Overview

Brief Summary

Arachnocampa luminosa is found in New Zealand, in both the North and South islands. Its Māori name is titiwai, meaning "projected over water". The Waitomo Caves in the North Island near Pirongia is one well-known habitat, the caves having become a popular tourist attraction. 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. A species of harvestman preys on the A. luminosa eggs, larvae and pupae, and even the adult flies. A fungus also affects A. 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.

  • Baker, C. H. (2008) Distribution and phylogenetic relationships of Australian glow-worms Arachnocampa (Diptera, Keroplatidae) Molecular Phylogenetics and Evolution 48: 506-514
  • Broadley, R. A. (2012) Notes on pupal behaviour, eclosion, mate attraction, copulation and predation of the New Zealand glowworm Arachnocampa luminosa (Skuse) (Diptera: Keroplatidae), at Waitomo. New Zealand Entomologist 35(1): 1-9.
  • Broadley, R.A. and Stringer, I.A.N. (2001) Prey attraction by larvae of the New Zealand glowworm, Arachnocampa luminosa (Diptera: Mycetophilidae). Invertebrate Biology 120 (2): 170-177.
  • Broadley, R. A. and Stringer, I.A.N. (2009) Larval behaviour of the New Zealand glowworm, Arachnocampa luminosa (Diptera: Keroplatidae), in bush and caves. In: V.B. Meyer-Rochow (Ed.), Bioluminescence in Focus - A Collection of Illuminating Essays (pp. 325–355). Research Signpost. Kerala.
  • Meyer-Rochow, V.B. (1990) The New Zealand Glowworm. Waitomo Caves Museum Society.
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Ecology

Habitat

Glow-worms need damp places, where the air is humid and still, to construct their snares. Caves and old mining tunnels are ideal. In the forest glow-worm snares are commonest on moist banks beside a stream or in a ravine.

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Trophic Strategy

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.

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Associations

Predators

Glow-worm predators include the long-legged harvestman, a close relative of spiders. This hunter can move skilfully through the sticky snares in search of glow-worm larvae. There is also some cannibalism in dense glow-worm populations during territorial disputes.

Up to 40% of glow-worm pupae in caves are killed by a white fungus that envelops their body.

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During the early part of June a young friend of mine (Mr. Albert Norris) informed me that he had found pupae of the New Zealand "glow-worm" (Bolitophila luminosa) attached to rocks in the big gully of the Botanical Gardens, Wellington, which, from their shrivelled condition, appeared to have been killed by some parasitic insect. I at once examined one of these pupae, and found that it had been destroyed by a species of Hymenoptera, apparently nearly allied to the Family Ichneumonidae. The pupa of the parasite was imbedded in a quantity of refuse matter in the centre of the unfortunate glow-worm pupa. As is often the case with the Hymenoptera a single specimen only was contained in each host.

On June 21st one of the parasites appeared in the perfect condition. It was apterous, and resembled in the closest possible manner a worker ant ; on a further examination, however, I found that the insect was really referable to the Family Proctotrypidae. On June 23rd another parasite emerged. This specimen was furnished with ample wings, and is consequently the male.

The discovery of this parasite adds another chapter to the already remarkable life-history of the New Zealand luminous Dipteron.

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Life History and Behavior

Behavior

Snares

To catch small flying insects, the glow-worm sets up a snare of sticky silk threads. Flying insects see the glow-worm’s light in the dark and fly towards it, because it resembles moonlight shining through the trees. Instead of finding freedom, they become trapped on the sticky threads. Their struggles alert the glow-worm, which pulls in the thread with its mouth. The prey is then killed and eaten.

Glow-worm lines vary greatly in number and length, depending on the size of the larva and where it is living. Forest-dwelling glow-worms hang lines that are only 1–2 centimetres long, because they could get tangled in a breeze. In the still air of caves, lines can reach up to half a metre.

Each line is made of silk with droplets of sticky mucus – like beads on a string. The larva spends much of its time making and repairing the lines. Because of the flexible nature of its tube, the larva can push its head out to grab a line, ingesting it for re-use later.

A worm can make 15–25 lines a night, and will spend about 15 minutes producing each one. The first droplet of mucus is the biggest, then a short length of silk is added, followed by another droplet, then another length of silk. A large glow-worm that is nearly mature may have as many as 70 lines.

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Light Display

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.

In caves the insects light up at any time of the day or night. Outdoor glow-worms start glowing shortly after dark and usually shine all night. Sometimes when a glow-worm is disturbed its light seems to go off suddenly. This is the larva slithering into a crevice, hiding its light. It actually takes several minutes for the larva to shut off the light.

