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Fireflies talk to each other by coded blinking patterns

Sunday, July 28, 2013
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This is the Pennsylvania firefly, one of the most common firefly species in our area.
This is the Pennsylvania firefly, one of the most common firefly species in our area.

My friend Kyle requested a column on fireflies. Since the firefly season (which has been spectacular this year) is almost over, I decided I’d better get to it. So, Kyle, this one’s for you.

What could be a more iconic image of the summertime experience of children in the Northeast than the joyful pursuit of fireflies on a warm summer evening? When I was a boy, I spent many a night contentedly gazing into a canning jar filled with fireflies by my bedside. As I watched the insects blink, my mind would wander with happy thoughts as my eyelids got heavier and heavier. Good times!

What I never understood as a boy was how complicated the world of fireflies actually is. Bioluminescence is an incredible solution to the problem of communicating at night. Male fireflies blink out their Aldis Lamp love songs in perfect silence and females blink their responses in return. I cannot help but think of WWII era warships cruising the oceans and communicating in similar fashion.

Extensive family

But wait, there’s more! In North America, there are 136 species of fireflies that are divided up among 20 different genera. In fact, there are so many different types that they have warranted their very own Family (Lampyridae). With so many species doing so much blinking, it should be obvious that there was a real possibility of some fairly massive confusion.

Hopefully, it should be equally obvious that the different species solved this problem by adopting their own coded patterns of blinks. The timing and duration of blinks is paramount in firefly communication.

Skilled entomologists can identify firefly species by these blinking patterns, but the rest of us mortals have to focus on morphology. The members of the firefly family share some distinctive features, but slight variations of this general theme allow precise identification. For instance, when seen from above, the heads of fireflies are obscured by a flattened “helmet” of shell called a “protonum.”

All beetles have a protonum, but its extension to cover the head, the way the bill of a baseball cap extends out over your face, is common in fireflies. The photo I have provided shows the antennae of the firefly sticking out from under the protonum. Each genus has its own protonum shape and color scheme.

Most insects are equipped with two pairs of wings, but in beetles the front pair serve as protective shells. Scientists call these specialized wings “elytra.” The different firefly genera all have slightly different elytra configurations, which helps in identification. These clues, and others too numerous to mention here, suggest that this firefly is Photuris pennsylvanica — the Pennsylvania firefly.

Adults in the Photuris genus are predators that will eat snails, slugs, and the soft-bodied larvae of other insects. However, females of the species Photuris fairchildi will also change their blinking pattern so they appear to be females from other genera. An optimistic male from the genus Photinus, say, may zip in with confidence because he thinks he’s about to get lucky, but everything changes when he finds open jaws instead of open arms.

Season ending

The breeding season of our fireflies, whether they be Photinus or Photuris, will end shortly. If you have any chance at all, I would encourage you to go out at night and try to catch a firefly. Take advantage of this very simple childhood pleasure, which turns out to be a very complicated, but effective method of looking for amore in the world of beetles.

Bill Danielson is a professional nature photographer and author living in Altamont. Contact him at www.speakingofnature.com.

 
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