There is something about fireflies that is undeniably enchanting, and I looked forward to seeing them here in western Massachusetts. They occur in Arizona, too, albeit different species restricted mostly to riparian (streamside) habitats. Back on the evening of June 17, I looked for fireflies and other insects around the schoolyard here in South Deerfield. I was not disappointed.
The fireflies I came to know from my days in Cincinnati, Ohio, are largely crepuscular species, most active at dusk. Here, they appear to be active only after dark. Still, they ready themselves in the waning hours of daylight, appearing more out in the open on foliage along the edges of forests and fields.
The first firefly I encountered was a species of Photuris. It has been recently discovered that there are several cryptic species which can only be identified from subtle differences in their flash patterns. Morphologically, and apparently even genetically, they are otherwise identical.
Photuris gained infamy decades earlier when it was revealed that the females of one species, P. pennsylvanica, habitually mimic the flashes of female Photinus pyralis, thereby attracting the males of that other species. The male Photinus, no doubt optimistic at a positive response from a potential mate, alights to find the large female Photuris to be in the mood for something else. She devours him. Literally.
Dr. Thomas Eisner of Cornell University was the gentleman and scholar who not only discovered this behavior, but learned why it occurs. The father of chemical ecology, Dr. Eisner deduced that Photinus fireflies produce potent defensive chemicals called lucibufagins. That’s correct, the compounds are steroidal pyrones related to toad toxins. The Photuris fireflies, however, do not produce this chemical, instead acquiring it through the consumption of their cousins.
As darkness began to descend, along with hordes of hungry mosquitoes that made continued searching unpleasant, if not nearly intolerable, I managed to spy a female Photinus, perched on a grassblade. I would need my camera’s pop-up flash to illuminate her, but what I didn’t expect was her reaction to it.
After my flash would go off, which must have seemed like the sun exploding to the poor girl, she would twist her body and return the flash, though infinitely dimmer. Now it was obvious that she thought I was the male firefly of her dreams. Any male capable of producing that bright a light must be the most genetically fit of all her kind. I found it fascinating that she would purposefully direct her flash as well. There was no question where she was aiming it.
Try as I might, I could never catch her own signal. My flash simply failed to recharge in time to capture her faint greenish glow. It was a miracle I could even catch the literal tail-end of her contortionist performance with a subsequent shot.
I was recently asked if only the male fireflies fly and flash, and it appears to be true of at least a few species. It pays females to keep a low profile in grass or foliage, since they invest heavily in the production of offspring. Males are more “expendable” in the genetic sense, though anyone who has tried to catch flying fireflies knows just how futile an exercise it can be.
I enjoyed my game of “firefly tag” with the lovely female Photinus, but fearing she may not have enough battery life to reply to real males, I eventually let her be. Please share your own firefly encounters, and watch this space for future posts on fireflies, and the book about them that I have brewing….