With the fall equinox just behind us, the adult firefly season has come to an end across most of the US and Canada. However, that doesn’t mean you have to say goodbye to fireflies just yet! Fall is an ideal time to look for an entirely different stage of the firefly life cycle—the larvae. This is when firefly larvae shine (quite literally!), and nothing says autumn more than pumpkin spice, fluffy scarves, and the heartwarming glows of baby fireflies on a damp, dark night.
The secret lives of larval fireflies
If you’re not familiar with the larval stage of a firefly, you’re in for a treat (and maybe a shock!). Firefly larvae are the juvenile life stage of a firefly, and they look nothing like the adults. These wingless, ground-dwelling creatures are characterized by segmented bodies covered in armor. Furthermore, they light up (typically from two small spots near the end of their body)! Unlike adult fireflies that use bioluminescence in courtship, larval fireflies are thought to produce light as a warning to predators—basically using it as a signal to let them know that they taste bad, and should look elsewhere for a meal.
What many people don’t realize about fireflies is that the adults live for a very short period of time—typically just a few weeks. The larvae, on the other hand, can live up to one or two years! That’s a long time in the insect world. What are they doing during all this time? Eating, mostly. Firefly larvae are predators with a soft spot for snails, slugs, and worms, although some are also known to feast upon plant matter, berries, and other insects. Upon encountering a juicy meal, larvae use their sharp mandibles to bite and deliver a paralyzing toxin. This enables firefly larvae to go after prey that are much larger than them. Once the other creature is immobilized, the firefly larva emits a digestive enzyme that dissolves the prey and makes it easier for the larvae to slurp it up. Gruesome, right?
While some fireflies are generalist predators, others are very particular about what they eat. For example, Pyractomena fireflies are snail specialists that have evolved very narrow heads that can fit within the openings of snail shells. Imagine minding your own business in the comfort of your shelled home, only to look up and see the mandibles of a hungry firefly coming through your door!
LINK: INaturalist
LINK: CC BY-NC
Tracking larval fireflies
Though easy to overlook, firefly larvae are worth seeking out. They are thought to be active primarily after dark, although sometimes can be seen crawling around on vegetation during the day. At night, they are typically seen creeping through leaf litter, wandering around on damp soil, or climbing up vegetation. Not all species are active on the surface—some are fossorial, meaning they spend most of their lives beneath the ground. Because of this, they can be much more difficult to detect, and your efforts may be best spent on more visible species.
Early to mid-fall is a great time to go looking for larvae since they tend to be more active, the weather is often wetter, and they can be easier to spot in the early evening darkness. Pick a couple warm, damp nights to visit promising firefly locations (think forests, riparian areas, wetlands, places with leaf litter). When you get to the area you want to search, turn off all your lights so they don’t interfere with your night vision. Take a little while to let your eyes adjust to the dark. Then start scanning the ground around you, looking for small, roving spots of light. In many cases, if you see one firefly, you’re likely to see several more! Be patient. If you do need light to change locations, try to limit the amount of time it is on, and use one with a red filter. Let your eyes adjust once more. As much as you can, watch your footing. Firefly larvae can’t fly, and they are susceptible to trampling. You want to be sure you aren’t disturbing their habitat or crushing any individuals. If you do find larvae, crouch down low to observe them up close. They can be unexpectedly fast-moving, but their long-lasting glows can help you track them.
LINK: INaturalist
LINK: CC BY-NC
If you’re curious what species to look for and when, we’ve put together a table on larval body features, with some notes about the microhabitats each genus might be found in and the times of year you might encounter them. Keep in mind there are a lot of unknowns and variability when it comes to firefly larvae, and this list is far from comprehensive. But it should give you a good starting point, especially if you use the Firefly Atlas checklist to see which genera are present in your state.
