Firefly

Photuris firefly captured in eastern Canada – the top picture is taken with a flash, the bottom with only the self-emitted light

Fireflies in the woods near Nuremberg, Germany, exposure time 30 seconds

Light production in fireflies is due to a type of chemical reaction called bioluminescence. This process occurs in specialized light-emitting organs, usually on a firefly's lower abdomen. The enzyme luciferase acts on the luciferin, in the presence of magnesium ions, ATP, and oxygen to produce light. Gene coding for these substances has been inserted into many different organisms (see Luciferase – Applications). The genetics of firefly bioluminescence, focusing on luciferase, has been reviewed by John Day.[15] Firefly luciferase is used in forensics, and the enzyme has medical uses – in particular, for detecting the presence of ATP or magnesium. All fireflies glow as larvae. In lampyrid larvae, bioluminescence serves a function that is different from that served in adults. It appears to be a warning signal to predators, since many firefly larvae contain chemicals that are distasteful or toxic.[16][17]

Photic emission in the adult beetle was originally thought to be used for similar warning purposes, but it is now understood that its primary purpose is in mate selection. It has been shown that early larval bioluminescence was adopted in adult fireflies, and was repeatedly gained and lost before becoming fixed and retained as a mechanism of sexual communication in many species.[16][18] Adult lampyrids have a variety of ways to communicate with mates in courtships: steady glows, flashing, and the use of chemical signals unrelated to photic systems.[19] Chemical signals, or pheromones, are the ancestral form of sexual communication; this pre-dates the evolution of flash signaling in the lineage, and is retained today in diurnally-active species.[16][20] Signals, whether photic or chemical, allow fireflies to identify mates of their own species. Flash signaling characteristics include differences in duration, timing, color, and repetition, and vary interspecifically and geographically.[21] When flash signals are not sufficiently distinguished between species in a population, sexual selection encourages divergence of signaling patterns.[21]

Some species, especially lightning bugs of the genera Photinus, Photuris, and Pyractomena, are distinguished by the unique courtship flash patterns emitted by flying males in search of females. In general, females of the genus Photinus do not fly, but do give a flash response to males of their own species.

Firefly female

Fireflies in Georgia, U.S., 8-second exposure

Synchronization of flashing is a phenomenon of several firefly species. This phenomenon is explained as phase synchronization and spontaneous order.[22] Tropical fireflies routinely synchronise their flashes among large groups, particularly in Southeast Asia. At night along river banks in the Malaysian jungles, fireflies synchronize their light emissions precisely. Current hypotheses about the causes of this behavior involve diet, social interaction, and altitude. In the Philippines, thousands of fireflies can be seen all year-round in the town of Donsol (called aninipot or totonbalagon in Bicol). In the United States, one of the most famous sightings of fireflies blinking in unison occurs annually near Elkmont, Tennessee, in the Great Smoky Mountains during the first weeks of June.[23] Congaree National Park in South Carolina is another host to this phenomenon.[24]

Female Photuris fireflies are known for mimicking the photic signaling patterns of other fireflies for the sole purpose of predation; they often prey upon smaller Photinus fireflies.[16] Target males are attracted to what appears to be a suitable mate, and are then eaten. For this reason, Photuris species are sometimes referred to as "femme fatale fireflies".

Many fireflies do not produce light. Usually these species are diurnal, or day-flying, such as those in the genus Ellychnia. A few diurnal fireflies that inhabit primarily shadowy places, such as beneath tall plants or trees, are luminescent. One such genus is Lucidota. Non-bioluminescent fireflies use pheromones to signal mates. This is supported by the fact that some basal groups do not show bioluminescence and use chemical signaling, instead. Phosphaenus hemipterus has photic organs, yet is a diurnal firefly and displays large antennae and small eyes. These traits strongly suggest pheromones are used for sexual selection, while photic organs are used for warning signals. In controlled experiments, males coming from downwind arrived at females first, indicating males travel upwind along a pheromone plume. Males were also found to be able to find females without the use of visual cues, when the sides of test Petri dishes were covered with black tape. This and the facts that females do not light up at night and males are diurnal point to the conclusion that sexual communication in P. hemipterus is based entirely on pheromones.[25]

Cyphonocerus ruficollis, a weakly glowing member of the Cyphonocerinae

Firefly systematics, as with many insects, are in a constant state of flux, as new species continue to be discovered. The five subfamilies listed above are the most commonly accepted ones, though others, such as the Amydetinae and Psilocladinae, have been proposed. This was mainly done in an attempt to revise the Lampyrinae, which bit by bit had become something of a "wastebin taxon" to hold incertae sedis species and genera of fireflies. Other changes have been proposed, such as merging the Ototretinae into the Luciolinae, but the arrangement used here appears to be the most frequently seen and stable layout for the time being. Though most groups appear to be monophyletic, some (e.g., the tribe Photinini) are perhaps better divided.

Two groups of subfamilies seem to exist: one containing many American and some Eurasian species in the Lampyrinae and Photurinae; and one, predominantly Asian, made up from the other subfamilies. While the subfamilies as understood here are, in general, monophyletic, a few genera still need to be moved for the subfamilies to accurately represent the evolutionary relationships among the fireflies.

The Rhagophthalmidae are a glow-worm-like lineage of Elateroidea. They have in the recent past usually been considered a distinct family, but whether this is correct is still disputed. Indeed, they might be the only close relative of the puzzling firefly genus Pterotus, which sometimes is placed in a monotypic subfamily.

The genus Phausis, usually placed in the tribe Photinini of the Lampyrinae, might represent another rather distinct lineage instead.]

The oldest known fossil of the family is Protoluciola from the early Late Cretaceous (Cenomanian) aged Burmese amber of Myanmar.