Fireflies
Visiting a firefly meadow on a summer evening is a memorable
experience, but what exactly do you see? How many different types of
fireflies are among the flashing lights? Can you tell if they are male
or female? Why are they flashing? What is a firefly, anyway?Blinking Beetles
Also known as lightning bugs, fireflies are neither bugs nor flies; they are actually beetles, which have two pairs of wings. The outer pair, called elytra, are hard and held outright during flight like the wings of an airplane. The softer inner pair beat to power and control the beetle's flight.What Do They Look Like?
Like all insects, fireflies have six legs and three body parts. The upper part of the middle segment, the thorax, extends over a firefly's head and is called the pronutum. Since they are creatures of the night, fireflies also have large eyes.Types Of Fireflies
There are approximately 20 - 30 species of fireflies in New England. Identifying them is not always easy, and there is consequently much debate over how many different species we have in New England. Sometimes the only way to tell two different species apart is to examine their internal organs – an experience most unpleasant for the firefly.Not all New England fireflies flash, but those that do come in three main genera (groups of closely related species):
- Photinus
- Pyractomena
- Photuris
Photinus
With about 15 species living in New England, the Photinus is the most common firefly to the area. Each is about one half inch in length, and it produces a yellow-green flash.
Pyractomena
Pyractomena is about the same size as Photinus, but its flash is often amber colored, like an ember flickering from a campfire. Its pronotum (head covering) has dark edges. New England has many fewer species of Pyractomena than Photinus.
Photuris
The Photuris firefly is the biggest of the three genera, about an inch long, with very long legs. It often has a slight diagonal line on its wings. The Photuris's dark-green flash can be more green and brighter than that of Photinus, but these fireflies are difficult to identify, and researchers are unsure of how many different species live in New England.Identifying Gender
Location
There are a few different ways to determine the sex of a firefly. The simplest way is to observe whether they are flashing while flying or while resting on vegetation. Typically, the males flash in flight while they are patrolling an area for females. The females observe from their perch and, if interested, they return the males' flashes.
Although looking for flashes from fireflies on a perch or in
flight is a good general rule for identifying the sex of a firefly, it
is not totally reliable. Males often begin the evening by flashing from
a perch before taking flight after sunset, and when they later land to
find a female, they continue to flash. In addition, Photuris females often flash while in flight. 
Light Organs
A more reliable method is to look at the light organs of the firefly. To do this, examine the firefly closely and carefully. If it is in flight, then you must catch it. Fireflies can be easily damaged by rough handling – learn more about how to handle a firefly.
For Photinus and Pyractomena fireflies, it is easy to determine their gender by examining their light organs. A male Photinus
can be identified by the last two light sections on his abdomen, while
a female has her light organ on the second-to-last segment.In Pyractomena, the male's light organ is similar to that of Photinus, but in the female, the last two segments have two small light organs, one on each side of the segment.
Identifying male and female Photuris fireflies is more
difficult since both have light organs on the last two body segments.
However, on the female, the area that produces light does not cover the
entire segment and is bordered by a translucent margin. With some
practice, you can pick out this subtle difference.Flashing Facts
Why Do Fireflies Flash?
All living creatures that sexually reproduce must attract a mate, and their mating behavior varies widely throughout the animal kingdom. For animals active in the dark, visual signals are not always possible, so they use other cues.For instance:
- Crickets sing.
- Moths use pheromones — a kind of animal perfume.
- Some spiders stomp their feet while others pluck the web threads. Daddy longlegs use touch.
It is up to the female to decide if she wants to mate with a particular male; if she doesn't respond to his flash, he cannot find her in the dark.
Playing the Field
How does the female decide which male to choose? During mating, the female firefly receives a "nuptial gift" from the male, which contains sperm to fertilize her eggs and food to help nourish them. Research on some species, including a local Photinus, suggests that the female is swayed by the brightness and duration of a male's flash. The more robust male firefly can produce a brighter flash and offer a larger nuptial gift, thus making him the preferred choice.The mating ritual can also be a perilous process — learn more
Different Fireflies, Different Flashes
To most people, the flash of one firefly looks the same as another. However, with the possibility of many different species living in a meadow at the same time, each firefly needs a method of picking out his or her own kind.Each species of firefly has a fairly distinctive flash pattern, which each differ in a number of ways:
- Color
- Length
- Number of flashes
- Interval of time between flashes
- Time of night they are active
- Flight pattern
Beware Of Impostors
When Imitation is Not Flattery
For much of the season, there are many more male Photinus fireflies in a typical meadow than females, and the competition to mate is fierce. A slower male may find his intended already occupied by a faster suitor, so when he sees his flashing overtures reciprocated, it's in his best interest to act quickly -- or is it?Female Photuris Imitating A Female Photinus
Impostors are common in most firefly meadows. Photuris females can imitate a number of flash patterns used by Photinus females.A male Photinus firefly may see this flash and approach with mating on his mind. However, when he gets close enough, the Photuris female, about twice his size, can seize and eat him.
