Forget about fairies — glow-worms and fireflies are far more fascinating creatures

2014-04-03 00:00

WE got used to seeing glow-worms and fireflies when we first moved to Pietermaritzburg in the mid-seventies, but since moving into a busier suburb some 20 years ago, we have not seen them.

Imagine my excitement when I found a large (about three centimetres long) glow-worm in our garden this summer. Trying to take a photo of it proved far more problematic than I had expected. I wanted to capture the details of its anatomy, while also showing its ability to glow in the dark. I eventually gave up and took two photos — one at night with the animal resting on some printed material, so that its light could be appreciated, and one sitting on a leaf in daylight. I think the photos turned out quite well. Let’s talk about these fascinating creatures.

Glow-worms are the wingless females of fireflies and are actually beetles of the family Lampyridae, and so are neither worms nor flies. There are about 30 southern African species. The winged male firefly usually emits light from its hind end in a series of controlled flashes. The light is produced when a luminous substance, luciferin, is oxidised in the presence of water and an enzyme called luciferase. Although this process takes place internally, the light generated shines out through transparent body segments. This is perhaps the most commonly known example of a phenomenon known as bioluminescence. The function of this bioluminescence is believed to be associated with mate recognition. When ready to mate, a female glow-worm, usually hidden in undergrowth during daylight hours, emits a steady and bright light at night, usually from a prominent perch so that the light can be seen by passing male fireflies. A winged male responds by flashing his light while homing in on the female.

The male specimen depicted here was photographed in the Marloth Nature Reserve near Swellendam as it hung suspended in a spider’s web — making the point that predation is something most insects have to live with. The overall shape of the male’s body is similar to that of the female, except for the possession of wings and large bulbous eyes. Being nocturnal in habit, the males require good sight to pick up the glow produced by the females and hence their well-developed eyesight.

Adult fireflies and glow-worms are relatively short lived as they do not feed. They survive on resources built up in their bodies by the feeding activities of their larvae. Larval lampyrid beetles are predators, feeding mainly on snails. So these insects can be said to be “gardeners’ friends” as they will happily attack and feed on our common garden snails.

In concluding this article, I should tell you that bioluminescence is not restricted to the beetle family Lampyridae but may be found in other families of rather different-looking beetles (such as click beetles), as well as in other major groups of insects (some bugs and gnats), Mollusca (some clams) and Crustacea (some shrimps). Next time you see tiny twinkling lights at the bottom of your garden, dismiss ideas of elves and fairies and go take a look — you may discover something of greater interest.

• Dr Jason Londt is a natural scientist with a special interest in entomology. He welcomes queries and comments, which can be sent to him at

jasonlondt@telkomsa.net

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