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New Zealand Fungus Gnat (NZ Glowworm)

The "glowing spider bug" of New Zealand

Order: Diptera

Family: Keroplatidae (some experts place it in Mycetophilidae)

Genus & Species: Arachnocampa luminosa


Of all the world's creatures, few are as bizarre as the New Zealand fungus gnat. The scientific name Arachnocampa luminosa does a good job in describing this type of fly, as roughly translated it means "glowing spider bug." This is a reference to two of its more peculiar traits: its habit of glowing in the dark, and the method it uses to capture its prey. There are four basic stages within this fly's life: the egg, larvae, pupae, and finally adult (the larvae itself moults four times there are 5 instars).

Adults are rarely seen and so are not well described. They are slightly larger than a mosquito, being just over in (1.5 cm) in length. They have six long legs and, like all flies, have only one pair of wings. Organs known as halteres are located just behind the wings. They act as flight stabilizers, preventing New Zealand fungus gnats from flying upside down. One peculiar feature in the adults is that they lack mouths, and as a result cannot ingest food. Therefore they have short life spans upon emerging from the pupa, males have only 3-5 days to live and females have only 1-2 days. The adults, like the larvae, have the ability to glow, but females often lose their luminescence after laying their eggs.

The larvae are commonly known as glowworms not to be confused with the larvae of fire flies, which are also known as glowworms (fire flies are actually a type of beetle). When the larvae hatch, they are roughly 1/8 in (3-5 mm) in length, but get progressively bigger with each moult, so that by the time they pupate they can be upwards of 1.5 in (3-4 cm) in length, roughly the size of a match. They are voracious hunters and have large mandibles. Their bodies are relatively featureless. The larvae are brown in colour, but the skin is transparent, allowing the bluish-green light to shine through.

All stages of the New Zealand fungus gnat, other than the eggs, glow. This bioluminescence is internal, and is brought about by chemical reactions that occur in a special organ located at the end of the excretory tube. These chemicals include luciferin, which is a waste product that the gnat produces; ATP (adenosine triphosphate), which is a molecule that even we rely on to keep us alive; and oxygen. New Zealand fungus gnats also produce an enzyme known as luciferase. Like all enzymes, luciferase does not react with anything, but rather acts upon one of the chemicals, in this case luciferin, to speed up the reaction. The end result of this reaction is light. This light is used to attract food and mates; the hungrier a larvae is, the brighter it glows. Also, if no male is waiting on a female's pupa when the female is ready to emerge, the female will glow brighter, and will flash its lights on and off. The light turns off when any one of the chemicals needed to produce it is cut off from the light organ. Larvae also produce a brighter light when fighting, but the reason for this is not known.

In total, from egg to adult, New Zealand fungus gnats have a life span of 6-12 months, depending on the availability of food.


New Zealand fungus gnats are common throughout New Zealand, and are often found in damp, sheltered areas such as caves, and are usually associated with streams (in fact, their Maori name, titiwai, means "projected over water"). Although they are quite common, their habitat must meet some requirements: it must be humid, it must have hanging surfaces, it must be dark for a good portion of the day so that their glow can be seen, and the air must be protected from winds, which can tangle up their dangling homes. One of the most famous places for viewing these gnats is Waitomo Cave.

New Zealand fungus gnats are found almost exclusively in New Zealand, but some sources report that they can also be found, in, of all places, Alabama, at a place called Dismals Canyon. While I am not sure if this is true or not, the Dismals Canyon website claims it is.

New Zealand fungus gnats create their own homes from their very own mucous and silk. They can create vast networks of horizontal tubes that they suspend from branches or rock. During the day, they hide in crevices, but when night comes they enter these tubes and begin to hunt. Silk threads that can reach 20 in (50 cm) in length are suspended from these tubes and act as fishing lines. If their habitat is windy, these lines may be less than an inch (2.5 cm) in length.

Larvae are highly territorial. If a larvae enters another larvae's tube, fierce fighting breaks out, and the loser is often eaten.


New Zealand fungus gnat larvae are ingenious hunters. Suspended from their tubes are several dozen "fishing lines" made of silk and covered with globules of sticky mucous. When night comes and the larva begins to glow, various insects that are attracted to the light and fly near get caught in the sticky mucous of the fishing lines. Vibrations are sent up the line and sensed by the larva, which then begins to reel in its catch by swallowing the line. At the same time, certain chemicals within the mucous begins to paralyse the prey so that it doesn't try to break free, or get ensnared in other lines or damage the one its on. When the prey has been reeled up, the larva bites it, kills it, and then either sucks out its juices or eats the entire thing. Since the adults lack mouths, the larvae must eat enough food to keep the adult alive during mating.

New Zealand fungus gnats can be cannibalistic, the larvae often eating other larvae or even adults that happen to fly into the fishing lines. They also catch and feed upon mosquitoes, moths, stone flies, sand flies, caddis flies, midges, ants, spiders, millipedes, and even snails.


The New Zealand fungus gnat has few enemies. Tourists are one of their worst enemies, as they often remove the larvae to get a better look, destroying their homes in the process. Also, if people make too much noise around them, they shut their lights off, and no lights means no food. They do have some natural predators, the first and foremost being other New Zealand fungus gnats. There is also a species of wasp, Betyla fulva, which lays its egg in the pupa. When the egg hatches, the larva eats the occupant inside and then pupates. When the pupa opens, the adult wasp emerges.

New Zealand fungus gnats are quite common and are in no danger of extinction at this present time.


After the adult male emerges from its pupa and dries its wings, it immediately sets out to find a female pupa. When it alights on one, the female within begins to luminesce. This often attracts other males which also land on the pupa, and fights break out as each gnat tries to dislodge the other from the pupa's surface. This ensures that only the strongest males mate with the females. Breeding usually occurs on the mud banks near a stream. Shortly after mating, the male dies, and the female flies off to lay her eggs. She lays the eggs one at a time in clusters of 30-40 and can lay as many as 4 clusters, a total of roughly 130 eggs. This egg-laying can take all day, and afterwards the female dies. The eggs are small and white, but darken to a brown before the larvae emerge. They are coated with a sticky substance and as a result can adhere to whatever they are lain on, whether it be a bank or a crevice. The eggs hatch after 3 weeks, and the larvae emerge.

The larvae hatch with their lights on, and immediately begin to build their homes. The larval stage lasts roughly 6-12 months. When it is time to pupate, the larva arranges its sticky fishing lines into a protective, circular barrier, and then hangs in the middle of this circle. The larva itself begins to shrink and turns opaque as it is encased in the pupal skin. Roughly 12 days after, the adult emerges.


There are three similar species of fungus gnat found in Tasmania, New South Wales, and Queensland, with a possible fourth species being recently discovered in Fiji.