click image for full frame shot

Subgenus flava Harrison 1966: 880. Australia (Qld).

Type species: Arachnocampa flava Harrison, 1966.

The use of webs for feeding:
In order to survive glow worms build elaborate traps consisting of anywhere between 10 to 50 plus vertical hanging threads of silk studded with sticky droplets of mucous to catch small insects such as mosquitoes, midges, fruit-fly, gnats etc. that are attracted by the light produced by the glow worm.
The pendulous web strands are attached to a lattice-work of silk threads across the ceiling of their lair. In turn the threads support the suspended mucous tube in which the glow worm resides and travels, enabling the glow worm to be attracted to the vibration of trapped insects.

Note: Interesting to observe insects caught in these web strands not struggling as violently as those caught in adjacent spider webs, which suggests to me that the mucus droplets on the strands possibly contain some form of 'tranquilizer' and this could be worth investigating.

A typical web showing the droplets is displayed here in a 15 minute time exposure.
The length of the glow worm's web depends on the exposure factor .
If protected from the wind, strands can be as long as 100mm.
Web strands in exposed areas rarely exceed 20mm.

Insect "superglue"
2005 note: A study into insect "glue" is currently being persued by the CSIRO. Unfortunately our sample provided for this study in a sealed glass container dried out in transit before analysis could be carried out and no solvent available was able to dissolve the sample.

Why do Glow Worms glow ?
If one goes back to the Carboniferous period of the earth's development (circa 360 million years ago), it has been suggested that many of the new species of plant and insect life in that period were oxygen intolerant.

With oxygen being toxic to these organisms, the simplest way to rid it from their systems was to chemically reduce it to water. During the process of this chemical reaction (described in the next paragraph below) photon emissions (light) are produced, thus the blue-green glow.

What makes a glow worm glow ?

The blue/green glow of the larvae is the result of a reaction between body products and oxygen in the enlarged tips of the larvae's excretory tubes. The light is the result of a chemical reaction  involving several components:

All these combined make an electronically excited product capable of emitting a blue-green light.
To the average person's sight, up close the light appears more blue than green.
Spectrometer readings show the colour is actually in the green colour spectrum.
more detail

Direct moonlight affects viewing of glow worms in exposed area colonies .
Only the brightest glow worms in exposed colonies are visible on full moon nights.
Immature glow worms cannot generate sufficient bioluminescence to compete with bright moonlight and whilst they are in fact glowing they appear not to be.
Glow worms that have their fill of food can shut down the bioluminescent reaction and cease glowing.

Changing Colonies :

In colonies that are exposed to outside weather conditions , it is not unusual to observe a variety of small spiders sharing areas where the glow worm builds it's web sometimes covering the whole glow worm web area and using the light produced by the glow worm to catch insects. This deprivation of their food source may be a contributing factor to migration as some do of necessity move around finding more favourable locations . Overpopulation of glow worms in the initial hatching areas of necessity causes migration otherwise they tend to eat each other.
Natural erosion of soil areas also causes migration to occur and the patterns of colonies here in the soft earth-bank colonies are constantly changing. The writer has observed a free-fall of glow worms from a height of 8 metres due to erosion in a soft earth bank. A few glow worms that were not crushed by the fallen soil survived and re-located.

The life cycle of a glow worm involves four stages: egg, larva, pupa and adult fly.
Eggs are laid in small batches directly onto the walls of the colony.
Depending on the seasonal conditions at the time of egg-laying, the emergence of larvae from the eggs can take anywhere from three to four weeks to hatch.
On emergence the tiny larvae immediately start glowing from their tails.
Observations of egg numbers from a single fly in the underground controlled environment performed in 1997 revealed that losses due to natural causes and canabalism accounted for 70 out of an initial laying of 120.
It must be conceeded that these losses may not be as high in the natural environment due to a wide ranging variety of small insects and fungi that are potential food sources for the larvae being naturally occurring.
Due to the erratic egg-laying paths taken by flies it is not possible to compare the above losses with those in the wild without creating a false environment that in turn would defeat the purpose of the exercise.

Newly emerged female fly adjacent to the pupal casing from which it has just emerged. click image for full frame shot

Previously published documentation by others suggests that the larvae grow over a period of eleven months until they reach a length of about 25mm .

Note: The writer is not convinced that these publications are correct as at least two and possibly three breeding cycles per year , depending on seasonal factors , have been observed in our outside colonies which suggests that the lifespan is much shorter. This combined with observations of actual cycles of emergence in our controlled environment suggests, that with ideal conditions, a life span of approximately five months.

To support this statement, the last three emergences observed in our external colonies were:
19th May 2003
8th October 2003 and,
10th February 2004.
The end of August traditionally displays the largest emergence of juvenile glow worms even though it is the driest time of the year, and this is supported by the 08-10-2003 emergence.
However 19-05-2003 and 10-02-2004 emergences both coincided with above average rainfall in the preceeding month, and this poses a quandry as to why the emergences occur in opposition to the dry climatic conditions.

