a reaction involving the enzyme luciferase. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some bioluminescent bacteria and terrestrial invertebrates such as fireflies. It is most common in deep-sea organisms, and much less common in terrestrial environments. The glow-worm’s tail-light shines from an organ which is the equivalent of a human kidney. All insects have this organ but the glow-worm has a unique ability to produce a blue-green light from it. The chemical reaction that produces the light consumes a lot of oxygen. An airbag surrounds the light organ, providing it with oxygen and acting as a silvery reflector to concentrate the light. A fungus gnat can glow at all stages of its life cycle (except as an egg), but the larva has the brightest light. Members of this genus are carnivorous, and the worm-like larvae of these species use their glowing lights to attract small flying insects into a snare of sticky threads (pictured here). In the larval form, the glow-worm builds a mucous tube up to 40 centimetres long along the cave ceiling. It then shuttles back and forth along the tube, spewing dozens of long silk threads from its mouth that it leaves dangling from the tube. Each thread is up to half a metre long and a worm can make 15–25 lines a night. These threads are beaded with sticky, mucous-like droplets. A large glow-worm that is nearly mature may have as many as 70 lines. The droplets on the threads trap flying insects attracted to the blue-green light emitted by the tail of the larva. The droplets have been found to be composed of 99 per cent water and 1 per cent glue. The glue was made of urea and glow-worm urine is the most likely source of this urea. Urea is a common waste product in insect urine, and is also used in several industrial glues. Once the insect is stuck, the larva uses its mouth to haul up the fishing line and swallow the prey. Small midges are the usual prey of glow-worms, but all sorts of flying insects get trapped in the sticky snares, including mayflies, caddisflies and moths. Forest glow-worms may also trap spiders, plant hoppers and even millipedes. The glow-worm simply cuts free any prey that is too large, or unwanted. Adult glow-worm flies are never caught in the snares – they are not attracted to the light, and even if they brush against the sticky threads they are strong enough to pull free. Hundreds of Arachnocampa larvae may live side by side on a damp sheltered surface, such as the roof of a cave or an overhanging bank in the forest. Their lights resemble a star-filled night sky. Māori call them titiwai, which refers to lights reflected in water. In caves the insects light up at any time of the day or night. It is a spectacular sight! For more information visit: http://www.teara.govt.nz/en/glow-worms/page-1