Fireflies in Our Backyard on a Summer Evening

Every summer, starting in early-mid June, we're treated to the magical sight of fireflies glowing and flashing during the warm evenings in our backyard and nearby woods and fields.  This summer in particular has been especially good for seeing fireflies where we live in southeast Michigan. 

The last question above, "what do they look like when they're not flashing", is one I can answer  from my own observations.   Fireflies very easy to catch and to see up close. Recently I've found a couple in our house and in my work studio  so I was able to look at them very closely (I found both in bathrooms, interestingly enough -- I think they were attracted to the moisture since we've had a very dry summer).   

Fireflies (or lightning bugs) look like rather non-descript "bugs" when they're resting on a plant during the day.  They're small, at least in our area - about half an inch long.    Click on the photos below to see these interesting insects in more detail.

There are many species of fireflies, but the ones shown in the photos below are the same as (or similar to) the ones we see in SE Michigan.   Fireflies are not "flies" in the entomological sense, but are really beetles (order Coleoptera) in the Lampyridae family.

The fourth picture shows a flying firefly with its abdomen hanging low.  It's easy to see how they could look like teeny Tinker Bell-type fairies, isn't it?  

Fireflies have a property called bioluminescense, which is the ability of organisms to produce their own light.  

Fireflies have a photic organ (light-producing organ) at the end of their abdomen.  The photic organ takes in oxygen, which combines with the chemicals luciferin and luciferase in a chemical reaction that produces light.  This is called a "cold" light, because the chemical reaction doesn't produce heat during the production of the light.  

(Contrast that with an incandescent light bulb, which produce 90% heat and only 10% light with the energy it uses!)

These photos show the white photic organ in a firefly. The first photo was taken with a flash, and the second is the glow from the firefly.

Photo credit, Wikimedia Commons

Fireflies flash to signal that they're looking for a mate. 

In general, you'll see the male fireflies lighting up as they fly.  The females stay put near the ground.   When a female sees the flash of a male firefly, and if she is ready to mate, she'll flash back.  They'll continue flashing back and forth to each other, like in a "call and response" dialog, until the male reaches the female.

Each species has a different flashing pattern, and they only respond to that pattern.

HOWEVER....some species of already mated females will then change their flash pattern to a different species pattern, luring in the male, and then...EATING it!   I guess that's a way of getting sustenance without killing off their own males (such as in praying mantises, in which the females eat the males after mating!).

Not all firefly / lightning bug species flash as adults.  In the United States, most of the flashing fireflies live in the east half of the country, while most of the firefly species that live in the west half don't flash. Perhaps those species find mates through pheromones, or by visual cues.   But all firefly larvae, and firefly eggs bioluminesce.

The glowing and flashing of the adults, larvae, and eggs also serve to warn other animals that they taste bad.

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Firefly (Lightning Bug) | National Geographic

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