When conditions are favourable pupation takes place wherein the larvae exude large quantities of mucous around their bodies that dries out and shrinks in size to form the pupal casing, which is suspended slightly downhill of horizontal.
The pupal stage lasts about 12/16 days. A prominent signal of pupation being a noticable 'shrinking' and shortening of the web-strand lengths due to lack of maintainence (see photos below).

Seasonal triggers a probable factor in pupation :

The start of the main pupal cycle on Springbrook varies but seems to occur around the end of August / September which on average is the driest part of the year.
This phenomenon generally appears to coincide with the forming of the flower buds on the native orchids on Springbrook , suggesting that a change of season may initiate a triggering of pupation.
The female pupa is larger and stouter than the male .
Not all glow worms pupate at the same time again suggesting that false seasonal triggers due to variable weather patterns causing variable hatchings of insect life upon which glow worms depend as their food source may be another factor , and more observation is required.
Note: The ongoing drought in 2003 caused an early pupation in May in the area of the external colony that is normally quite moist. The drier areas remained unaffected.
The writer voluntarily operates the rainfall station at Springbrook for the Bureau of Meteorology and the chart below shows the average rainfall at our glow worm facility.

Life span of adult flies:

Approximately two to three weeks later adult flies emerge to re-commence the cycle.
Male flies tend to live longer than females and can live up to four days.
The flies have no mouth parts or means of feeding, they live only to mate and reproduce by laying eggs .
Near fully-developed female flies in their pupal casing have the ability to send a low-intensity pulsating glowing signal to male flies at the time of their impending emergence. As a consequence of their signalling it is not uncommon to observe male flies adjacent to the pupal casings of female flies waiting for them to emerge.

Confined existance:
The entire life of the glow worm larvae is spent inside a suspended mucous tube with it's head facing the escape route into a crevice or safety haven in the rock or earth wall into which they move at remarkable speed when disturbed.
The mucous tube insulates and prevents the glow worm from dessication.
At night inside the tube it moves back and forth breaking through the tube to repair it's web or to feed on trapped insects.
During the day the glow worm hides inside it's safety haven of a crack or hole behind the web to avoid daylight predators.

Interaction between spiders , other insects and glow worms :

	One of our local "brown rock-hoppers" or "sentinel" spiders ( 75mm legspan ) waiting for large insects to be attracted by the glow worm's light.

Many small and large varieties of spider co-habit glow worm colonies.
It is quite common to observe large huntsman, sentinel, trapdoor and funnel-web spiders living in harmony with glow worms. Many other varieties of smaller spiders also live in conjunction with the glow worms.
It is not uncommon to observe small spider webs along side the glow worm web and on occasion actually spun across the whole glow worm's location.
The larger spiders appear to protect the glow worms from potentially disasterous intrusion by much larger insects, moths and beetles that are attracted by the glow worms bioluminescence .

	Another insect that lives in large numbers in conjunction with glow worms is a type of soft-shelled brown cricket . These crickets are found anywhere glow worms are glowing. 04-05-2002: these crickets have been observed eating the luminous fungi that grows here. They don't seem to attack the glow worms, perhaps they mistake glow worms'  bioluminescence  for luminous fungi.
	These primitive looking thorny crickets with unusually large feelers are also spotted on occasion patrolling the glow worm colonies at night. Click the image for larger view

Disappearing worms:
Extremes of temperature particularly very hot winds in the summer or cold dry strong winds in the winter period have a dramatic influence on glow worm survival. These extreme hot or cold winds can cause the demise of large numbers of glow worms in exposed locations.

Strengthening the gene pool ?
It is fairly obvious that female glow worm flies heavily laden with eggs are not the most agile of flying insects and tend to lay their eggs close to the area from which they have emerged from their pupal casings.
The height of the rock wall in our main colony is approximately 10 metres.
On strong warm windy days however the occasional female fly has been observed being "wind assisted" away from the main colony.How far they can fly due to terrain difficulties has yet to be determined.
We have successfully transplanted glow worm larvae from other colonies some 2KM away into the main colony and watch their development with interest.

Photos :

This photo shows the glow worm actually spinning a web strand and depositing the sticky globlets on the thread. Contrary to popular opinion that suggests the glow worm lowers the thread down from the top. In external colonies where the web strands rarely exceed 30mm in length, the glow worm has the extraordinary capacity to extend itself almost to the length of the unmade thread, starts near the bottom and withdraws upwards spitting the web out including the sticky drops as it retreats. Webs spun in wind-protected environments can be much longer, and these longer webs are made by repeating the above proceedure and adding additional lengths to the original. The web spinning method described above was captured on video 12-04-2001 (Click the image for a larger view )

This photo shows the glow worm lying in wait for its prey. (Click the image for a larger view )