June 21

Just after sunset, in the periphery of the yard, where the woods begin, the fireflies are beginning to flash. It is tentative now, with only a few early callers, though it will progress each night for a couple of weeks as more join in signaling to one another.

In the waning light, it is enjoyable to chase them, with jar in hand at the ready to hold them. They are tricky to capture, a flash there . . . run over to where it occurred . . . nothing, but a little further on . . . another flash. It is a game of chase we play, regardless of one’s age.

We are fortunate to have these yearly harbingers of July, for I understand that the firefly populations are diminishing in places of the country where they’ve been established for generations. No one is certain, but hypotheses center on global warming shifts, urbanization, and over use of herbicides. These are the usual reasons trotted out to account for the notable loss of biodiversity within the past twenty years.

Bioluminescence is the term for the creation of light by an organism. Fireflies and glow worms are the most commonly known terrestrial examples, and there are numerous aquatic organisms that engage in it. It is a cool light, meaning that no heat is produced to speak of, unlike combustion with which we are most familiar.

Like most bioluminescent organisms, fireflies use it for signaling a mate, where the female “calls” in a particular pattern, recognized by an attendant male who signals in a different, yet familiar return. In the enveloping darkness, I imagine males and females signaling and searching, each playing their own version of firefly tag.

On a given night, there may be more than one species, and this is where things get interesting, as the signal calls are species unique. Photuris species signal in a given pattern, and Photinus species have their own. Imagine this as you observe the back yard, when dozens of fireflies are signaling. It is difficult enough to search for a single firefly, let alone discriminate between competing patterns.

It is here that mimicry also takes place in a fascinating way. The female of one species mimics the mating pattern of the female of the other species, for the purpose of luring the opposing male. Upon being duped, the male finds himself attacked and killed by the assassin female in her way of furthering her own species. Amazing really.

The light is created by a protein contained in the abdomen of the beetle, called luciferin.  When luciferin is combined with another protein, the enzyme luciferase – which cuts luciferin, a chemical reaction takes place that releases photon energy (light).

All of this is happening in the backyard just now, and we will enjoy the show for the next few weeks.

Notes:

Bird’s foot trefoil going to seed

King Devil and Orange Hawkweed going to seed.