Fireflies
By Arwin Provonsha
General Information on Fireflies
Fireflies, also commonly known as lightning bugs, are neither flies nor true bugs, but are beetles belonging to the family Lampyridae. Worldwide there are over 1900 species. They are found on every continent except Antarctica. There are over 170 species in North America. Most are found only in the eastern half of the continent.
Not all fireflies flash. Some species are dayfliers and find mates with pheromones (chemical attractants) rather than flashes. Those that flash are generally called "lightning bug fireflies" and those that do not flash are called "dark fireflies."
The larvae (immatures) of all known fireflies also have the ability to produce light, even those which do not have the ability to flash as adults. Rather than flashing, they leave their lights on as a constant glow, which can be turned off if disturbed. The larvae, commonly known as "glowworms" can be seen along riverbanks and on moist soil in wooded areas from early to late fall. They overwinter in this larval stage and pupate in the spring.
Different species have different preferred habitats. Many are found primarily over open fields, others occur only in wooded areas, and some reside near bogs and marshes. Some flash primarily at dusk and stop when it gets dark, while others do not begin flashing until it is very dark and continue well into the night.
How do fireflies flash?
The firefly's living light is a chemical reaction, known as bioluminescence, in which visible light energy is released. The reaction involves the oxidation (a chemical burning) of luciferin, the light emitting molecule; luciferase, the enzyme that catalyzes the reaction; oxygen, which provides the burning energy; and magnesium, which facilitates the reaction. The emission of a flash is triggered by nerve impulses to the lantern.
Much of what we know about firefly flash chemistry was discovered in the 1980's at the Department of Entomology at Purdue University. Luciferin can now be synthesized and is used in the common glow sticks. It also has several medical applications.
Why do fireflies flash?
The males are the ones that we generally see flashing while in flight. They are doing it to attract the attention of females. Females generally sit in the grass or on top of taller weeds. If responsive to the flash of a particular male, she will respond with a flash of her own. He will then fly down to her and mating takes place shortly thereafter.
How can different species tell each other apart?
Some species are easily distinguished by size, coloration, and other physical features. However, many others are virtually identical. Those that look very much alike physically, tend to have different flash patterns. For example: One species has a long, steady flash lasting from 2-3 seconds with a 2-3 second pause between flashes; another has a very short flash (like a flash bulb going off) that is repeated every 2 seconds; while another flashes 3 short flashes in rapid succession with a 3-4 second pause between sets, while still another has a dot-dash pattern (short flash followed immediately by a longer one). There are many other variations as well.
The color of the flash also differs from group to group. For Example, species in the genus Photinus have a yellow flash, those in Photuris have a green flash, and those in Pyractomena have an amber flash. However, it may be difficult to distinguish these colors when they are in flight.
The different flash patterns and flash colors help the different species to tell each other apart, thus minimizing attempted mating with the wrong species.
Part of the fun of firefly watching is learning to distinguish the different types of flashes and figuring out their specific habitats. Very few species have common names. Most are known only by their scientific name.
Are fireflies harmful or beneficial?
Generally they are beneficial. Not only are they one of the great wonders of nature, making our summer evenings more exciting, but they are also predators (both as larvae and adults) on slugs, snails, and the larvae of a number of destructive insect pests of crops.
Adults of the genus Photuris (referred to as "Tiger Fireflies") are predators on other fireflies. The females can mimic the response flash of other species, thus attracting males who think they are in for an evening of romance, but get eaten instead. These tend to be the largest of our firefly species and can be distinguished by the two pale stripes running down the middle of each wing cover. Their legs are also much longer than those of other fireflies and can run quite rapidly. These are the fireflies that light up when placed in a jar. Most other types will just sit there doing nothing.
What is the most common firefly?
The "Big Dipper" (Photinus pyralis) is commonly found in North America. It is the firefly that is often seen over lawns in urban areas and along roadsides in the country. It has a yellow flash that last from .50 to .75 seconds. It tends to fly upward, sometimes in a "J" when flashing. At the end of the flash, the male hovers for approximately 2 seconds waiting for a female response. If there is no response, it will fly to a new location and try again. If you have a pen-light, you can sometimes lure a male Big Dipper by responding to his flash within the 2 seconds that he is hovering near you. Although easy to catch, Big Dippers do not tend to do much flashing when placed in a jar.
How can I learn more about fireflies?
There is a wonderful and informative newsletter called the "Fireflyer Companion" which is published a couple of times a year. It is available free of charge to interested students, parents, teachers, and naturalists. Write: Fireflies, Department of Entomology, Bldg. 970 Hull Road, Univ. of Florida, Gainesville FL, 32611.
Arwin Provonsha is the Curator of Collections for the Department of Entomology at Purdue University. He is also a scientific illustrator and a taxonomist. His current research involves the taxonomy, distribution, and flash behavior of the Fireflies of Indiana.
