Plants & Animals - Glowing in the Dark (Bioluminescent)

People often find things that glow in the dark to be mysterious and fascinating. Images of glowing Halloween costumes are common in cartoons. Star shaped stickers can be bought in novelty stores and used to decorate a child's bedroom ceiling to mimic a real starry sky after the night light is extinguished. People make practical use of glow in the dark alarm clocks that tell them what time it is without having to get up to turn on the light. ‘Glowing in the dark’ is also employed by many of the so called ‘lower animals’ and invertebrates as part of their ecology.

Living things which are capable of creating their own light are called 'bioluminescent'. Science has known ever since William Beebe explored the darkness of the deep ocean that many deep sea marine species have glowing spots in strategic places or patterns on their bodies. Terrestrial species with similar abilities continue to be discovered. Many of these are small invertebrates and fungi, usually hidden from view in the dense rainforest vegetation, leaf litter or in the soil. Finding new species during the light of day is difficult enough. Finding a newly discovered species with abilities that can only be seen in the dark can be even more difficult.

In the Wet Tropics rainforests, there are a number of living things which produce their own light. These include fungi, fireflies, glow worms, and some large earthworms. It is likely that there are also snail species here which are bioluminescent since many such land snails have been found in Southeast Asia.

How does a living thing create light?

Presented as simply as possible, bioluminescence occurs when the luciferase enzyme and the chemical luciferin react. A third element needs to be present for this reaction to take place which varies according to the type of animal or fungus. For example, in fireflies and glow worms, ATP is required; for jellyfish, calcium would be needed; and peroxide for earthworms. Oxygen is also sometimes required. Whatever the exact reactants are for each animal or fungus, the end result is the release of energy in the form of light.

Why would a living thing want or need to create light?

The chemical reaction described above and the resultant unstable by-product are often referred to by the experts as 'an excited state'. In some cases, this may be a clue as to why an animal might be bioluminescent but the situation is different for each type of animal that has the ability to glow. For fireflies, the ability to glow is useful for attracting mates. The glow worm has a better chance at a full dinner because it uses its pale green light to draw in a curious, unsuspecting meal.

Why would a living thing want or need to create light?

Living things use bioluminescence for a variety of reasons. Glow worms use their pale green lights to attract an unsuspecting meal to their ‘snares’, made of mucous-coated silk threads hanging from tubes in which the glow worms reside. Fireflies use the ability to glow for attracting mates. See the glow worms and fireflies page for more details.

No one knows why many species use bioluminescence. Why would a fungi use light? What use is light to an earthworm living in the dark soil? See also the mushroom and fungi profiles and the worms page in the Invertebrates section.

There are very few researchers in Australia involved in the study of this fascinating aspect of life in the Living Museum, but perhaps as more species are discovered with this strange ability, more answers for the existence of bioluminescence will come to light!

For those interested in the real 'nitty gritty' on bioluminescence, the book "Bioluminescence in Action" edited by Peter Herring is highly recommended (Academic Press Inc. (London) Ltd, (c) 1978, Library of Congress card number 78-54533, ISBN: O-12-342750-9).

Many thanks to Professor Barrie Jamieson of the University of Queensland Zoology and Entomology Department for taking the time to provide his expert assistance and informative materials.