Friends

of the Wellington Botanic Garden

 

Wellington, the Capital City of New Zealand


There are glow worms in the Garden which are readily accessible for all to visit and enjoy. It was from specimens found in the Garden that the species was formally described.

There is no need to go many miles to the likes of the Waitomo Caves when there is a great display at your back door. Glow worms are widely distributed in this country, and can be found on damp sheltered banks, caves etc. in many places in New Zealand.


HISTORICAL

Glow Worms have been studied in the Wellington Botanic Garden since the end of the 19th Century. Early entomologists believed the NZ Glow worm was a relative of the European firefly. Interestingly, the European firefly is not a fly, but a beetle. The name game is further confused when it is appreciated the NZ glow worm is not a worm, - but a fly!!

The scientific name of the New Zealand glow worm is Arachnocampa luminosa, a crude translation being 'glowing spider bug'. The reference to spiders is in regard to their 'spider web' snares produced by the larvae.

The Maori have named these insects 'titiwai' meaning 'projected over water', which describes their general habitat along streams. The name 'pura toke' is also used, meaning 'one eyed worm' or 'blind worm' .

The European settlers found the glow worms when they arrived in the country and were immediately fascinated with them. The earliest published reports were of insects found in drives in the Thames Goldfields.

The true nature of these insects was first described by a young 18 year old English man George Vernon Hudson, living in Karori Wellington, only a short distance from the Garden. On arrival in Wellington he commenced studying them, and in 1886 said they were the larva of a two winged fly, a 'fungus gnat'. He had studied them along the Garden's Puketea Stream since arriving to Wellington in 1883. In conjunction with Albert Norris they were able to unravel the life history over the next 10 years. Hudson spent in total some 60 years studying and writing about them and other insects in this country while working for the Post Office.

Glow worm adult fly
(Female)
Original drawing by
George V. Hudson 1890

LIFE HISTORY

The Glow Worm adults live for a short time only; 1-2 days for the female and 3-5 days days for the male. The adults cannot eat, only the larvae being able to ingest food. The adult is slightly larger than the mosquito, about 15 mm long. The 'self adhesive' eggs are laid in clusters of 30-40 on banks and in crevices, each female laying on average 130 whitish eggs which darken with age. They are some 0.75 mm in diameter and hatch in about 3 weeks.

On emerging, the larvae light up immediately, and are the stage of the insect that most people will see. They are about 3-5 mm long, and grow over the next 6 to 9 months to 30 mm long, the length of a match stick. In caves with a more assured food supply they can grow to 40 mm long. The larva is the only stage that feeds on small insects, midges and flies, and even other glow-worms. There are 5 instars; the larvae molts 4 times during this period.

Glow worms in garden
Glow worm habitat lit

Glow worm home on bank



At night it is difficult to appreciate their homes, but with a torch you can see the interesting structures they have built. They form a horizontal suspended tube of silk and mucus from which they suspend their silk fishing lines, with droplets of a sticky mucus to catch small gnats and flies, attracted by the glowing lights. These lines can be up to 50 cm long in protected caves, but in the Gardens are normally some 20 to 50 mm long because of the wind. The lines are coated with globules of sticky mucus which traps any insects that comes into contact with it. It is thought the globules also contain a paralyzing chemical to stop the trapped insect struggling and causing damage to the snare.

The larvae pupate for about 12 days. Both the pupa and adult are able to continue glowing. The pupa is transparent, and is some 12-15 mm long. The female in the pupa can glow very brightly during the last 2-3 days before emerging to attract males. A number of males are often seen on the pupa awaiting the female to emerge, mating of

Glow worm larva
Original drawing by
George V Hudson 1890

ten occurs immediately the female emerges. During this time the male flies around in search of the female, who produces the brightest light to attract them. On emerging from the pupa the adults move around the habitat, but neither are strong flyers, the weighty female carrying her load of eggs can travel short distances only.

The brightness of the lights can vary,. When the insect is hungry it will generally glow more brightly. Females in the pupa can glow very brightly, and also female adults, in both cases to attract mates. Occasionally two larvae will fight over space, and will glow very brightly in an attempt to assert their dominance.

Larvae in particular are terrestrial, and will fight if they believe their space is invaded. Often the looser will be the winners dinner. This territorial display results in the insects being quite evenly distributed in colonies, a feature which is readily apparent when you look at their display of glowing lights.

Glow worm pupa
Original drawing by
George V. Hudson 1890

The three drawings are from G.V. Hudson's
original article on Glow worms published in
The Transactions of the NZ Institute
23:43-49 1890

The light emitted by the insect is bioluminencence, the result of a chemical reaction that involves several components- luciferin a waste product, luciferase an enzyme that acts on luciferin, and ATP (adenosine triphosphate), an energy molecule, and oxygen. These combined form an electronically excited product capable of emitting light.

Bioluminescence of glow worm

LUCIFERIN + LICIFERASE +ATP + OXYGEN

= EXCITED PRODUCT + LICIFERASE

= LIGHT

GENERAL COMMENTS

You will see plenty of larvae. You may see some pupa, especially from April to July, but adults, because they are so small and short lived, are rarely seen unless caught in a snare or spiders web. In caves the greatest number of larvae have been identified from October to February, and this seasonality is likely to exist in the Garden. Glow worm colonies are found over quite extensive areas in the Wellington Botanic Garden. George Hudson noted that the best displays were seen under humid conditions with a light north west wind.


Glow worm trap in the Wellington Botanic Garden

When George Hudson studied the insects in the 1880's, he had to wade up the bed of the Puketea Stream, at the bottom of a steep gully. Subsequent development of the Garden has cut paths into the hills creating banks, many with overhanging areas along which the glow worms have found attractive to live. They are now present in considerable numbers, and can be easily seen from those paths in two main areas within the Garden.

The Glow worm Arachnocampa luminosa is unique to New Zealand, although 3 similar species are found in Australia, in Tasmania, New South Wales and Queensland . There are also reports of another species in Fiji.

If you look for them don't make too much noise, or shine torches on them too much, or they will go out. Please do not touch or remove, as they cannot survive away from their natural habitat.


FOR DETAILS OF GLOW WORM TOURS CLICK HERE

INFORMATION

Information on these fascinating and spectacular insects can be seen on an Australian site http://www.maguires.com/glow_worms/about_worms.htm

There is also a site in New Zealand based on the Waitomo Caves which provides a good description of the life cycle. Click link listed at right sub-index window to open this page


Enjoy a visit to these fascinating insects. But please do not touch and disturb - ensure others can visit and also enjoy.

Updated 30-7-2011
 

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