LINK: Checklist
| Genus | Larval body features | Notes |
| Bicellonycha | Flat, oval-shaped; similar to Photuris. | Only found in Arizona and New Mexico in the US. Lives along damp stream sides. |
| Lucidota | Cigar-shaped, similar to Photinus. Often with three parallel lines running the length of the body. | Seems to be associated with decaying wood. |
| Micronaspis | Each segment has four rear-facing spikes. | Active year-round in intertidal areas and around the high tide line in most of its range in Florida. |
| Microphotus | Elongated, with contrasting dark gray and pink coloration. | Seem to be encountered most frequently in the spring. |
| Photinus | Cigar-shaped. May have three subtle parallel lines running the length of the body. | Unlikely to observe because they live in the soil, but sometimes found while gardening. |
| Photuris | Flat, oval-shaped body, a bit reminiscent of an isopod. | May hunt in small groups. Most detectable in the fall (peaking in September). |
| Pleotomodes | Elongated and mottled. | Crawls on the ground in sandy habitats near ant nests. |
| Pleotomus | Elongated; often grayish with pink edging on the hind edges of the segments. | Active year-round. |
| Pyractomena | Flat and elongated, with the front and rear ends pointed. | Larvae of Pyractomena borealis are often found preparing to pupate on tree trunks in early spring. Other species found in wetlands, leaf litter, or grassy areas. |
| Genus | Larval body features | Notes |
| Bicellonycha | Flat, oval-shaped; similar to Photuris. | Only found in Arizona and New Mexico in the US. Lives along damp stream sides. |
| Lucidota | Cigar-shaped, similar to Photinus. Often with three parallel lines running the length of the body. | Seems to be associated with decaying wood. |
| Micronaspis | Each segment has four rear-facing spikes. | Active year-round in intertidal areas and around the high tide line in most of its range in Florida. |
| Microphotus | Elongated, with contrasting dark gray and pink coloration. | Seem to be encountered most frequently in the spring. |
| Photinus | Cigar-shaped. May have three subtle parallel lines running the length of the body. | Unlikely to observe because they live in the soil, but sometimes found while gardening. |
| Photuris | Flat, oval-shaped body, a bit reminiscent of an isopod. | May hunt in small groups. Most detectable in the fall (peaking in September). |
| Pleotomodes | Elongated and mottled. | Crawls on the ground in sandy habitats near ant nests. |
| Pleotomus | Elongated; often grayish with pink edging on the hind edges of the segments. | Active year-round. |
| Pyractomena | Flat and elongated, with the front and rear ends pointed. | Larvae of Pyractomena borealis are often found preparing to pupate on tree trunks in early spring. Other species found in wetlands, leaf litter, or grassy areas. |
Share what you find
If you do find a larva, congratulations! You are one of a small group of people who have had this opportunity. Even in the age of iNaturalist, firefly larvae remain mysterious and poorly understood. For many species, the larval stage has never been observed or described. Considering how lengthy and important a life stage this is for a firefly, it’s a shame we know relatively little about it.
If you are lucky enough to find larval fireflies, consider taking a few photos, jotting down some notes (air temperature and humidity are especially helpful), and sharing what you observe on the Firefly Atlas! While the Atlas protocols are built around adult sightings, we also accept submissions for larvae, and will do our best to help you identify your species. The reality, though, is that we may only get to genus. Due to a lack of morphological studies, species in most firefly genera cannot be reliably identified based on their larval stages. Even so, your observations are a big help to researchers who are trying to learn more about fireflies—especially where they live, when they are active, and what they are eating. All of these data add up and form the foundation for developing effective conservation strategies for fireflies. After all, how can we conserve a species if we don’t know anything about what it’s doing for most of its life? The more we learn, the better we can ensure that fireflies have what they need to thrive throughout their entire lives.
###
Additional reading
For a deep dive into the world of larval fireflies, check out some of the resources below.
