Glow Worm


A glowworm. The larva is at the upper rim of the picture, a little left of the middle. Note the vertical threads with sticky bulbs, similar to the web of a spider.

Arachnocampa is a genus of nine fungus gnat species which have a bioluminescent larval stage. The species are endemic to Australia and New Zealand. The term Glowworm or sometimes Glow Worm originates from Australian or New Zealand. While normally "glowworm" seems to be used in texts, most locations names use two separate words ("Glow Worm"), sometimes a hyphen is used ("glow-worm"). Even the scientific literature seems to use all three versions of the spelling.

Arachnocampa goes through a life cycle from a 3-5 mm long egg via larvae that pupate and then become a mosquito, which lies eggs. The larvae hatch after about 20 days. The larval stage lasts 6 to 12 months, depending on the food supply, and thus takes up most of the life cycle. The larva produces silk threads like a spider (hence the name Arachnocampa=spider caterpillar). It produces a nest and around it up to 70 silk threads which are about 30 cm to 40 cm long and covered with sticky slime droplets. Some species have poison in the droplets to faster overpower the captured prey. Since the threads easily intermingle, the larvae need windless places.

The bioluminescence of the larvae serves to lure prey into their catch threads. The larvae glow brighter when hungry. Their prey is midges, mayflies, caddisflies, mosquitoes, moths, small snails and millipedes. When the prey sticks to the catch thread, the larva pulls it up with up to 2mm/s and then eats it. The larva has a soft body but a hard head capsule. If the capsule becomes too small, the larva sheds its skin. After four moultings, the larva has reached a size of 3 cm and pupates. The pupa hangs on the ceiling and glows periodically, after 1-2 weeks the mosquito hatches. As females glow more and in contrast to the males do not stop glowing before hatching, it is assumed that the glow should attract the males, so that they already wait for the females when they hatch. The mosquitoes do not take up any food, this stage serves only for mating and laying eggs. The female lays three piles with 40 to 50 eggs and dies afterwards.

Arachnocampa very often live in caves, but they are no cave animals. They only love the cool and humid cave air, and of course, the darkness through which their light can attract victims all day long. Since they are dependent on flying insects, they can only be found in caves in which enough insects get lost and which have large openings. They are common in through caves, natural bridges or river caves. Even artificial cavities are populated by them. They can also be found at rock-walls, under overhangs and in the dense undergrowth.

Traditionally four species were known, but a 2010 paper by Claire H. Baker identified five more species. Exceptional is the Arachnocampa buffaloensis, which has so far only been identified in a single alpine cave on Mount Buffalo in Victoria. It is believed that the rainforest once reached this cave and that the species could not leave the cave after the climate change and the disappearance of the rainforest.

  1. Arachnocampa tropica Baker, 2010: north Queensland
  2. Arachnocampa flava Harrison, 1966: Queensland.
  3. Arachnocampa girraweenensis Baker, 2010: southeast Queensland and northern New South Wales
  4. Arachnocampa richardsae Harrison, 1966: New South Wales.
  5. Arachnocampa buffaloensis Baker, 2010: found in an alpine cave on Mount Buffalo in Victoria.
  6. Arachnocampa gippslandensis Baker, 2010: eastern Victoria.
  7. Arachnocampa otwayensis Baker, 2010: western Victoria.
  8. Arachnocampa tasmaniensis Ferguson, 1925: Tasmania.
  9. Arachnocampa luminosa Skuse, 1891: New Zealand, North and South islands.