Where is the male’s lantern?

Under abdominal segments 6 and 7

Firefly

Photinus pyralis

The common eastern firefly, or big dipper firefly (Photinus pyralis), is a soft-bodied beetle of North America east of the Rocky Mountains and one of the continent’s most familiar fireflies. On early-summer evenings males flash yellow-green light while swooping upwards in a J shape, and females answer from the grass. Its larvae glow too and live in and under the soil, where they hunt earthworms.

Also known as Common eastern firefly, Big dipper firefly, Eastern firefly

Firefly abilities

J shaped flash path
A searching male flies low, dips, then climbs steeply while he flashes, so his light draws a J in the dusk.
- The dip-and-climb flash is the trademark of this species and gives it the name “big dipper firefly”.
- Scientists collecting fireflies for the 2018 genome study picked out males by their “rising J” flash.
- Other fireflies in the same field draw different shapes and rhythms, which helps females tell species apart.
Sources [2, 3, 10]
≈0.3 s male flash
Each male gives one short flash, about 0.3 s long, and repeats it every 5–10 s while he patrols.
- The 35 described Photinus species in North America each have their own on-off timing of flash length and gap.
- Scientists think nitric oxide gas helps switch the lantern on, by letting oxygen reach the light reaction for a moment. The exact switch is still being studied.
- On a busy evening a field can twinkle with many males flashing at once.
Flash code 6.0 s, repeats
flash 300 ms · dark 5.7 s
Light-talk timing
Male flash≈0.3 s
Female’s wait before answering2–3 s
Gap between a male’s flashes5–10 s
Field averages; timings vary between nights and places.
Sources [3, 10, 11, 12]
2–3 s answer delay
A female perched in the grass twists her abdomen towards a male’s flash and answers with one flash 2–3 s later.
- Her answer, and its timing, is part of the species code, so the male can tell she is a common eastern firefly.
- He flies towards her, and they swap flashes as he homes in.
- Females choose between males, and in Photinus the flash signal matters to that choice.
Sources [3, 4]
41% reactions that make light
Light cells in the lantern mix luciferin, the enzyme luciferase, ATP and oxygen. About 41% of the reacting luciferin molecules give off a particle of light.
- Old books say firefly light is nearly 100% efficient. A 1959 measurement gave 88%, but a careful re-measurement in 2008 found about 41%.
- That is still far more efficient than luminol, a glowing chemical used in labs, at about 0.012, or 1.2%.
- Oxygen reaches the light cells through a dense brush of tiny air tubes.
Light from each reaction (quantum yield)
Firefly, measured 200841%
Firefly, old 1959 figure88%
Luminol (lab glow chemical)1.2%
The share of reacting molecules that give off a photon.
Sources [3, 7, 9, 13]
2 spots larval lightsStill debated
The larva glows from two small spots near its tail end. Its glow rises and falls slowly instead of flashing.
- Scientists think larval glow is mostly a warning to predators that the larva tastes bad.
- A 2024 study found that the bitter lucibufagins evolved after firefly light did, so light may not have started out as a warning.
- The larval lights keep working into the pupa, and for a few days after the adult appears.
Sources [3, 7, 14]
Adults + larvae carry bitter steroids
Common eastern fireflies carry lucibufagins, bitter steroids in their blood that put predators off.
- Lucibufagins were found in large amounts in the blood of adults, and also in larvae.
- In feeding tests, thrushes rejected two other Photinus species, and lucibufagins were at least partly why.
- These chemicals block a vital pump in animal cells. Fireflies have evolved a resistant version of the pump, so they are not poisoned by their own defence.
Sources [3, 15, 16]
Earthworms main larval prey
The larva lives on and under the soil and seems to specialise in eating earthworms.
- Firefly larvae have jaws that carry a toxin to overpower soft-bodied prey such as earthworms, snails and slugs.
- In the lab, scientists raised this species on pieces of earthworm.
- The larvae live underground and are very hard to find in the wild.
Sources [1, 3]
≈30–50 eggs per female
After mating, a female lays about 30–50 eggs over a few days on moss or in moist soil.
- Mated females store sperm, then lay their eggs over a few days.
- In some fireflies even the eggs glow faintly, using a second luciferase gene.
- The larvae that hatch spend most of their lives in the soil.
Sources [3]

Tap a pin on the model or a part below.

