“switched-on bugs” and other glowing critters
I sometimes tell my students that I once sat in front of my aquarium in a dark room reading a book – the light coming from 3 Indonesian flashlight fish. It’s a fact. Some animals (in case of my fish with the help of bacteria) are able to produce surprisingly bright lights. For example, half a dozen peenie-wallies (as the Jamaicans call their large luminescent click beetle) in a plastic bag will allow you to read a letter and Japanese soldiers during the war are said to have crushed tiny and dried luminescent mussel shrimps between the palms of their hands to study maps at night lest enemy spotter planes might see them from above.
All these are examples of bioluminescence, the ability of living organisms to emit light. Nobody exactly knows how and when and why it evolved and to call the phenomenon widespread and rare seems a contradiction. And yet, it’s true, for there is almost no animal phylum with at least one luminescent species and luminescent bacteria and mushrooms are also known. But considering all organisms on Earth, bioluminescence is indeed not very common and, surprisingly, absent in spiders. Animals using bacterial light are actually in the minority. With few exceptions 3 basic ingredients are involved in the production of biological light: a chemical substrate termed “luciferin”, an enzyme called “luciferase” and oxygen. The two terms luciferin and luciferase are non-specific and like the term “sugar” or “vitamin” do not allow a chemist to write down a chemical formula (unless some more information is given on the nature of the compound).
Different luminescent animal species may have different luciferins and luciferases. New Zealand’s large yellow light producing earthworms obtain oxygen for the reaction through breaking down hydrogenperoxide that the worms store in special cells of their bodies. The only light-producing freshwater snail in the world is also a New Zealander. It is black, 5-10 mm long, feeds on algae that it scrapes off submersed rocks and is called Latia neritoides. When attacked it secretes droplets of sticky green-glowing slime, which are followed by the attacker when carried away by the current, leaving little Latia behind unharmed. Other freshwater light emitters include the larvae of several species of fireflies principally in Japan and China.
New Zealand’s famous glowworms (and a first rate tourist attraction in the Waitomo Caves they are), aren’t worms at all, but the glowing larvae of a harmless as an adult short-lived mosquito relative known as Arachnocampa luminosa. The larvae live in caves and other dark places and prey on tiny flying insects which they ensnare with the help of vertical sticky fishing lines of a double strand of very thin silk. To attract its prey the glowworm “burns” bodily wastes and in this way creates a bluish light that tiny flying insects mistake for starlight -a deadly error. A deep sea angler fish has a luminous lantern attached to a fin ray dangling invitingly over its mouth, but krill and other deep water crustaceans are able to emit very brief and powerful flashes of light to temporarily blind the sensitive eyes of some predator and deep sea squid may escape behind a luminescent cloud of glowing “ink”. Deep water fish and squid often form schools and carry luminescent patterns on their bodies. Some luminous fish can adjust the light shining from their undersides to match the dim light from above. This “counter-shading” makes them as invisible to other fish from below as snow hares in the snow became invisible to wolves.
Fireflies send luminous signals to one another and a group of South Asian species has evolved synchronous flashing, which is of course more effective in attracting a female over a distance than one individual’s tiny flash. How synchronicity is achieved by the hundreds of males in one tree is still a mystery. That mainly the rate of flashing rather than the colour of the flashes is important was shown by Dr Ohba in Japan using high-tech artificial firefly dummies. The females were absolutely wrapped and found the electronic males more attractive than the real thing !
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2017.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.