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On Colorado Lightning Bugs…

Updated: Aug 12, 2023

Did you know that there's Fireflies in Colorado? There are... and believe it or not, there's actually fireflies in every western State!

Microphotus pecosensis male on tweezers. More about this species below...



I study fireflies, but I am an ant researcher primarily, so much of this knowledge is second hand from books and knowledge I have gained from talking to others in the feild.

That being said, here are two great resources I want to Highlight:


Basic Lighting Bug Info

Lightning Bug is a common name used in the US for Beetles in the family Lampyridae. It's essentially equivalent to the term Firefly but has lost much of its prevalence due to the term firefly picking up a sort of a "media spotlight" showing up in songs, movies, and TV shows. firefly is also a shorter term, which is one of the reasons it's often more used by those who research fireflies.

If the term firefly is so widely used, why would I use the term lightning bug instead? In fact, Lampyridae is a beetle family so why would I even want to use a term which isn't taxonomically correct (I study taxonomy after all)? When I interned at Discover Life in America one of my coworkers, Jamie, actually recommended an appropriate name Flash Beetle as a common name for fireflies. There are other glowing beetles (Elaterdae in South America, Phengodidae in the US) but they don't truly flash. In most situations, I believe that flash beetle is an ideal term, but I have solid reasons to use the term lightning bug.

Here are my reasons to use the term lightning bug to describe Colorado/Western fireflies:

  • Lightning is a daily occurrence in Colorado, and the spectacular storms and hail are a major part of our daily lives. It's almost rediculous how many times I have been caught in or narrowly avoided a rainstorm in the mountains.

  • In Kentucky (where we are attempting a firefly survey) there's not nearly as many lightning storms as there are out west.

  • The one Pyractomena species of Lightning bug in Colorado has multi-peaked flash trains, reminiscent of sparks or heat lightning. This gives them the common name "Wiggle Dancers"

  • In her book Fireflies, Lightning Bugs and Glow Worms: Identification and Natural History of the Fireflies of the Eastern and Central United States and Canada (which is probably one of the best resources for eastern fireflies ever made) Lynn Faust Laments on the subtle dissapearance of the term lightning bug and mentions that she wishes it had more prevalence. This could be a small effort on that front.

Given these inflection points, I have decided that by referring to at least Colorado Lampyridae as lightning bugs would be a fitting and well deserved title, although (as you will read later) it may not be entirely fitting for every species.


Lightning Bug Life Cycle

Like other beetles, fireflies are holometabolous, meaning they complete a full life cycle of egg > Larva (several stages) > Pupa > Adult. The thing that most people might not realize is that every firefly species glows, but not always as an adult. Firefly eggs, Larvae, and early stage pupae may glow. The primary identifying feature of Lampyridae is the fact that at some point in their lives they have a bioluminescent lantern. Essentially every larval firefly can glow, but there might be one ancestral species that doesn't glow as a larva.

A Sychronous Firefly (Photinus carolinensis) larva from the smoky mountains. The yellow lantern can be seen on the abdomen

Larval lantern glow can be seen on the ground at night. They usually emit a dim green/yellow glow underneath foliage, but at standing height, this glow often appears blue. According to Lynn Faust, Children often have the most accurate depictions of firefly flash colors, and can see the more dim lights of some species. In my experience, you can often mistake larval fireflies as having blue glows, until you bend down and see them up close. Some larvae line river banks and catch little midges and aquatic insects which are easily caught with the lantern.

Types of Lighting Bugs

As adults, fireflies take A few general "forms." The most common/most well known in the eastern fireflies is what I'll dub the "Flashing" firefly, where the males flash to attract a female mate and the females flash in response. Photuris, Micronaspis, and Pyractomena all fit into this category.

Pyractomena dispersa are flashing fireflies.

The "Femme Fatale" fireflies (Photuris sp.) also flash to mate like this, but the females also flash to attract male prey of other firefly species. In addition they will also flash vigorously if caught to scare of predators.

Photuris cf. versicolor female adult beetle, seemingly taken on a potato (just my cell phone though).

Photuris sp. larva and a leaf.

