| Firefly | |
|---|---|
| Photuris lucicrescens[4] | |
| Lampyris noctiluca mating | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Coleoptera |
| Suborder: | Polyphaga |
| Infraorder: | Elateriformia |
| Superfamily: | Elateroidea |
| Family: | Lampyridae Latreille, 1817 |
| Subfamilies | |
|
Amydetinae[1] Genera incertae sedis:[1] | |
The Lampyridae are a family of insects in the beetle order Coleoptera with more than 2,000 described species. They are soft-bodied beetles that are commonly called fireflies, glowworms, or lightning bugs for their conspicuous use of bioluminescence during twilight to attract mates or prey. Fireflies produce a "cold light", with no infrared or ultraviolet frequencies. This chemically produced light from the lower abdomen may be yellow, green, or pale red, with wavelengths from 510 to 670 nanometers.[5] Some species such as the dimly glowing "blue ghost" of the Eastern U.S. may seem to emit blueish-white light from a distance and in low light conditions, but their glow is bright green when observed up close.[6] Their perceived blue tint may be due to the Purkinje effect.[7]
Fireflies are found in temperate and tropical climates. Many are found in marshes or in wet, wooded areas where their larvae have abundant sources of food. Some species are called "glowworms" in Eurasia and elsewhere. While all known fireflies glow as larvae, only some adults produce light, and the location of the light organ varies among species and between sexes of the same species. The form of the insect that emits light varies from species to species (for example, in the glow worm found in the UK, Lampyris noctiluca, it is the female that is most easily noticed.[8][9]). In the Americas, "glow worms" are the closely related family Phengodidae, while in New Zealand and Australia, a "glow worm" is a luminescent larva of the fungus gnat Arachnocampa.[10]
Fireflies vary widely in their general appearance, with differences in color, shape, size, and features such as antennae. Adults can differ drastically in size depending on the species, with the largest being up to 25 mm (1 in) long. Although the females of some species are similar in appearance to males, many species have larviform females. These females can often be distinguished from the larvae only because the adults have compound eyes; these are much smaller than those of their males and often highly regressed.[11] The most commonly known fireflies are nocturnal, although numerous species are diurnal and usually not luminescent; however, some species that remain in shadowy areas may produce light. Fireflies undergo complete metamorphosis.[12]
A video of fireflies
A few days after mating, a female lays her fertilized eggs on or just below the surface of the ground. The eggs hatch three to four weeks later, and the larvae feed until the end of the summer. The larvae are commonly called glowworms (not to be confused with the distinct beetle family Phengodidae or the fly genus Arachnocampa). Lampyrid larvae have simple eyes. The term glowworm is also used for both adults and larvae of species such as Lampyris noctiluca, the common European glowworm, in which only the nonflying adult females glow brightly and the flying males glow only weakly and intermittently. Fireflies hibernate during the larval stage. Some do this by burrowing underground, while others find places on or under the bark of trees. They emerge in the spring. After several weeks of feeding on other insects, snails, and worms, they pupate for one to two and a half weeks and emerge as adults. The larvae of most species are specialized predators and feed on other larvae, terrestrial snails, and slugs. Some are so specialized that they have grooved mandibles that deliver digestive fluids directly to their prey. Adult diet varies: some are predatory, while others feed on plant pollen or nectar. Some, like the European glow-worm beetle, Lampyris noctiluca, have no mouth.
Most fireflies are distasteful to vertebrate predators, as they contain the steroid pyrones lucibufagins, similar to the cardiotonic bufadienolides found in some poisonous toads.[13]
Photuris in eastern Canada – with flash (top), with only self-emitted light (bottom)
Light production in fireflies is due to the chemical process of bioluminescence. This occurs in specialized light-emitting organs, usually on a female 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.[14] 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.[15][16]
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.[15][17] 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.[18] 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.[15][19] 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.[20] When flash signals are not sufficiently distinguished between species in a population, sexual selection encourages divergence of signaling patterns.[20]
Fireflies in the woods near Nuremberg, Germany, 30-second exposure
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.
Synchronization of flashing occurs in several species; it is explained as phase synchronization and spontaneous order.[21] 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.[22] Congaree National Park in South Carolina is another host to this phenomenon.[23]
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.[15] 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 that males travel upwind along a pheromone plume. Males can find females without the use of visual cues, so sexual communication in P. hemipterus appears to be mediated entirely by pheromones.[24]
The oldest known fossil of the family is Protoluciola from the Late Cretaceous (Cenomanian ~ 99 million years ago) Burmese amber of Myanmar, which belongs to the subfamily Luciolinae. The light producing organ is clearly present.[25] The ancestral glow colour for the last common ancestor of all living fireflies has been inferred to be green, based on genomic analysis.[26]
The family's phylogeny, based on both phylogenetic and morphological evidence by Martin et al. 2019, is:[1]
Fireflies in Georgia, 8-second exposure
Firefly populations are thought to be declining worldwide. While monitoring data for many regions are scarce, a growing number of anecdotal reports, coupled with several published studies from Europe and Asia, suggest that fireflies are in trouble.[27][28][29][30] Recent IUCN Red List assessments for North American fireflies have identified species with heightened extinction risk in the US, with 18 taxa categorized as threatened with extinction.[31][32]
Fireflies face threats including habitat loss and degradation, light pollution, pesticide use, and climate change.[33] Firefly tourism, a quickly growing sector of the travel and tourism industry, has also been identified as a potential threat to fireflies and their habitats when not managed appropriately.[34] Like many other organisms, fireflies are directly affected by land-use change (e.g., loss of habitat area and connectivity), which is identified as the main driver of biodiversity changes in terrestrial ecosystems.[35] Pesticides, including insecticides and herbicides, have also been indicated as a likely cause of firefly decline.[36][37] These chemicals can not only directly harm fireflies, but they also have the potential to reduce prey populations and degrade habitat. Light pollution is an especially concerning threat to fireflies. Since the majority of firefly species utilize bioluminescent courtship signals,[38] they are also very sensitive to environmental levels of light and consequently to light pollution.[38][39] A growing number of studies investigating the effects of artificial light at night on fireflies has shown that light pollution can disrupt fireflies' courtship signals and even interfere with larval dispersal.[40][41][42][43] Researchers agree that protecting and enhancing firefly habitat is necessary to conserve their populations. Recommendations include reducing or limiting artificial light at night, restoring habitats where threatened species occur, and eliminating unnecessary pesticide use, among many others.[37][44][45]
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