A broad observation of these interesting creatures
reveals the following :
Glow worms are the larvae of a large
mosquito-like fly that have a very unusual lifestyle.
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Here we have a photo of male
and female flies mating adjacent to a pupal casing from which the female fly has emerged. click image for full frame shot |
Glow worm flies in the
Springbrook area are of the genus Arachnocampa.
Arachnida, Arakhne ~ spider , (L. Gk.)
( literally a grub that uses a web like a spider to catch it's prey ).
Subgenus flava Harrison 1966: 880. Australia (Qld)
.Diptera
Classification: Nematocera Arachnocampa flava
Harrison, 1966. |
Glow worms
elect to inhabit a wide variety of terrain including shady protected places with high
humidity but not necessarily constantly wet, and at Springbrook they can be found in:
- the earth walls of roadside cuttings and tracks
- crevices in rock faces
- creek banks
- under protruding rock ledges behind waterfalls
- under rocks on the ground that have a protruding ledge
- and the root masses of large fallen trees .
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Glow worm web illuminated by
the glow worm.
Night photo by Belinda Janke.click
the image for larger view |
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.
A typical web strand showing the droplets is displayed on the RHS.
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.
Because the web strands are 'weighted' with drops of 'insect glue' the whole web seems to
be perfectly balanced and individual strands pendulate in unison in light breezes without
tangling.
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.
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What makes a glow worm glow ?
Glow worms are oxygen
intolerant.
So they use a very simple but ancient chemical
reaction to burn off their body waste that results in the oxygen being reduced back into
pure water which is then flushed out of the glow worm's body.
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Glow worm tail closeup at
night. photo by Stuart Webber
Click the image for a larger view. |
21-04-2009
Glow worm waste product=Water
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At
last....photographic evidence !!!
This photo by Stuart Webber here at the
Springbrook Research Centre has at last achieved photographic evidence of a process that I
have been seeking for many years, i.e. water being expelled from the glow worm's body as a
waste product.
The water produced accumulates in the mucous
tube in which the glow worm resides until it creates a weak spot into which to drain. The
subsequent 'pendulous bag' bursts and the water falls to the ground.
The lesion created by this action in the tube is sealed over by the excretion of mucous
from the glow worm's body.
Click the image for a larger view. |
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:
| luciferin |
( a waste product of the
organism containing a specific molecule that undergoes a chemical charge when affixed by
an enzyme. ) |
| luciferase |
( the enzyme that acts
upon luciferin ) |
| adenosine triphosphate |
( the energy molecule ) |
| and oxygen. |
|
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 have the ability to very quickly shut down the bioluminescent reaction and
cease glowing in the event of a sudden large disturbance of their webs.
Not really worms ?
The name glow worms is a misnoma as they are larvae, not worms.
Early settlers from the British Isles probably applied the common name 'glow worm' as a
substitute for the English glow worm Lampyris noctiluca, (actually beetle
larvae). As the name 'glow worm' is more aesthetically pleasing than 'glow maggot' or
'glow larvae', this probably accounts for the adoption and retention of the misnoma.
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. The
glow worms that were not crushed by the fallen soil survived and re-located. |
Growth Cycle:
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 site.
Depending on the seasonal conditions at the time of egg-laying, the emergence of larvae
from the eggs can take anywhere from three to six weeks to hatch. On emergence the tiny
larvae immediately start glowing from their tails.
Due to the proximity of eggs laid in each small batch, cannibalism is common if there is a
lack of an alternative food source for the larvae.
Observations of egg numbers from a single fly in the underground controlled environment
performed in 1997 revealed that losses due to natural causes and cannibalism 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.
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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 verify this statement, the last three emergences observed in our
external colonies were:
19-05-2003, 08-10-2003 and 10-02-2004
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 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.
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.

The female pupa is larger and stouter
than the male .
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 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 serves as a miniature controlled environment that both 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 :
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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. |
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Many small and
large varieties of spider co-habit glow worm colonies.
The glow worm's light attracts not only small insects but large ones such as bush
cockroaches and beetles as well that can impact heavily on the unsuspecting glow worm. The
larger spiders, particularly the sentinel and huntsman varieties patrol the walls of the
glow worm colonies without disturbing the glow worms and actually protect the glow worms
from large insect impact by catching the incoming intruders.
So here again we have one of those remarkable symbiotic relationships one finds in nature
wherein the glow worms are attracting large insects as food for the spiders and the
spiders are providing in return a "protection" service to the glow worms.
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.
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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.
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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.
G.Maguire
Photos :
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This photo shows
the glow worm actually spinning a web strand and depositing the sticky globlets on the
thread.
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 ) |
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This photo shows the glow
worm lying in wait for its prey.
(Click the image for a larger view ) |
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Glow worm
(starting to pupate) |

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Glow worm
(Pupal stage)
Note the shortening of the web strands. |
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Glow worm in
final pupal stage.
The web strands due to lack of
maintainence will dry out and disintegrate within 7/10 days leaving only the pupa. |
| Please note:
The above text is published for information
of persons interested in glow worms, and is constantly being updated as we learn more
about these interesting creatures.
The text and photos are made freely available for the use of students doing school
projects provided acknowledgement is made of the source of the material.
Commercial use of any of the above Copyright material without the prior consent of
The Springbrook Glow Worms Research Centre is prohibited.
G.Maguire
References:
Australian Biological Resources Study (NEMATOCERA: Arachnocampa v
flava) |
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