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Life Cycle

Glow-worms are the larvae of the fungus gnat, whose life cycle has four stages:

  • Eggs are laid by the adult fly. Larvae (maggots) hatch three weeks later.
  • A young larva is only a few millimetres long. Over six to nine months the larva grows steadily until it is about 3–4 centimetres long. It hangs loosely from a damp, sheltered surface, inside a horizontal tube made of very flexible silk and mucus. When mature the larva becomes a pupa.
  • In the pupal or cocoon stage the pupa hangs vertically from a thread for about two weeks until emerging as an adult fly.
  • The adult fly cannot feed and lives only a few days – enough time to mate, and for the female to lay about 100 eggs.
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Evolution and Systematics

Functional Adaptations

Functional adaptation

Light helps capture insects: glow worms
 

Special organs in glow worms help lure insects to their sticky silk threads using bioluminescence.

       
  "Before a short adult life as a gnat, larvae in the genus Arachnocampa  spend months as carnivorous glowworms in caves or sheltered areas using  light as a lurea hungry New Zealand glowworm, Arachnocampa  luminosa, lays a trap. From its nest on a cave ceiling, the  glowworm dangles several dozen 'fishing lines,' each studded with evenly  spaced, sticky droplets of mucus. The worm then churns out  bioluminescence from organs on its posterior, attracting passing  insects. These duped bugs get snagged in the gummy threads, and the  glowworm hauls in its catch." (Hadhazy 2009)

  Learn more about this functional adaptation.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Arachnocampa luminosa

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
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Wikipedia

Arachnocampa luminosa

Arachnocampa luminosa, commonly known as New Zealand Glowworm or simply Glowworm, is a species of fungus gnat endemic to New Zealand. Both the larval stage and the Imago are luminescent. The species is known to dwell in wet caves, grottoes and sheltered, humid places in forests. Its Māori name is titiwai, meaning "projected over water".

The species was first described 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 luminosa in 1924.

Distribution[edit]

Arachnocampa luminosa is found in both the North and the South Island and is generally widespread, although populations are isolated due to the lack of suitable habitat in areas where farming is intense and forests were cut down. The Waitomo Caves in the North Island and the Te Ana-au Caves in the South Island are the best known habitats, both caves having become popular and highly frequented tourist attractions.

Other known populations (North Island):

South Island:

Features[edit]

The species' life cycle starts with an egg, which hatches into a larva and then pupates into an adult fly. It spends most of its life in its larval form. The larval stage lasts about 6 to 12 months, depending on available food. The larva emerges from the egg only about 3 to 5 millimeters long, and through its life grows to about 3 centimeters. 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 several time during its lifespan. At the end of the larva stage it becomes a pupa, hanging down from the roof of the cave on a short, silken threat. The pupa stage lasts about 1 or 2 weeks and it glows intermittently. The male almost 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. Adult New Zealand Glowworms do not feed and live only a few days. Both males and females glow, but not as bright as larvae. The sole purpose of the adults 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 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 40cm 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.

Larvae glow to attract prey into their 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. Prey include midges, mayflies, caddis flies, mosquitos, moths, or even small snails or millipedes. When prey is entangled in a snare, the larva pulls it up by ingesting the snare and starts feeding. cannibalism occurs when population densities are high or when adult flies entangle themselves in snares after hatching.

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. It occurs in modified excretory organs known as Malpighian tubules in the abdomen.[1]

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. A species of harvestmen is known to prey on the New Zealand Glowworm in some caves. A fungus also affects the species; 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 greatest danger to glowworms is from human interference through habitat destruction.

References[edit]

  1. ^ 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.

Further reading[edit]

  • 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
  • Broadley, R. A. (2012) Notes on pupal behaviour, eclosion, mate attraction, copulation and predation of the New Zealand glowworm Arachnocampa luminosa (Skuse) (Diptera: Keroplatidae), at Waitomo. New Zealand Entomologist 35(1): 1-9.
  • Broadley, R. A. and Stringer, I.A.N. (2009) Larval behaviour of the New Zealand glowworm, Arachnocampa luminosa (Diptera: Keroplatidae), in bush and caves. In: V.B. Meyer-Rochow (Ed.), Bioluminescence in Focus - A Collection of Illuminating Essays (pp. 325–355). Research Signpost. Kerala.
  • Broadley, R.A. and Stringer, I.A.N. (2001) Prey attraction by larvae of the New Zealand glowworm, Arachnocampa luminosa (Diptera: Mycetophilidae). Invertebrate Biology 120 (2): 170-177.
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