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Today is Firefly Day!

Fireflies, Glow-worms or Lightning Bugs – these insects are amazing and they bring back childhood memories of trying to catch them in my grandparent’s  backyard. Oddly, they are neither flies, worms or even true bugs, they are beetles.  They are classified in the family Lampyridae in the order of, Coleoptera, winged beetles.  With over 2,000 species world-wide not all produce light, some use pheromones – a sort of insect perfume to communicate, but for those that do produce light, known as bioluminescence, it really is a pretty cool site. 

Fireflies are found on every continent except Antarctica. There are about 150 species found in North America with three primary groups of fireflies – Photinus – Greek for “shining”, Photuris “luminous tail” andPyractomena “fire”.  There are about half a dozen species in the eastern United States.  People will most likely see the common eastern firefly, Photinus pyralis, at night.  Photinus carolinus is the synchronous firefly species that produces the beautiful synchronized displays.  Great Smoky Mountains National Park is a firefly destination because of the synchronized fireflies. 

Why do they flash?  Most often it is done to communicate with each other and attract a mate.  It is also a defense mechanism to warn predators to stay away since they taste nasty and are toxic. The male Photuris will mimic the female flashing of the Photinus to attract the male over so it can eat it, this is called aggressive mimicry.  Photuris are called the “femme fatale fireflies”.

Scientists call fireflies light “cold light” because it produces no heat.  Almost 100% of the fireflies energy is emitted as light.  Incandescent bulbs emit 10% of the energy as light and fluorescent bulbs 90%.

The light producing organs are called lantern organs. The firefly produces light when the two chemical found in its tail, luciferase and luciferin, react with oxygen.  ATP converts to energy and emits the glow.  These chemicals are used in biomedical research.  Every animal has ATP in its cells in a relatively constant level.  In diseased cells the amount of ATP varies.  Luciferase and luciferin can be injected into diseased cells to detect changes.  They can be used to study diseases from cancer to muscular dystrophy.  They have been also used to detect life in outer space, as well as food spoilage and bacterial contamination on earth.  Luckily for fireflies luciferase and luciferin can now be produced synthetically, although some companies do still collect fireflies, to the detriment of the species. 

Each species has a characteristic flashing pattern, including the number of flashes in the signal the duration of the signal, and the time interval between signals, as well as differences in color and intensity.  In Connecticut, according to Firefly Watch, fireflies have been spotted from May 1 – August 11, generally they make a sporadic appearance in early June and they are out in full force a couple weeks later. The flashing tends to be more brilliant in the males although in some species only the females produce light.  The common eastern firefly begins flashing at dusk and generally stops when the sky gets fully dark, some individuals might continue flashing much later.

Different species occupy different areas – Photuris pennsylvanicus males are usually in the treetops and flash 3, 4 or 5 times, the females remain on the ground and respond by flashing 1, 2 or 3 times each period.  Their light is greenish-blue or pale-blue.  Photinus marginellis, usually inhabit low shrubs and the females are on the ground.  The light of this species is yellow.  Photinus pyralis stays closer to the ground and they flash a yellow light as they ascend

Fireflies go through a complete metamorphosis – egg, larva, pupa and adult.  After mating the female lays about 100 eggs under stones or beneath vegetation.  They can glow at all stages, even the larva in the egg will glow when disturbed.  They are eggs about 3 weeks, then spend most of their lives as larva, feeding and growing for 1-2 years.  During this time they will feed on insects, snails and slugs.  They inject juices into their prey that paralyze them and dissolve the body so they can suck up the juices.   They are a pupa for about 3 weeks, and becoming an adult.  They only live as an adult for 2-4 weeks.

Fireflies are truly amazing critters!   Perhaps you would like to try and learn the language of fireflies and “talk” with fireflies.  You can do this by going outdoors at night, observing the patterns and mimicking them using a penlight.  If you decide to capture them in a jar to observe them more closely, remember to only keep them in a jar for at most a couple of hours and then release them.  If you are just going outside to observe them it is best to bring a flashlight covered in blue or red cellophane so as not to disturb their flashing. 

There is a lot we know about fireflies, but still more to learn, for example researchers are still not sure exactly what triggers the flash and they are still studying them.  If you would like to get more involved you can join Firefly Watch, a network of citizen scientists. By observing fireflies in your own backyard you can help scientists map fireflies. 


Firefly Watch

Firefly Conservation & Research

The Fireflies Book by Brett Ortler – A fun, casual introduction to the world of the firefly.

Fireflies in Iowa YouTube 6:22

Fireflies Glowing in Sync to Attract Mates – National Geographic Video

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