1 black spot on a pink shield
- A shield-like plate called the pronotum covers the head from above, so the head is hard to see from on top.
- In this species the shield is pale yellow with a black spot in the middle, ringed with pink or red.
- When the firefly is grabbed, bitter fluid is reported to ooze from the edges of the shield and wing covers.
Sources [1, 2]
2–3 s a female waits, then answers
- Courtship is a conversation by sight: a male flashes, and a female who sees it answers after a delay of 2–3 s.
- Common eastern fireflies are active at twilight, when there is still some light in the sky.
- In flashing fireflies like Photinus, females choose their mates based on the males’ flash signals.
Sources [3, 4, 5]
- Scientists long thought flashing fireflies don’t use smell to find mates.
- A 2025 study of this species found smell-receptor genes in the antennae, and some are more active in one sex than the other.
- That hints that smell may still matter to common eastern fireflies, but what they smell is not yet known.
Sources [6]
Usually none adult meals
- Adult common eastern fireflies are usually thought not to feed at all.
- Even so, both sexes have been seen drinking nectar from common milkweed flowers.
- Most of the energy for the adult’s 2–3 weeks of flying and flashing is stored up while it is a larva.
Sources [2, 3]
- Fireflies are not flies: they are beetles, in the family Lampyridae.
- Like other beetles they have hardened front wings (elytra) that cover the flying wings. In fireflies these covers are soft and somewhat leathery.
- In this species the covers are black or brown with a pale yellow border.
Sources [1, 2, 3]
J shaped flash path
- The thin flight wings fold away under the wing covers when the beetle lands.
- Males patrol by flying low above the ground.
- Each flash is given as the male dips and then climbs, drawing a J of light. That is where the name “big dipper firefly” comes from.
Sources [2, 3]
2 segments of male lantern
- The light organ, or lantern, is on the underside of the abdomen.
- In males it fills the underside of abdominal segments 6 and 7. In females it is a smaller spot on segment 6 only.
- The light is yellow-green. Its exact shade varies between populations, and pigments in the lantern may help tune it.
Sources [3, 7, 8]
41% of reactions make light
- The lantern is packed with light-making cells called photocytes.
- Inside them, the enzyme luciferase uses ATP (the cell’s fuel), magnesium and oxygen to change luciferin, and the reaction gives off light.
- Oxygen is often the limiting ingredient. Tiny air tubes branch into the lantern in a “tracheal brush” to bring it in.
Sources [3, 7, 9]
- Like every insect, a firefly has six legs.
- Females perch on grass and other plants during courtship.
- When a female sees a male’s flash, she twists her abdomen towards it and gives one answering flash.
Sources [3]

Real common eastern fireflies

Photos from Wikimedia Commons. Some of them can repaint the 3D model.

Common eastern firefly resting on a plantPhoto: Melissa McMasters, CC BY 2.0
MaleBig lantern: the whole underside of abdominal segments 6 and 7 lights up. Flies low at dusk, flashing on a rising J.The searcher: flashes about every 5–10 sIn flight, lantern glowing. Photo: Terry Priest, CC BY-SA 4.0
Rock Creek Park, Washington, DCPhoto: Katja Schulz, CC BY 2.0
Rock Creek Park, Washington, DCPhoto: Katja Schulz, CC BY 2.0
Mount Pleasant, Washington, DCPhoto: Katja Schulz, CC BY 2.0
Photographed in Virginia in JunePhoto: Celari817, CC BY 4.0
Common eastern firefly, eastern USAPhoto: Terry Priest, CC BY-SA 3.0
Photuris firefly (look-alike)A different firefly genus, the “femme fatale” fireflies. Females copy the answer flashes of Photinus females to lure the males in.Hunts Photinus males and steals their bitter defence chemicalsA Photuris firefly, Lower Suwannee National Wildlife Refuge, Florida. Photo: Geoff Gallice, CC BY 2.0
Photuris firefly (look-alike)A different firefly genus, the “femme fatale” fireflies. Females copy the answer flashes of Photinus females to lure the males in.Hunts Photinus males and steals their bitter defence chemicalsA Photuris firefly, Great Smoky Mountains National Park. Photo: Kristof Zyskowski & Yulia Bereshpolova, CC BY 2.0

Firefly by the numbers

Measured by scientists in the field and the lab, with comparisons you can picture.

Length: 9–19 mm; reported range for adults⁠[2, 1]
Male flash: ≈0.3 s; each patrol flash⁠[3]
Between flashes: 5–10 s; a patrolling male repeats his flash⁠[3]
Female answer: 2–3 s; delay after the male’s flash⁠[3]
Adult life: 2–3 weeks; as a flying, flashing adult⁠[3]
Larval life: up to 2 years; reportedly, before it pupates⁠[2]
Eggs: ≈30–50; laid on moss or moist soil⁠[3]
Light per reaction: 41%; of reacting luciferin molecules make a photon (2008)⁠[13, 9]; 2008 measurement41 %Old 1959 figure88 %
Firefly species: ≈2,000; worldwide; 35 described Photinus in North America⁠[19, 10]
Genome: 448.8 million; DNA letters mapped to chromosomes (95% of the 2018 assembly)⁠[3]

Firefly myths and facts

Tap Myth or Fact for each claim, then check the answer.

