In particular fireflies and glow-worms have been a part of ancient folklore and legend for thousands of years. The early Mayan civilisation associated the firefly with smoking cigars and often adorned their art with firefly images [1]. In Japan the light of a firefly is regarded as a symbol of the souls of the recently deceased, the hitodama.

Bioluminescence even formed the subject of some of the first scientific experiments. In 1672 the English scientist Robert Boyle, during experiments on glow-worms, fungi and bacteria, established some of the basic principles of bioluminescent reactions, it is a cold light; it can be chemically inhibited; and the light reaction is dependent upon air.

BIOLUMINESCENCE IN INSECTS
Luminescent organisms are predominantly found in the oceans and bioluminescent bacteria, jellyfish and deep sea fish are just some of the well know examples of light producing animals in the sea. However, luminescence is evident in many terrestrial organisms such as fungi, worms, millipedes, centipedes and insects.

In insects, bioluminescence is not just restricted to beetles but is also evident in the flies (Diptera). The term glow-worm¹ is used to describe the luminescent larvae of certain fungus gnats that belong to the subfamilies Arachnocampinae, Keroplatinae and Macrocerinae of the dipteran family Keroplatidae. They are found in dark, damp places such as caves, on river banks or near streams and dense forests [2]. Their blue-green emissions assist in the capture of prey, usually small winged insects, which are lured by the light towards snares composed of vertical silk threads coated with sticky mucus droplets. Although the details of the bioluminescent mechanism are not yet established, preliminary investigations show no clear parallels between flies and beetles [3]. But probably the most studied of all bioluminescent insects, however, are the beetles.

Beetles (Coleoptera) constitute the largest taxonomic group of living organisms. This is reflected in the number of luminescent coleopteran species. Over 2000 species are recorded and many more await discovery. Bioluminescent beetles are predominantly found in the beetle superfamily Elateroidea which contains the three main bioluminescent families; Lampyridae (fireflies and glow-worms), Phengodidae (railroad worms) and Elateridae (click beetles). Two other families, Omalisidae and Staphilinidae are also thought to contain bioluminescent taxa. One further family, the Rhagophalmidae, albeit containing well established bioluminescent members, is controversial in its relationship to the other bioluminescent beetle families (see Taxonomy section).

FIREFLIES AND GLOW-WORMS
Fireflies are probably the most well known bioluminescent organism. They are found all over the world and dazzle spectators with either solitary illuminated flight or in their hundreds they can create a Christmas tree light effect by synchronizing their flash patterns.

Fireflies and glow-worms (Lampyridae) emit a green light in the form of pulses and flashes from specialized organs, known as the lantern, which are located in the last abdominal segments and are clearly visibly as pale regions on the beetle’s body. This light emission forms the basis of what has been established for a long time as the sexual communication between adults.

Bioluminescence is also evident in other life stages of luminescent beetles from the egg through to the pupae, although not all species exhibit bioluminescence in all life stages. As far as is known all firefly larvae are bioluminescent but the function of this luminescence is less obvious. A number of theories have been proposed to account for this mechanism the most plausible being defense from predation.

THE BIOLUMINESCENT REACTION
Bioluminescence is predominantly localized in specialized organs of the beetle’s body. In fireflies and glowworms these are mainly found in the last abdominal segments and emit a green light. Bioluminescent click beetles (Elateridae) have three light organs; a pair of dorsal light organs on the pronotum which emit a green light and a ventral organ located on the first abdominal segment which ranges in colour from orange through to green. Even more spectacularly in some railroad worms (Phengodidae) the number of luminous organs increases, with eleven pairs of lanterns emitting green through to orange light located dorso-laterally along the thoracic and abdominal segments. In addition, a luminous organ on the head emitting red is present in some species.

Despite these vast differences in bioluminescence the mechanism for making the light is essentially the same for bioluminescent members in all these three families. Within the cells of the lantern two principle components are found, a substrate luciferin and an enzyme luciferase. Along with ATP, oxygen, and magnesium ions these components provide a unique mechanism for making light found nowhere else in nature. Furthermore, the light emitted is regarded as the most efficient form of light emission characterized to date².

Notes

References

[1] Lopes, L Some Notes on Fireflies. Link
[2] Meyer-Rochow, VB (2007) Glowworms: a review of Arachnocampa spp. and kin. Luminescence 22, 251-265. Link
[3] Viviani VR, Hastings JW, Wilson T (2002) Two bioluminescent diptera: the North American Orfelia fultoni and the Australian Arachnocampa flava. Similar niche, different bioluminescence systems. Photochemistry & Photobiology 75, 22-27. Link
[4] Ando Y, Niwa K, Yamada N, Enomoto T, Irie T, Kubota H, Ohmiya Y & Akiyama H (2008) Firefly bioluminescence quantum yield and colour change by pH-sensitive green emission. Nature Photonics 2, 44-47. Link