Male Photuris Imitating a Male Photinus
The male Photuris can also play the role of impostor, imitating a male Photinus in hopes of tricking a female Photuris – while she's busy trying to attract a meal, he may be able to locate a mate.Photinus Males Get Wise
Occasionally, a female Photuris may give a faulty imitation of the female Photinus flash. This can scare off male Photinus who have grown wary of imitators. Some evidence suggests that male Photinus fireflies have even learned to imitate this faulty flash and use it to scare off other male Photinus fireflies from a receptive Photinus female, effectively eliminating the competition. However, much research still needs to be done before scientists fully understand the signals passed between fireflies.Poisonous Blood
Since adult fireflies advertise their presence by flashing in the
dark, and their larvae also glow when disturbed, they would seem to be
an easy target for predators. Bats, toads, and spiders can all spot a
firefly's illumination. However, fireflies and their larvae are not as
defenseless as they might appear.Reflex Bleeding
When attacked by a predator, some fireflies shed drops of blood (hemolymph) in a process called "reflex bleeding." The blood contains a chemical that is distasteful and even toxic to many predators.Studies have shown that predators soon learn to steer clear of fireflies. Some also shun perfectly palatable insects that have been painted with a glowing substance to resemble a firefly larva.
The predatory Photuris fireflies are not able to make this defensive chemical on their own, but they can gain the poison, and thus the protection, from the fireflies they eat. The poison is then passed on to their eggs and resulting larvae.
Environmental Factors
Why We Ask About The Details
There is much that we still don't know about what ecological and human-made factors affect firefly populations. The data you collect for Firefly Watch can help our researchers gain a better understanding of how the following elements influence the fireflies in your neighborhood.Location
To be most useful, a habitat site should be fairly small and cohesive. It should be no larger than the area you can see easily while standing in one spot. A backyard that includes shrubs and trees can be considered one habitat, but a pasture bordering that yard would be considered a different habitat.Lawn Care
Mowing
During the day, fireflies can spend a lot of time on the ground and may be susceptible to frequent mowing.Fertilizer
Researchers don't know what effect fertilizers have on fireflies. Many fertilizers contain both weed killers and pesticides.Weed killers
We don't know what effect weed killers (herbicides) have on fireflies.Pesticides
People apply pesticides to control insect pests, but pesticides also kill many non-pest insects. Firefly larvae — young fireflies — are not pests, but they are grubs that live in the soil and will come in contact with lawn pesticides, which target grubs.Adult fireflies may come in contact with sprayed pesticides, some of which are used on localized problem areas like trees. Others, like those targeting mosquitoes, are sprayed over a large area. Although it may seem reasonable to assume that pesticides have an adverse effect on firefly populations, we need data to prove or disprove this assumption.
Light Sources
House or Building Lights
Most fireflies find a mate by flashing. They must be able to see the flash of a prospective mate and return the flash. We don't know to what degree outside lights affect a firefly's ability to locate a mate.Streetlights
Streetlights produce a type of light different from house lights, and we'd like to determine if one type of light is more detrimental than the other.Nearby Water Sources
Firefly larvae live in the soil, and they need a certain amount of moisture to survive. In some areas, rainfall and shade may be enough to keep the soil moist. In others, the moisture may come from standing water, but we don't know how important standing water is to fireflies' survival, nor do we know how different types of water affect them.Flash Chart
Firefly Identification
Identifying fireflies is very difficult, even at the best of times, because many fireflies look exactly alike. As with many small insects, the only sure way to identify them is to compare some of their internal organs. This is a technique that goes beyond the scope of our study, and we do not ask our members to identify the fireflies they are seeing.However, since many fireflies communicate using flash patterns unique to each species, it is often possible to identify a firefly by its pattern. With patient observation, you can start to recognize the different fireflies in your habitat. Then, use this flash chart to identify the patterns you are seeing.
Download the Chart (PDF)
Notes About the Chart
Although using the chart to identify fireflies may sound like a simple process, please be aware of the following:The Chart Is Incomplete
There are approximately 150 species of fireflies in the United States, and the chart lists only a small percentage of them. It contains some Photinus, a few Pyractomena, and no Photuris . We will update the chart as more information becomes available, but for now, it is incomplete.Flash Rates Change With Temperature
As the temperature drops, the flash rate slows down. For instance, male Photinus aquilonius fireflies flash once every 5 seconds at 70°, and once every 11 seconds at 54°. Data for flash rates at different temperatures is scarce, so you will have to guess how much to adjust the flash rates to compensate for any difference in temperature from what you see listed in the chart.Not Each Firefly On The Chart Will Live In Your Area
It is possible that you might match your firefly to a flash pattern on the chart only to find out that the firefly doesn't live in your area. Unfortunately, range maps do not exist for many fireflies, but some can be found for Photinus fireflies in the pamphlet, "Studies on the Flash Communication System in Photinus Fireflies" by Dr. James Lloyd. Much of the information on the flash chart comes from this pamphlet; it contains lots of good information on over 20 species of Photinus fireflies.Photuris Fireflies Will Often Imitate Other Species
Some Photuris females prey on other fireflies, imitating the female of their prey species in order to lure males close enough to grab and eat. The only way to be sure that you are looking at a Photinus or Pyractomena firefly — and not an imitating Photuris -- is to catch it and identify it visually. Learn more about safe handling of fireflies.How to Use the Chart
In spite of these difficulties, it is fun use the flash chart to identify the fireflies in your habitat by their flash pattern.To identify your fireflies, follow these few steps:
- Time the flash pattern of a male firefly with a stopwatch. He will usually be flying. Record the timing of the pattern.
- Find a perched female that is responding to his signal and time that with a stopwatch. Record her timing.
- Catch both the male and female to determine whether they are Photinus or Pyractomena. Make sure you are not looking at an imposter Photuris firefly. Review types of fireflies.
- Find the flash pattern on the chart that most closely resembles your observation, taking into account the difference in temperature.
- If you have identified your firefly as a Photinus sp., check the range maps in Dr. Lloyd's report to make sure that firefly lives in your area.
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