0 of 8 answered

“Fireflies are a kind of fly.”
“Firefly light is almost 100% efficient.”
“Baby fireflies glow too.”
“Some fireflies eat other fireflies.”
“Adult fireflies need to eat a lot.”
“All fireflies flash in sync.”
“Birds find fireflies tasty.”
“Bright garden lights can stop fireflies finding mates.”

How common eastern fireflies talk with light

A firefly courtship is a quick conversation in light. Each species has its own code of flash length, gap and shape.

≈0.3 s
Male flash
A patrolling male gives one short flash, about 0.3 s long.⁠[3]
5–10 s
Gap
He repeats it every 5–10 s while flying low over the grass.⁠[3]
J
Shape
He flashes while dipping and climbing, so the light draws a J.⁠[3, 2]
2–3 s
Female’s delay
A female answers with one flash after 2–3 s. The delay tells the male she is his species.⁠[3]
35
Photinus codes
North America has 35 described Photinus species, each with simple on-off signals of its own.⁠[10]
82%
Sync helps
In the synchronous firefly, females answered 82% of in-step flashes but as few as 3% of out-of-step ones.⁠[20]

Photuris “femme fatale” females can fake the female answer of Photinus fireflies, so answering is not always safe for the males.

Firefly records

Superlatives and record holders, each checked against its source.

More light per reaction than lab glow
41% vs 1.2%
Firefly light reaction
light per reaction, about 34 times luminol’s⁠[9, 13]
A glowing plant from a firefly gene
1986
Common eastern firefly luciferase
tobacco plants carrying its gene made light when given luciferin⁠[21]
Genome pioneer
2018
Common eastern firefly
genome sequenced, with a Japanese firefly and a glowing click beetle⁠[3]
Ancient family
100+ million years
Fireflies
since the two main firefly lineages split⁠[3]
Split-second teamwork
Milliseconds
Synchronous firefly (Photinus carolinus)
males flash in step to within thousandths of a second⁠[20]
Firefly fans
1 million+ a year
Firefly tourism
visitors to firefly sites in at least 12 countries⁠[22]

A common eastern firefly’s life

Most of a firefly’s life is spent underground. The flashing adult lasts only a few weeks.

Early summer
Eggs in the soil
A mated female lays about 30–50 eggs over a few days, on moss or in moist soil.⁠[3]
Hatching
A glowing larva
The wingless larva has two small lights near its tail end that glow softly.⁠[7]
Up to 2 years
Underground hunter
The larva lives on and under the soil and eats mostly earthworms. It may take up to 2 years before it pupates.⁠[3, 2]
Pupa
Two sets of lights
In the pupa the larval lights still glow, and later the new adult lantern starts working alongside them.⁠[7]
Spring–summer
Adult appears
Adults come out in spring and summer and are easiest to see around twilight.⁠[1, 2]
Dusk
Flash and answer
Males patrol with J-shaped flashes; females answer from the grass after 2–3 s.⁠[3]
2–3 weeks
Lights out
Adults live only about 2–3 weeks, mostly on energy stored as larvae.⁠[3]

Common eastern firefly vs synchronous firefly vs Photuris

Three North American fireflies, three very different ways of using light.

Common eastern firefly (Photinus pyralis) vs synchronous firefly (Photinus carolinus) vs Photuris fireflies
	Common eastern firefly	Synchronous firefly	Photuris fireflies
Scientific name⁠[23, 20, 17]	Photinus pyralis	Photinus carolinus	Photuris (a genus of many species)
Famous for⁠[3, 20, 17]	The J-shaped “big dipper” flash	Males flashing in step together	The femme fatale trick
Male flashing⁠[3, 20]	≈0.3 s flash every 5–10 s, on his own rhythm	In sync with other males, to within milliseconds	Varies by species
Most active⁠[5, 24]	Twilight	Night displays in late May–June (Great Smoky Mountains)	After dark (e.g. Photuris versicolor)
Adult females eat other fireflies?⁠[18, 17]	No: it is prey	No: it is prey	Yes: they hunt Photinus males
Bitter lucibufagins⁠[3, 18, 16]	Makes its own	Photinus fireflies make their own	Can’t make them; steals them from prey
IUCN Red List⁠[25]	Least Concern	Least Concern	Varies: Bethany Beach firefly is Critically Endangered

Synchronous firefly flashing is famous in Great Smoky Mountains National Park, where the park runs a lottery for viewing nights to protect the fireflies.

Are common eastern fireflies endangered?

No: this firefly is listed as Least Concern and is still common in lawns and fields. But some North American fireflies are in real trouble, and light pollution affects even common ones.