Archangelsky, M., & Branham, M. A. (2001). Description of last instar and pupa of Pyropyga nigricans (Coleoptera: Lampyridae, Photinini) and comparison with larvae of other Photinini genera. The Canadian Entomologist, 133(2), 155–164. https://doi.org/10.4039/Ent133155-2
LINK: Https://doi.org/10.4039/Ent133155-2
Archangelsky, M., & Branham, M. (1998). Description of the preimaginal stages of Pyractomena borealis (Randall, 1838) (Coleoptera: Lampyridae) and notes on its biology. Proceedings of the Entomological Society of Washington, 100, 421–430.
Branham, M. A., & Archangelsky, M. (2000). Description of the last larval instar and pupa of Lucidota atra (G. A. Olivier 1790) (Coleoptera: Lampyridae), with a discussion of abdominal segment homology across life stages. Proceedings of the Entomological Society of Washington, 102(4), 869–877.
Buschman, L. L. (1984). Larval biology and ecology of Photuris Fireflies (Lampyridae: Coleoptera) in Northcentral Florida. Journal of the Kansas Entomological Society, 57(1), 7–16.
Buschman, L. L. (1988). Larval development and its photoperiodic control in the firefly Pyractomena lucifera (Coleoptera: Lampyridae). Annals of the Entomological Society of America, 81(1), 82–90. https://doi.org/10.1093/aesa/81.1.82
LINK: Https://doi.org/10.1093/aesa/81.1.82
Buschman, L. L. (2019). Bioluminescent Behavior of North American Firefly Larvae (Coleoptera:Lampyridae) with a Discussion of Function and Evolution. Insects of Western North America, 11. https://api.mountainscholar.org/server/api/core/bitstreams/30ad7887-1f80-4e82-95b6-7f82ffcea474/content
Faust, L. F. (2017). Fireflies, Glow-worms, and Lightning Bugs: Identification and Natural History of the Fireflies of the Eastern and Central United States and Canada. University of Georgia Press. Athens, GA. 356 pp.
McDermott, F. A. (1954). The larva of Micronaspis floridana Green. The Coleopterists Bulletin, 8(3/4), 59–62.
Riley, W. B., Rosa, S. P., Lima da Silveira, L. F. (2021). A comprehensive review and call for studies on firefly larvae. PeerJ 9:e12121. https://doi.org/10.7717/peerj.12121
LINK: Https://doi.org/10.7717/peerj.12121
Waite, E. S., Keller, O., Tonyai, K. K., Smedley, S. R., & Branham, M. A. (2017). Description of the last larval instar of Ellychnia corrusca (Linnaeus, 1767) (Coleoptera: Lampyridae). Annual Meeting of the Entomological Society of America, Denver, CO.
Wenzel, H. W. (1896). Notes on Lampyridae, with the description of a female and larva. Entomological News, 7, 294–296.
Notice: Below is a list of 9 important links included on this page.
1. INaturalist
2. CC BY-NC
3. INaturalist
4. CC BY-NC
5. Checklist
6. Https://doi.org/10.4039/Ent133155-2
7. Https://doi.org/10.1093/aesa/81.1.82
9. Https://doi.org/10.7717/peerj.12121
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With the fall equinox just behind us, the adult firefly season has come to an end across most of the US and Canada. However, that doesn’t mean you have to say goodbye to fireflies just yet! Fall is an ideal time to look for an entirely different stage of the firefly life cycle—the larvae. This is when firefly larvae shine (quite literally!), and nothing says autumn more than pumpkin spice, fluffy scarves, and the heartwarming glows of baby fireflies on a damp, dark night.
The secret lives of larval fireflies
If you’re not familiar with the larval stage of a firefly, you’re in for a treat (and maybe a shock!). Firefly larvae are the juvenile life stage of a firefly, and they look nothing like the adults. These wingless, ground-dwelling creatures are characterized by segmented bodies covered in armor. Furthermore, they light up (typically from two small spots near the end of their body)! Unlike adult fireflies that use bioluminescence in courtship, larval fireflies are thought to produce light as a warning to predators—basically using it as a signal to let them know that they taste bad, and should look elsewhere for a meal.
