Scientifically, fireflies are classified under Lampyridae, a family of insects within the beetle order Coleoptera, or winged beetles. While most fireflies are characterized by their use of bioluminescence to attract mates and communicate with others in their species, not all insects within the firefly family produce light. Some communicate using pheromones, a sort of insect perfume.

There are thousands of firefly species spread across temperate and tropical zones all over the world. In New England alone, you might see twenty or thirty species. But all fireflies are classified under five main subfamilies.

LAMPYRIDINAE (SUBFAMILY)

Photinini

If you live in North America, these are the fireflies you're probably most familiar with. Not all fireflies in this subfamily light up, but those that do are generally divided into many closely related species.

Photinus fireflies tend to be the most common of this group; about half an inch long, these produce yellow-green light. The most common amoung this group is Photinus pyralis, or the common eastern firefly. This is most likely what most people will see in their backyards at night. Below is a picture of Photinus pyralis, the most common firefly species you will see at night.

Photinus carolinus is the synchronous firefly species that produces the beautiful synchorized displays in the Appalachian mountains of the US. They occur in 4 US states with Elkmont, Tennessee having the largest populations. They are 8-12.5mm long, and produce a yellow-green synchronized flash in order to signal to females. These fireflies are found in hardwood forests near creeks or rivers. They can be seen in the third week of May to the third week in June starting at 9:30pm eastern time in the US.

Cratomorphini

Pyractomena fireflies produce a yellow-amber flicker that looks a bit like a spark from a campfire.

Phausis

Phausis reticulata also known as blue ghost fireflies. These tiny fireflies are common throughout the southeastern US and are known as the “blue ghost” because they do not flash but glow with an eerie blue or green light. Females of the blue ghost are pale yellow or white in color and lack wings (right in photo below). Males do have wings and can fly (left in photo below). Since they have not be studied extensively little is still known about them and their habits.

Pleotomini

Pleotomus fireflies are relatively uncommon. Both Pleotomus pallens and Pleotomus nigricans occur in the southwest. Scientists are still discussing whether they should be classified as one species or two distinct species. They are also found in Mexico. Pleotomus davisii is found in Tennessee and Kentucky rarely.

The following is an example of Pleotomus sp. larvae. At this stage the larvae glow periodically throughout the night. They are found after dark crawling along the ground in the leaf litter looking for things to eat. The most common time to find them is after a big rain storm preceding a dry period. These particular larvae were found on the river bottom of the Devil's river in Texas during May 2015.

Lampyrini

Microphotus is a small genus of nocturnal glowworm fireflies occurring throughout the southwestern United States and adjacent parts of Mexico. They are found in discontinuous pinyon-juniper and juniper-oak habitats.

Females have no wings and are larva-like in appearance. Both males and females possess paired photic organs on the terminal abdominal sections. Females emit intermittent glows to attract males. Males, while capable of emitting weak glows or flickers, apparently do not use bioluminescence in sexual communication.

Lamprocerini

Tenaspis belongs to a much larger neotropical fauna of fireflies. There is only one species, Tenaspis angularis (Gorham), in the US. These fireflies are primarily found in the Gulf states of the US. Nothing is known about the larval form of this genus.

PHOTURINAE (SUBFAMILY)

Photurinae

Photuris fireflies are larger—almost an inch long—and produce a darker green light. They're very difficult to distinguish from Photinus from their light alone, even for other fireflies; female Photuris often mimic mating flashes from female Photinus fireflies to attract and eat Photinus males. Because of this, Photuris species are sometimes called “femme fatale” fireflies.

Photuris versicolor is a part of a species complex of 17 named species, with an additional 30 or more yet to be named by Jim Lloyd (L. Faust personal communication). Photuris versicolor occurs from the NE of the US, Texas, Utah, Colorado, California, and into parts of Mexico. They are large fireflies, typically 10-15 mm, with females 15-18 mm. They are early season fireflies occuring in late May to late June. There is a predominant diagonal strip on the shoulder of each wing cover. This is one of the predatory fireflies or agressive mimics of other fireflies flash patterns. Females are predatory while males are not. Females are erratic, highly variable flashers, capable of many types of flashes.

Photuris frontalis is part of a species complex that includes Photuris congener. They are a forest firefly. These are smaller fireflies between 9-11mm. They occur across the southern US into Texas. They have a unique flash pattern that varies based on location, habitat, and temperature. They are recognized as the only synchronous firefly of the North American genus Photuris.

LUCIOLINAE (SUBFAMILY)

Luciolinae

This is the largest subfamily of fireflies, with member species scattered throughout Eurasia, Europe, East Asia, and Australia. The fireflies within this subfamily all produce light—and flash rather than emit a continuous glow. Here are a few genera of note within this group.

Peroptyx. Species within this group are mainly found in tropical Asia. Groups of fireflies will synchronize their flashes until thousands are all flashing to the same rhythm, producing a stunning display.

Luciola. These fireflies are sometimes known as “Japanese fireflies,” although they're also found in Asia and more rarely in southern Europe and Africa. In Japanese traditional culture, they are believed to represent the souls of the dead.

Luciola lusitanica Also known as the Portuguese firefly. Males of this species are the only ones that fly, females do not fly. Females are usually found on the ground or in vegetation, they are also bigger than the males. While males flash, females emit a long or continuous yet unsteady yellow glow from one light organ in it's abdomen. One advantage that non-flying female fireflies have is they are often able to lay more eggs than flying females. More energy that normally would be used for flying can be reserved and put towards laying more eggs. This enables a better chance of survival for more of their offspring.

CYPHONOCERINAE

Cyphonocerinae

Pollaclasis This subfamily of fireflies includes two genera that live in North America and Eurasia. They're notable because scientists believe they are the most primitive species of fireflies in existence. One genus within this group displays very weak light, while the other does not light up at all. The following is male Pollaclasis bifaria, found in Mississippi.

OTOTETRINAE (SUBFAMILY)

Ototetrinae

Scientists haven't decided whether this group should be classified as fireflies; while they share many characteristics of other species, members of the group Ototetrinae don't emit light. They're considered very primitive forms of fireflies, and live primarily in Eurasia and North America.

LAMPYRIS (GENUS)

Lampyris

Sometimes referred to by taxonomists as a “catch-all” subfamily classifying fireflies that don't quite fit into other groups, the species in this genus live generally in more temperate northern regions of the world. The group contains both flashing and continuous-glow fireflies. Some larvae species within this group climb trees to feed on snails and bugs.

Lampyris is a genus of firefly within this subfamily found primarily in Britain, and they thrive in old-growth grasslands in soil with high concentrations of limestone and chalk. Only the males fly; the females are larviform, and only they glow. Females crawl onto blades of grass and low vegetation at dusk and emit a yellow-green continuous light to attract mates. Their vernacular name is “glow worm.”