During the summer nights, if you travel along the rural roads, you may detect rows of sparkles. These are fireflies, which during the day remain
hidden amongst the weeds, and at night they turn active.
Despite their names, fireflies are not flies but beetles. Their light is "cold light", with no ultra violet rays, and a wavelength varying from 510 to 670 nanometers, pale yellowish or reddish green in color, with a lighting efficiency of 96%.
What's more important, fireflies produce bioluminescence on their own, not using bacteria, like deep sea animals do (fishes, squids, and shrimps).
There are more than 2000 species of firefly, measuring from 0.5 to 2 cm (0.2 to 0.8 inch) included in Lampyridae family and encountered in temperate and tropical zones around the world. Many species can be found in marshes or in wet, wooded areas where their larvae have more abundant sources of food.
Males can fly, but females are devoid of wings, and signal their position by glowing. In European firefly (photo 1), males glow only very weakly and intermittently.
But if you travel to Malaysia, all year round, you could witness a scene that looks like from a fairy-tale: trees that turn on and turn off intermittently. Indeed, those are firefly clouds (from the genus Pteroptyx) (photo 1) that cover the trees.
The phenomenon of a tree "functioning" at unison may be rare, but it does occur. The researchers discovered that the male firefly emits 12 signals per second, while the female lights on continuous current. When a male approaches a female, his signal changes, turning irregular in order to "personalize" it.
But usually, there are more males attracted to the same female, that's why they can imitate the "serenade" of the favorite male, all at once, like an orchestra after the conductor's signaling.
During the sunset, a firefly on a branch turns on its lantern, and the others respond soon and the whole tree starts blinking.
This phenomenon can be encountered at a much lower scale in other parts of the world, too, like in the mountains of southeastern US or Jamaica (Photinus species).
The females of the American fireflies belonging to the genus Photuris use their flashlight to attract the males of other firefly species in order to …eat them (photo 3)! They mimic the light signals that characterize each species. Spiders consume Photinus fireflies, but not Photuris, as their blood is rich in steroids, distasteful for the spiders.
All firefly larvae glow, but they do it in order to warn predators, as they are usually toxic or distasteful.
Maya people even associated the fireflies with the stars and had a firefly god!
In ancient China, fireflies were sometimes captured in transparent or semi-transparent containers and used as short-term lanterns.
In fact, the light emitted by several large fireflies is enough to enable you read a book!
In Malaya, they can be used as hair adornments.
The enzyme that inflicts bioluminescence, luciferase, is used by forensic investigators to detect blood traces at crime scenes but it is also used to detect the presence of pathogen bacteria in biological liquids, in studies of protein denaturation or studying cell populations in alive animals.
In the Americas, from Canada to Chile, there is another family of bioluminiscent beetle, named Phengodidae.
Both larvae and females look like worms, hence the name "glowworms", but these insects are much larger than real fireflies: till 7 cm (2.8 inch) long (photo 4)!
Males are winged and do not eat, but the larvae and females are carnivorous and possess luminescent organs in every segment of their body, looking like little glowing trains.
The light is produced in the same way like in the firefly: luciferine oxidation in the presence of luciferase.
The light can be red, orange, yellow and green.
The lanterns help larvae to find its prey, millipedes and warn predator, like ants, frogs and spiders they are distasteful.
But in New Zealand a type of firefly that is really … a fly… does exist! This species, Arachnocampa luminosa, inhabits only the caves. The larvae are bioluminescent and populate the caves' ceiling and walls.
Their light is bluish-green. In fact, the larvae weave silky lodges (photo 7) like small tubes from which sticky filaments, 30 to 40 cm (1 to 1.3 ft) long, hang downward. The lights lure the prey animals, emerging from water below (midges, mayflies, caddis flies, mosquitoes, moths, snails, millipedes), which are easily caught by the filaments.
You can imagine the show offered by the ceiling of the cave populated by these fireflies, resembling a sky punctuated by stars (photo 5,6). When the females emerge, they keep glowing for two days, enough time for the male to find them. Males do not glow, their lanterns shut off two days before emerging from pupa.
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