What many people don’t realize about fireflies is that the adults live for a very short period of time—typically just a few weeks. The larvae, on the other hand, can live up to one or two years! That’s a long time in the insect world. What are they doing during all this time? Eating, mostly. Firefly larvae are predators with a soft spot for snails, slugs, and worms, although some are also known to feast upon plant matter, berries, and other insects. Upon encountering a juicy meal, larvae use their sharp mandibles to bite and deliver a paralyzing toxin. This enables firefly larvae to go after prey that are much larger than them. Once the other creature is immobilized, the firefly larva emits a digestive enzyme that dissolves the prey and makes it easier for the larvae to slurp it up. Gruesome, right?
While some fireflies are generalist predators, others are very particular about what they eat. For example, Pyractomena fireflies are snail specialists that have evolved very narrow heads that can fit within the openings of snail shells. Imagine minding your own business in the comfort of your shelled home, only to look up and see the mandibles of a hungry firefly coming through your door!
Tracking larval fireflies
Though easy to overlook, firefly larvae are worth seeking out. They are thought to be active primarily after dark, although sometimes can be seen crawling around on vegetation during the day. At night, they are typically seen creeping through leaf litter, wandering around on damp soil, or climbing up vegetation. Not all species are active on the surface—some are fossorial, meaning they spend most of their lives beneath the ground. Because of this, they can be much more difficult to detect, and your efforts may be best spent on more visible species.
Early to mid-fall is a great time to go looking for larvae since they tend to be more active, the weather is often wetter, and they can be easier to spot in the early evening darkness. Pick a couple warm, damp nights to visit promising firefly locations (think forests, riparian areas, wetlands, places with leaf litter). When you get to the area you want to search, turn off all your lights so they don’t interfere with your night vision. Take a little while to let your eyes adjust to the dark. Then start scanning the ground around you, looking for small, roving spots of light. In many cases, if you see one firefly, you’re likely to see several more! Be patient. If you do need light to change locations, try to limit the amount of time it is on, and use one with a red filter. Let your eyes adjust once more. As much as you can, watch your footing. Firefly larvae can’t fly, and they are susceptible to trampling. You want to be sure you aren’t disturbing their habitat or crushing any individuals. If you do find larvae, crouch down low to observe them up close. They can be unexpectedly fast-moving, but their long-lasting glows can help you track them.
If you’re curious what species to look for and when, we’ve put together a table on larval body features, with some notes about the microhabitats each genus might be found in and the times of year you might encounter them. Keep in mind there are a lot of unknowns and variability when it comes to firefly larvae, and this list is far from comprehensive. But it should give you a good starting point, especially if you use the Firefly Atlas checklist to see which genera are present in your state.
| Genus | Larval body features | Notes |
| Bicellonycha | Flat, oval-shaped; similar to Photuris. | Only found in Arizona and New Mexico in the US. Lives along damp stream sides. |
| Lucidota | Cigar-shaped, similar to Photinus. Often with three parallel lines running the length of the body. | Seems to be associated with decaying wood. |
| Micronaspis | Each segment has four rear-facing spikes. | Active year-round in intertidal areas and around the high tide line in most of its range in Florida. |
| Microphotus | Elongated, with contrasting dark gray and pink coloration. | Seem to be encountered most frequently in the spring. |
| Photinus | Cigar-shaped. May have three subtle parallel lines running the length of the body. | Unlikely to observe because they live in the soil, but sometimes found while gardening. |
| Photuris | Flat, oval-shaped body, a bit reminiscent of an isopod. | May hunt in small groups. Most detectable in the fall (peaking in September). |
| Pleotomodes | Elongated and mottled. | Crawls on the ground in sandy habitats near ant nests. |
| Pleotomus | Elongated; often grayish with pink edging on the hind edges of the segments. | Active year-round. |
| Pyractomena | Flat and elongated, with the front and rear ends pointed. | Larvae of Pyractomena borealis are often found preparing to pupate on tree trunks in early spring. Other species found in wetlands, leaf litter, or grassy areas. |
Share what you find
If you do find a larva, congratulations! You are one of a small group of people who have had this opportunity. Even in the age of iNaturalist, firefly larvae remain mysterious and poorly understood. For many species, the larval stage has never been observed or described. Considering how lengthy and important a life stage this is for a firefly, it’s a shame we know relatively little about it.
