Arachnocampa


Arachnocampa

Taxobox
name = "Arachnocampa"



image_caption = "Arachnocampa luminosa" larvae
regnum = Animalia
phylum = Arthropoda
subphylum = Hexapoda
classis = Insecta
subclassis = Pterygota
infraclassis = Neoptera
superordo = Endopterygota|
ordo = Diptera
subordo = Nematocera
infraordo = Bibionomorpha
superfamilia = Sciaroidea
familia = Mycetophilidae
genus = "Arachnocampa"
subdivision_ranks = Species
subdivision =
Various - see text

"Arachnocampa" is a genus of four fungus gnat species which are, in their larval stage, glowworms. They are found mostly 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, perhaps luring them into believing they are outdoors, for the roof of a cave covered with larva can look remarkably like a starry sky at night. A hungry larva glows brighter than one which has just eaten. [ [http://springbrook.info/glow_worms/index.htm Springbrook Glow Worms Research Centre] ] 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.Green, L.B.S. (1979) The fine structure of the light organ of the New Zealand glow-worm Arachnocampa luminosa (Diptera: Mycetophilidae). "Tissue and Cell" 11: 457-465. ]

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.

pecies

* "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 larva of a gnat, not a beetle. The species was called "Bolitiphila luminosa" in 1891, before being 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. "Arachnocampa luminosa" is found only in New Zealand. In the United States, the bioluminescent fly larva found at Dismals Canyon is a distant relative, called "Orfelia fultoni". It doesn't make the hanging silk lines of "Arachnocampa" and produces light from a different part of its body.

* "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. [ [http://www.abc.net.au/science/slab/glowworm/default.htm "The Lure of Glow Worms"] , science feature at the Australian Broadcasting Commission] The Victorian Government presently has it listed (called the Mt Buffalo Glow-Worm) as a threatened species. [ [http://www.dse.vic.gov.au/CA256F310024B628/0/ECBE4FF8F1BE1B5BCA2571460020CC9A/$File/FFG+threatened+list+april+2006.pdf Threatened List April 2006] , at the Victorian Department of Sustainability and Environment]

* "Orfelia fultoni" can be found in the Appalachia area of the United States. A National Natural Landmark, named "Dismals Canyon", is home to this variety of larva.

The larvae of Keroplatidae also evidence blue luminescence and is found in almost all european countries, from Portugal in the southwest to Scandinavia in the Northeast.

References

* "The New Zealand Glowworm" by V.B. Meyer-Rochow, 1990, Published by Waitomo Caves Museum Society. 60 pages (ISBN 0-908683-09) [The book can be obtained from: Waitomo Caves Museum, P.O.Box 12, WAITOMO CAVES, NEW ZEALAND]
* "The Glow-Worm", Ormiston Walker and Judy Kerdel, MacMillan New Zealand, 1990, ISBN 0-7329-0121-9. (A children's book.)
* "Glowworm" article, Encyclopædia Britannica, 15th edition

External links

* [http://soilbugs.massey.ac.nz/insecta.php Soil Bugs - An illustrated guide to the New Zealand invertebrates]
* [http://www.waitomocaves.co.nz/glowworm-caves-boat-ride/361/Glowworm+Lifecycle.aspx The Glowworm Lifecycle]
* [http://www.teara.govt.nz/1966/G/Glow-worm/Glow-worm/en Glowworm article in the "Encyclopaedia of New Zealand 1966"]
* [http://www.geocities.com/orchidsnz/wbgglow.htm Glowworms page]
* [http://www.uq.edu.au/~uqdmerri/Pages/GWglow-worm%20home.html Australian glow-worms]


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