One of the more common western forms of firefly is what people mistakenly call a glow worm. The females of this firefly are what's called larviform, they have no wings and are often pink and grub like in appearance. The females glow and the males have huge eyes to find females. Microphotus and Pleotomus fireflies fit into this category. This term "Glow worm" is problematic, because it is shared by 3 terrestrial bioluminescent organisms in the US. The one that most deserves the title is a fungus gnat, but all 3 could conceivably receive the title. For this reason, I'm calling this firefly form a "Flash Light Beetle." It's a double meaning due to fact that their lantern is much like a flash light and that you can often find the males using a flash light.

A male Microphotus pecosensis "Flashtlight Beetle" type firefly.

Another form, The "Ghost" Firefly (genus Phausis) is unique, they're found in the Eastern US and are Similar to Flash Light Beetles, but the female is stark white and possesses several light organs which are concentrated in the head and abdomen. The most common species (while still being rare) Phausis reticulata, is well known because the males leave their lanterns on for a long period of time (14 seconds- 2 minutes). They are the only male fireflies that function this way. Not all Ghost fireflies have similar male flash patterns, and one is dark (not flashing). For this reason they are essentially "Flash Light" type fireflies, but P. reticulata has glowing males to make them slightly different. To recognise a female ghost firefly, look for a dim light on the ground, as you get closer to it it will split into two light spots.

The last group of american fireflies is the dark fireflies, which don't produce light as adults. Lucidota, many Pyropyga, and some Pyractomena fit into this category. These fireflies still glow as larvae. Many of these are decently common and can be seen as adults during the day.

Lucidota autra larva still glow (see the yellow lantern) this one was found in an Aphaenogaster nest. This ant-firefly interaction has not been recorded before.

(Synchronous fireflies are flashing fireflies)


Additional Biology of Lightning Bugs

This section will be sparse, because there are so many unique fireflies and so many great resources out there about them. Some western lightining bug biology will be covered below. I particularly recommend Fireflies, Lightning Bugs and Glow Worms: Identification and Natural History of the Fireflies of the Eastern and Central United States and Canada by Lynn Faust. This book is well illustrated and does a wonderful job treating the amazing diversity of the Eastern US Fireflies. The book's western counterpart is the Feild Guide Western North American Fireflies by Larry Buschman. This ebook is also great, and a draft is available online which is awesome!

All fireflies are predators as larvae. They live for the bulk of their life (~2yrs) as larvae. Adults (barring Photuris) only live a few weeks long. Some species overwinter as pupae for several months.

I often find lightning bug larvae in logs or under rocks. In samples from Papua New Guinea, they are are frequent among the winkler extraction leaf litter samples.

There are a few fireflies I neglected to cover from the US, including Anthill fireflies (Genus Pleotomodes). These beetles are a unique genus found in Florida. They were originally described flashing on ant hills, but tend to frequent ant nests and are found in the vicinity of ant nests. It's likely that these fireflies are myrmecophiles, meaning they live and develop inside ant nest and use the resources of host species to survive.


What Lightning Bugs Exist in Colorado?

Colorado has 6 Genera of Lightning Bugs:

  • The Femme Fatales (Photuris sp.)

  • Wiggle Dancers (Pyractomena dispersa)

  • Flash Light Beetles (Microphotus sp.)

  • Dark Elves (Pyropyga sp.)

  • Big Dippers (Photinus pyralis)

  • Black Lucys (Lucidota autra)

These 6 genera probably represent around 11 species if I had to guess. 3 Microphotus, 2 Pyropyga, and 3-4 Photuris. Photuris is the most speciose genus of fireflies out east, and several species are found within the versicolor complex and difficult to distinguish, there's also talk of a new species, Photuris coloradensis to be described. I don't know if that will happen. It frequents marsh and bog lands near Fort Collins. In terms of both Photuris and Microphotus, some (or most) ID is done by male genitalia dissection, so it's often more impractical to identify these, and can be harmful to the host populations. Preferred is a good macro photograph, and locations, time of night, dates, etc... this way a firefly scientist can go and collect vouchers.

At least 3 species are dark fireflies. Lucidota autra, Pyropyga minuta, and Pyropyga nigricans are all dark as adults. Male Microphotus are essentially also dark, because they have not been observed readily flashing with their tiny organs.