If you are lucky enough to find larval fireflies, consider taking a few photos, jotting down some notes (air temperature and humidity are especially helpful), and sharing what you observe on the Firefly Atlas! While the Atlas protocols are built around adult sightings, we also accept submissions for larvae, and will do our best to help you identify your species. The reality, though, is that we may only get to genus. Due to a lack of morphological studies, species in most firefly genera cannot be reliably identified based on their larval stages. Even so, your observations are a big help to researchers who are trying to learn more about fireflies—especially where they live, when they are active, and what they are eating. All of these data add up and form the foundation for developing effective conservation strategies for fireflies. After all, how can we conserve a species if we don’t know anything about what it’s doing for most of its life? The more we learn, the better we can ensure that fireflies have what they need to thrive throughout their entire lives.
###
Additional reading
For a deep dive into the world of larval fireflies, check out some of the resources below.
Archangelsky, M., & Branham, M. A. (2001). Description of last instar and pupa of Pyropyga nigricans (Coleoptera: Lampyridae, Photinini) and comparison with larvae of other Photinini genera. The Canadian Entomologist, 133(2), 155–164. https://doi.org/10.4039/Ent133155-2
Archangelsky, M., & Branham, M. (1998). Description of the preimaginal stages of Pyractomena borealis (Randall, 1838) (Coleoptera: Lampyridae) and notes on its biology. Proceedings of the Entomological Society of Washington, 100, 421–430.
Branham, M. A., & Archangelsky, M. (2000). Description of the last larval instar and pupa of Lucidota atra (G. A. Olivier 1790) (Coleoptera: Lampyridae), with a discussion of abdominal segment homology across life stages. Proceedings of the Entomological Society of Washington, 102(4), 869–877.
Buschman, L. L. (1984). Larval biology and ecology of Photuris Fireflies (Lampyridae: Coleoptera) in Northcentral Florida. Journal of the Kansas Entomological Society, 57(1), 7–16.
Buschman, L. L. (1988). Larval development and its photoperiodic control in the firefly Pyractomena lucifera (Coleoptera: Lampyridae). Annals of the Entomological Society of America, 81(1), 82–90. https://doi.org/10.1093/aesa/81.1.82
Buschman, L. L. (2019). Bioluminescent Behavior of North American Firefly Larvae (Coleoptera:Lampyridae) with a Discussion of Function and Evolution. Insects of Western North America, 11. https://api.mountainscholar.org/server/api/core/bitstreams/30ad7887-1f80-4e82-95b6-7f82ffcea474/content
Faust, L. F. (2017). Fireflies, Glow-worms, and Lightning Bugs: Identification and Natural History of the Fireflies of the Eastern and Central United States and Canada. University of Georgia Press. Athens, GA. 356 pp.
McDermott, F. A. (1954). The larva of Micronaspis floridana Green. The Coleopterists Bulletin, 8(3/4), 59–62.
Riley, W. B., Rosa, S. P., Lima da Silveira, L. F. (2021). A comprehensive review and call for studies on firefly larvae. PeerJ 9:e12121. https://doi.org/10.7717/peerj.12121
Waite, E. S., Keller, O., Tonyai, K. K., Smedley, S. R., & Branham, M. A. (2017). Description of the last larval instar of Ellychnia corrusca (Linnaeus, 1767) (Coleoptera: Lampyridae). Annual Meeting of the Entomological Society of America, Denver, CO.
Wenzel, H. W. (1896). Notes on Lampyridae, with the description of a female and larva. Entomological News, 7, 294–296.
