Fireflies, glow worms or lighting bugs?
The next time you are relaxing outdoors on a summer evening or even on a game walk, look out for the flashers – fireflies. Also known as glow worms and lightning bugs, these travelling neon billboards of the bush are neither flies, bugs nor worms. They are in fact beetles, belonging to the order Coleoptera, and defined as such by their hardened forewings called elytra, which are not used for flying but rather for balance, while the membranous hindwings do all the work while in the air.
Naturally, the most interesting thing about fireflies is their habit of lighting up the night. How do they do it, and why?
The phenomenon is called bioluminescence and it is used to advertise their presence to possible mates. They can also emit a range of flashes and steady glows, combined with other chemical signals to add pizazz to their campaign and plead their case. Groups of fireflies can synchronise their flashes and particular flash-sequences are peculiar to different species. The predatory female Photuris spp. firefly will mimic the signals of other species in order to attract a meal rather than a mate.
Fireflies emit 'cold light' which has no infrared or ultraviolet frequencies, and may be yellow, green or pale red. The magic takes place in the firefly's light producing organs in the lower abdomen. Here the enzyme luciferase reacts with magnesium ions, ATP and oxygen to act on luciferin, to produce light.
Luciferin, harvested from fireflies, is used in science to test for the presence of ATP and magnesium. It is also thought that the painter Caravaggio prepared his canvases using a powder of dried fireflies to create a photosensitive surface, which he the projected images of his subject onto.
Oddly, the larvae and even the eggs of the firefly also glow, but it is believed that this serves as a warning to predators – fireflies are particularly distasteful and can even be poisonous to some creatures. This is due to the presence of lucibufagins, similar to those found in poisonous toads, in their bodies.
There are about 2 000 different species of firefly worldwide and they come in several varieties – flying and flightless (usually the females only), nocturnal and diurnal. Diurnal species are not usually light-emitting, unless they live in a dark woody environment. Some are predatory, some eat pollen or nectar and some, like the European Glow-worm beetle, Lampyris noctiluca, have no mouth.
Fireflies are the world's most efficient light producers, with none of the light-energy wasted on heat. Sounds like an eco-friendly way to light up our lives.