Arachnocampa

Arachnocampa is a genus of four fungus gnat species which are, in their larval stage, glowworms. They are found in New Zealand and Australia in caves and grottos, or sheltered places in forests.

The genus was called Bolitiphila, meaning mushroom lover, in the past. The name was changed in 1924 to Arachnocampa, meaning spider-grub, for the way the larvae hang silk threads to trap prey. The genus Arachnocampa belongs in the family Mycetophilidae.

Common features
Arachnocampa species go through a life cycle of eggs hatching to larvae then pupating to an adult fly. They spend most of their life as larvae.

The larval stage lasts about 6 to 12 months, depending on food. The larva emerges from the egg only about 3 to 5 millimetres long, and through its life grows to about 3 centimeters.

The larva spins a nest out of silk on the ceiling of the cave and then hangs 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. The larvae can only live in a place out of the wind, to stop their lines being tangled, hence caves, overhangs or deep rainforest.

The larva glows to attract prey into its threads. A hungry larva glows brighter than one which has just eaten. Prey include midges, mayflies, caddis flies, mosquitos, moths, or even small snails or millipedes. When prey is caught by a line the larva pulls it up (at up to about 2 millimetres a second) and feeds. If prey is scarce the larvae will turn to cannibalism, eating other larvae, pupae or adult flies.

The glow is the result of a chemical reaction that involves luciferin, a waste product; luciferase, the enzyme that acts upon luciferin; adenosine triphosphate, the energy molecule; and oxygen. It occurs in modified excretory organs known as Malpighian tubules in the abdomen.

The body of the larva is soft while the head capsule is hard. When it outgrows the head capsule it moults, shedding its skin. This happens four times through its life.

At the end of the larva stage it becomes a pupa, hanging down from the roof of the cave. The pupa stage lasts about 1 or 2 weeks and it glows intermittently. The male stops glowing a few days before emerging, the female's glow increases. The glow from the female is believed to be to attract a mate, and males may be waiting there when she emerges.

The adults (of both sexes) cannot feed and live only a short time. They glow, but only intermittently. Their sole purpose is to mate, and for the female to lay eggs. Adult insects are poor fliers and so will often remain in the same area, building a colony of glowworms. The female lays a total of about 130 eggs, in clumps of 40 or 50, and dies soon after laying. The eggs hatch after about 20 days and the cycle repeats.

The larvae are sensitive to light and disturbance and will retreat into their nests and stop glowing if they or their snares are touched. Generally they have few predators. Their greatest danger is from human interference.

Species

 * Arachnocampa luminosa is found in New Zealand, on both the North and South islands. Its  Māori name is titiwai, meaning "projected over water".  The Waitomo Caves on the North Island near Pirongia is one well-known habitat.  It was first known to science in 1871 when collected from a gold mine in the Thames region.  At first it was thought to be related to the European glowworm beetle, but in 1886 a Christchurch teacher showed it was a larvae of a gnat, not a beetle.  The species was called Bolitiphila luminosa in 1891, before renamed Arachnocampa in 1924.  The harvestman spider preys on the luminosa eggs, larvae and pupae, and even the adult flies.  Small orange harvestman spiders live in the same caves as the luminosa, larger spiders will come into the caves for food and shelter.   A fungus also affects the luminosa, it gradually kills the larva.  Fungus spores are spread by air movement, but since the larvae live out of the wind the spread of spores is limited.  The Arachnocampa luminosa species is also found in a small number of places outside New Zealand. In the United States, Dismals Canyon is one such habitat.


 * Arachnocampa richardsae is found in New South Wales. The Newnes Glow Worm Tunnel in the Blue Mountains is one well-known habitat.


 * Arachnocampa tasmaniensis is found in Tasmania (as the name suggests). One habitat is the Marakoopa Cave, Mole Creek near Cradle Mountain.


 * Arachnocampa flava is found in Queensland. The Natural Bridge in the Gold Coast hinterland is one well-known habitat.


 * Arachnocampa Sp.Mt Buffalo. A colony of Arachnocampa has been found in an alpine cave on Mt Buffalo in Victoria. Early research suggests it is a new species, but related to the tasmaniensis and the New Zealand luminosa.  Its presence suggests rainforest may have extended up the mountain in the past.  The Victorian Government presently has it listed (called the Mt Buffalo Glow-Worm) as a threatened species.