Out of the Mason Jar: Firefly Communication

 

It is a summer evening. The blue dark is just starting to settle beneath the trees and the fireflies are beginning their nightly ritualistic dance across my front lawn. As a kid, I would see the fireflies flashing, and I was entranced. It seemed they were beckoning me, and I would oblige, chasing them across the yard as the sunlight waned. I’m not the first person to be drawn out into the dusk with their hands flailing at these bobbing lights. I’m not the first person who misinterpreted the flashes as something to catch, like bits of magic to be stored in a mason jar and stared at for hours once I brought it back in with me. When the younger me so fervently chased, captured, and stared at fireflies, I had no idea that I was falling prey to the very same hypnosis that entranced millions of people before me. It is a phenomenon many centuries old, that children, tourists, artists, and scientists alike are drawn to firefly light.

The Light Show, Great Smoky Mountains

While poets romanticize the insect’s self-produced light, or bioluminescence, into stanzas, scientists unravel the meanings and processes behind it through data collection. Over time, scientists gathered enough data to conclude that these individual flashes are merely syllables in a conversation between males and females of specific firefly species, wherein the female lures in potential male mates with a receptive flashing signal.Therefore, firefly bioluminescence not only captures humanity’s attention, but it also captures the attention of the fireflies themselves.

Hoping for love, male fireflies dart across fields, over lawns, and through forests, using their flashing lights to woo the females hidden in the shrubbery or forest litter below them. Each species of firefly emits light at a certain tempo, a beat that the male keeps so that the female can spot him in the darkness. Then, if a female finds a male attractive enough, she will beckon him to her by flashing in doublets. Across species, females tend to prefer males with longer, more consistent flashes, though a firefly flash’s physical qualities can vary depending on which species is emitting the signal. Brightness, color, the quantity of flashes, the overall rhythm, and the duration of each flash are all characteristics that change depending on the species being observed. Therefore, males whose territories overlap with another firefly species can easily tell which females they are compatible with by glancing at their flash patterns.

A tree aglow with male fireflies flashing simultaneously

Male fireflies sometimes band together and woo their women as a team, using simultaneously timed flashes. This synchronous flashing behavior is thought to be an evolutionary step toward more efficient courtship between males and females. Since there are so many males vying for a single female signal, this poses challenges for the female. Her signal can get lost and confused in the midst of all of these flashes, multiple of the wrong suitors may respond to a signal specified for a particular male. Also, the cacophony of incoming signals is overwhelmingly difficult for the female to receive, process, and interpret. This visual onslaught is known as photic noise. This is reduced when the males flash in synchrony. While it doesn’t prevent multiple males from responding to the female flash, it allows the female to easily interpret the signal given to her by a male group. Then, the males also respond as a group, becoming rivals as they compete for the female’s attention. As they near the female, they form groups around the female. These groups are known as “love clusters.”

Sometimes, however, female fireflies temporarily adopt the flashing patterns of another firefly species. The males who are tricked into responding are killed and eaten by the female who is pretending to be a potential mate. This interaction, known as aggressive mimicry, occurs between Photuris and Photinus fireflies: two species commonly found in the Great Smoky Mountains. Some individuals from these firefly species participate in kleptoparasitism, as well. Kleptoparasitism is the act of feeding off of another species by stealing their food. Photuris fireflies do this by responding to signals of distress from Photinus fireflies that are caught in spider webs. Scientists are still unsure as to what purpose the distress flashes pose for  the trapped firefly, however, the female Photuris firefly benefits because it makes the entangled male easier to spot. The female Photuris then rescues the Photinus firefly from the silky tangles of the spider web. However, the male Photinus firefly isn’t free for long, as the Photuris firefly proceeds to prey on him.

Photinus female preying on a Photuris male

It is proven that the female fireflies play this trick to protect themselves and their larvae. This is because the Photinus firefly naturally contains a substance that the Photuris firefly can only gain by ingesting the male victim. These substances, called lucibufagins, are known to repel potential predators from fireflies and their oocytes, or eggs. Participating in this bioluminescent trickery to obtain the substance, therefore, has many beneficial repercussions for the Photuris firefly.

It seems that the various patterns of firefly flashes can contain specific meanings and intentions. The firefly’s light patterns contain meanings that accomplish more than it may seem while watching the dazzling display from one’s porch. Like morse code, the light helps fireflies communicate. Also, a specific light pattern is a firefly species’ identity and trademark.  Bioluminescence helps the firefly woo its mates, prey on its own kind, and cry for help in times of distress. There is great scientific significance beneath what can seem like simple blinks and spurts of light in the summertime darkness. Yet, every once in a while, it is easy to fall into that trance. Pressing our noses up against the mason jar’s glass like amazed children, everyone can experience the magic for a little while.

Citations

  • Eisner, T., D.F. Wiemer, L.W. Haynes, and J. Meinwald. 1978. Lucibufagins: defensive steroids from the fireflies Photinus ignites and P. marginellus (Coleoptera: Lampyridae) Proc. Natl. Acad. Sci. 75:905-908
  • Faust, L.F. 2010. Natural history and flash repertoire of the synchronous firefly Photinus carolinus(Coleoptera: Lampyridae) in the great smoky mountains national park. Florida Entomologist 93:208-217.
  • Faust, L., R. De Cock, and S. Lewis. 2012. Thieves in the night: kleptoparasitism by fireflies inthe genus Photuris dejean (Coleoptera: Lampyridae). The Coleopterists Bulletin 66:1-6
  • Lewis, S.M., and C.K. Cratsley. 2008. Flash signal evolution, mate choice, and predation in fireflies. Annu. Rev. Entomol. 53:293-321.
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