Species Profile: Microphotus pecosensis

Microphotus is the genus of Lightning Bug that southwesterners should know about. Particularly if you live in California, Utah, Nevada, New Mexico, Texas, or Arizona. They are unique, and I think males have particularly massive eyes for lightning bugs. It is the pink larviform adult females that make them the most intriguing however, although it doesn't necessarily make them unique. Even some Photinus fireflies have larviform females, but they have more developed head. Microphotus females are very similar to Phausis females, and the males are similar to Phausis males as well. This is not suprising however, as their life cycle is similar. The real mystery is why the males have a tiny lantern that they seemingly don't use.

Ant Flashlight Beetle (Microphotus pecosensis) male attempting to flip over.

I am designating the name Ant Flashlight Beetle, because we found males coming out of Camponotus nests. This was an odd observation but not the first time I have seen unobserved Firefly-Ant Interaction.

Both Males and Females of this species have a lantern, but males do not flash related to reproduction. The male flash is tiny and very weak.

A shot showing the ventral side of the male, another male is grabbing onto the small lantern organ.

Male Microphotus pecosensis with 'windows' on pronotum for better visibility. Combined with the almost entirely clear rim and large offset eyes, the male is well equipped for finding the female's faint glow. Much better than I was at least...

Microphotus male on the black light sheet. this one has a damaged pronotum.

A Microphotus Male on My Hand.

A Carpenter Ant Flashlight Beetle (Microphotus pecosensis) on the black light.

One of the best shots I have taken, of a Microphotus pecosensis male attempting to take off from a pair of rubaris 5 forceps.

The female of M. pecosensis is pink and larviform and produces a green grow. Like most flashlight beetle type fireflies, they are low to the ground and under foliage, making them difficult to find.

Female Microphotus cf. pecosensis bettle on wood. Image from iNaturalist.

My Observation

Various Microphotus observations


Species profile: Photuris Versicolor

Photuris is one of the more commonly encountered genera of fireflies in Colorado. So much so that it is reported by not one, but at least 8 separate news outlets (as a quick google search revealed to me. Their behavoir is intriguing, and it is what gives them their common name: the Femme Fatales.

Photuris cf. versicolor female adult beetle, seemingly taken on a potato (just my cell phone though).

Female Photuris lightning bugs are predatory as adults. This is unique amongst fireflies, as many often have very reduced mouthparts as adult beetles. In the case of Photuris, the predation is taken to an almost extreme level. Female P. versicolor complex fireflies attract a mate with their lanterns, just like any other female firefly... except it's usually not their own species they are attracting. The Photuris females then eat the unfortunate males lured in by their photonic siren song. In the case of Colorado Photuris, the female's flash seems to be to attract and eat males of their own species. The other type of readily flashing firefly, Pyractomena, does not appear in most of the places where Photuris have been found.

An Inaturalist Observation (not mine)


Species Profile: Pyractomena Dispersa

In Colorado, and out west in general, this species is referred to as the "wiggle dancer" firefly. Their eastern counterparts (likely a different species) are known as "Marsh Flickers." Both species require marshy habitat, as do many of our flashing fireflies. This species range appears very sparsely documented, but it appears that there is certainly a population in and around the San Juan Mountains, and Near Gunnison National Forest. Apparently this species flashes around July in Colorado, which is Odd because it's eastern Counterpart flashes in May.

Pyractomena dispersa males from Morehead, Kentucky. One tries to take off, and the other can be seen with an indented elytra. It was attacked by a spider before being collected, and miraculously survived at least an entire 7 days after being collected.

Kentucky Marsh Flicker Males, showing abdomen and huge reflective lantern. Notice how they look remarkably similar to an LED.

Another shot of P. dispersa from kentucky. Neither are females, which have longer abdomens and 4 tiny spot lanterns.

P. Dispersa male on grass, Some males fly through the air with their sparking light pattern, others flash from the ground especially once it gets colder.

A shot showing the dorsal view of a Pyractomena dispersa marsh flicker male from Kentucky. In Colorado this species prefers the name "Wiggle Dancer" the two populations are likely different species.

Female P. Dispersa have different shaped lanterns and bodies than the males, they tend to stick close to the ground. When the female sees an appealing male flash, she discreetly flashes from the underside of foliage to attract her mate. Usually multiple males recognize the flash, so they approach her.

Attempts at mimicking flashes.

