Glow Worm Caves: As Pretty as the Night Sky

January 20, 2016 | Joanne Kennell

Photo credit: 2il org/Flickr (CC BY 2.0)

These caves formed over 30 million years ago.

New Zealand glow worms (Arachnocampa luminosa) have been a popular tourist attraction since the glow worm grotto at Waitomo Caves was opened to the public in the 1880s.  Today, these caves attract over 400,000 visitors each year.

Glow worms are not actually true worms.  In New Zealand and Australia, glow worms are the larvae (maggots) of a species of fly called a fungus gnat.  Fungus gnats look a little like mosquitos, but rather than feeding on blood, they eat mushrooms and other fungi.  

Glow worms have an organ that is similar to a kidney, however they have the special ability to use this organ to create a blue-green light by a process known as bioluminescence.  The chemical reaction that produces this light requires a lot of oxygen, so an airbag surrounds the kidney-like organ, providing it with the oxygen it needs, as well as acting like a reflector which concentrates the light.

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They use these lights to attract small flying insects that get stuck on their web of sticky threads.  In the caves, glow worms light up at any time of the day or night.  However, outdoor glow worms begin to shine just after dark and usually stay lit up all night.

Amazingly, fungus gnats can glow during their entire life cycle (except as an egg), but the larva has the brightest light.  When these worms are disturbed, it may look like their light has disappeared suddenly, but more than likely they’ve hidden within some sort of crack or crevice.  It actually takes several minutes for their light to shut off.

Geological and volcanic activity created the 300 known caves in the Waitomo region.  These caves, made of limestone (a sedimentary and soluble rock) were formed when the region was still under the ocean about 30 million years ago.

Limestone is made from calcareous remains of marine organisms, such as tiny shell fragments, oyster shells and scallop fossils.  These caves are made of up layers and layers of limestone, compacted under additional layers of sand and mud.  They were lifted up from the ocean by tectonic forces around 5 million years ago and continue to slowly rise today.

If you find yourself at the caves, you will notice several abandoned gorge and cave passages.  This is due to the stream within the caves being diverted several times, when the river found a new path along a new fracture in the limestone.  Luckily for us, this process has left several large passages, partly or completely abandoned by the water — making it possible for us to venture inside and capture images of the dazzling glow worms.

I don’t know about you, but I would love to take a trip to these caves.  And if you do go, make sure you have a camera that is capable of taking high-resolution night time photos — otherwise the pictures may look a little blurry.

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