IUCN Red List

Least Concern (LC)

Widespread east of the Rocky Mountains, in fields, meadows, suburban lawns, woodland edges and even cities.⁠[25, 23, 26, 3, 2]

IUCN Red List, March 2021

Threats

Light pollutionFewer matings
Bright lights at night drown out flashes. In experiments, added lighting reduced courtship and mating success in this species and cut flashing in a night-active firefly by about 70%.⁠[5, 27, 28]
Habitat lossTop 3
Experts surveyed worldwide named habitat loss, light pollution and pesticide use as the most serious threats to fireflies.⁠[19, 29]
Pesticides
Pesticide overuse is one of the main threats linked to recent firefly declines.⁠[19, 29]
Climate changeDrought, sea rise
Drought and rising seas threaten some North American firefly habitats.⁠[26, 29]

What’s helping

Lights off
Turning off, dimming or adjusting outdoor lights reduces their effect on fireflies and other night insects.⁠[27, 5]
Red light only
When watching fireflies, cover your torch with red film, use it only while walking, point it at the ground and switch it off when you arrive.⁠[24]
Watch, don’t collect
Parks limit visitor numbers to protect firefly displays. Enjoy them where they are.⁠[24, 22]
Red List checks132 species
Scientists have assessed 132 North American fireflies. At least 18 (14%) are threatened, and nearly half lack enough data.⁠[26, 30]

Fireflies with their own status

Bethany Beach firefly (Photuris bethaniensis)Critically Endangered
Critically Endangered.⁠[25]
Southwest spring firefly (Bicellonycha wickershamorum)Vulnerable
Vulnerable.⁠[25]
Synchronous firefly (Photinus carolinus)Least Concern
Least Concern, but its famous displays draw so many people that viewing is managed by lottery.⁠[25, 24]

Firefly quiz

Twelve questions. Every answer is somewhere on this page.

Question 1 of 12Score 0

What kind of insect is a firefly?

Firefly field notes

Diet, food web, safety and badges from the Snappit field guide.

Diet & Feeding

Firefly larvae are hunters that eat mostly earthworms. Adults usually don't feed, though some have been seen sipping nectar.

Primary Foods

Earthworms
Foraging Method: Ambush

Age differences: Larvae are predators and eat mostly earthworms. Adults usually don't feed and live on energy stored as larvae.

Ecological connections

Photuris firefliesEaten by
Female Photuris fireflies copy the answer flashes of Photinus females, then catch and eat the males that fly in.
EarthwormsHunts
Firefly larvae live in and under the soil and seem to specialise in eating earthworms.

Safety

Danger 0/5 · No known danger

Fireflies are harmless: they don't sting or bite. Watch them where they are instead of catching them, and keep lights low so they can find each other.

Traits

Collections

Classification

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Lampyridae
Genus: Photinus

Also known as

Common eastern firefly · Big dipper firefly · Eastern firefly · Lightning Bug

Sources for these firefly facts

30 studies and references · checked Oct 16, 2026

Frequently Asked Questions

How to identify Firefly?

Look for hard wing covers meeting in a line down the back, then compare the antennae, body shape, legs and markings. Metallic colors shift a lot with lighting. Beetle Identifier: upload a photo and compare the visible details.

What is Firefly's wingspan?

14-30 mm

How big is Firefly?

9-19 mm

How long does Firefly live?

14-21 days

What does Firefly eat?

Firefly larvae are hunters that eat mostly earthworms. Adults usually don't feed, though some have been seen sipping nectar.

Where is Firefly usually found?

Fields, meadows, lawns and woodland edges, even in towns and cities.

How many legs does Firefly have?

Are fireflies dangerous?

No. Common eastern fireflies have no sting, and adults usually don’t even eat. Their defence is bitter-tasting chemicals in their blood. Watch them rather than catch them, and never put one in your mouth.

Why do fireflies light up?

Mostly to find a mate. Males flash a species-specific code and females answer, so each can recognise their own species. Larvae glow too, probably to warn predators that they taste bad.

How do fireflies make light?

Light cells in the lantern use the enzyme luciferase, with ATP, magnesium and oxygen, to change a molecule called luciferin. About 41% of the reacting molecules give off light, according to a 2008 measurement.

What do fireflies eat?

Common eastern firefly larvae live in the soil and mainly eat earthworms. Adults usually don’t eat, though some have been seen drinking milkweed nectar.

How long do fireflies live?

Adults live only about 2–3 weeks. Most of the life cycle is spent as a larva in the soil, which may take up to 2 years.

Are fireflies disappearing?

Some are. Of 132 North American fireflies assessed for the IUCN Red List, at least 18 are threatened. The common eastern firefly is listed as Least Concern. Habitat loss, light pollution and pesticides are the main threats.

How can I help fireflies in my garden?

Switch off or dim outdoor lights at night, since bright lights cut firefly courtship and mating. Avoid pesticides, and use a red light if you go out to watch them.

Are glowworms and fireflies the same?

Firefly larvae are often called glowworms, and they do glow. The common eastern firefly larva has two small lights near its tail end.