If you study female flash patterns, you can theoretically mimic them to attract males like Photuris females do. This is often very difficult and requires a small light to do properly. When I was in Florida, my regular flashlight was able to attract micronaspis floridana (keys firefly) but it was rather hit or miss. In Kentucky, I used a small size pen light and my fingers to attract the Pyractomena males, I had little to no luck. I couldn't quite figure out what the female flash looked like, and the multi peaked flash made it extremely difficult. Plus I think the light needs to be more amber colored. I have tried this technique in the smokies with the synchronous fireflies, and had marginal to no luck, but observing the female flash was much easier. It is easy to attract flashlight fireflies, as they show up to flashlight beams and black lights. With little green LEDs you could probably attract them as well.

The Plight of Western Lightning Bugs

Unfortunately, most insects seem to be threatened by something these days. Fireflies are no exception. In the case of firefly decline, there is a much more readily available causes (and by proxy a solution) to population decline across various species.

The Problems:

  • Light Pollution

  • Larval Casualty

  • Habitat Loss

Light pollution is a major driver in most firefly decline, especially since these species are so dependent on light to survive. The effect goes much further than just fireflies however, devastating almost every nocturnal flying insect in some way. This problem, has a easier solution than many of the others, and it is changing out the spectrum of your lights. Unfortunately, there also has to be a change to streetlights as well, and that is a much more difficult sell. For some reason, Blue/purple Streetlights are popular in some areas. This has low effect on fireflies, but it endangers ant, lacewing, and moth populations (all crucial to environments). Red lights are ideal for preserving most insect populations, and for viewing the stars, but a lot of people worry that their house will look like a red light district. A much more readily accepted solution is a more yellow/orange colored LED bulb (Like these Un-Edison Bulbs). This provides residents with a normal light to help address the light pollution issue. But to better protect fireflies, one should also try (whenever possible) to prevent the light from spreading out and lighting up something that doesn't need lit up. An example of this is a garden, a garden does not need lights at night, and insects probably appreciate the lack of lights in a garden. A path going through a garden can probably be lit, but the lights should be directed downwards towards the path only and not on the foliage around it.

The results of the damage that light pollution causes can be seen when you go into a dark sky preserve. If you sample for insects in one of these areas, you can collect so many nocturnal insects, even with horrible gear. Insect populations are "happy", and environments tend to be healthy as well. So this is one of the most important changes that YOU can make that will help contribute to fighting insect decline. But don't just stop at your house, try to convince your neighbors to switch to bug lights. If you want to do more than this, see if you can get your streetlights changed to LEDs that point downwards (The lantern style ones are horrible for the environment). Generally, LED streetlights work way better anyways.

Larval casualty is mostly caused by trails and roads. There is not much you can do to prevent this, but if you walk somewhere instead of biking or driving, you can be aware of insects on the road or sidewalk and avoid stepping on them. The Smokies had to take this into consideration when they used to have trollies for the firefly viewing at elkmont. Trollies would kill lots of firefly larva and eventually contributed to population decline over time. This solution is not really a practical one, but the only thing it might influence is biking vs hiking. You have much more control over where you walk then where you bike. Most people aren't biking at night, but my recommendation is that you do not bike at night.

Off road vehicles cause more damage than anything else, so if you can drive on a road, do. Don't off road until you absolutely have to.

Larviform females fall victim to similar casualties as larvae, including Microphotus, so it is important to also keep in mind this fact. Another thing that can cause firefly casualty is livestock trampling females, so keeping some areas free of grazing may help save firefly populations. Such regions probably also help to foster pollinators which results in more fertile land

Habitat loss is a hard problem to solve, but not impossible. One of my former bosses, Will Kuhn, embarked on a rewilding process to start growing more native plants in his backyard, and has observed over 1000 species of insects in his backyard since starting this project. Other entomologists have done things like this as well. In the case of fireflies, they often live near marshy, wet areas, or near running water. So wetland conservation is helpful to preserve fireflies. Firefly Ranch (in Pagosa Springs, CO) deliberately keeps the wetland areas of their property wet, and that results in better firefly displays. If you have large property, or any property that you can plant native plants, this can inadvertently help fireflies. Fireflies are predatory, they need healthy prey populations. Several fireflies eat snails, so keeping wet areas around where snails would thrive may help firefly populations. Not draining wetlands on your property is very important to firefly preservation.

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