Research Sheds Light on Mysteries of the ‘Shadow Ghost’ Firefly

Phausis inaccensa male and female

Phausis inaccensa belongs to the Lampyridae family, commonly known as fireflies, but in P. inaccensa‘s case the ones that fly (lantern-less males, as shown at left) lack “fire,” so to speak, and the ones with fire (females, right) don’t fly. (Photo originally published in Faust et al., American Entomologist, Fall 2017)

As a species of firefly, Phausis inaccensa doesn’t quite live up to the popular perception of glowing flyers lighting up summer nights. P. inaccensa males lack lanterns, and females, meanwhile, do glow, but they lack wings.

Hence their nickname, “shadow ghosts.”

Perhaps unsurprisingly, not a lot is known about P. inaccensa. But two researchers who have successfully studied the species offer a thorough profile of the mysterious firefly in “Bringing Light to the Lives of the Shadow Ghosts, Phausis inaccensa (Coleoptera: Lampyridae),” in the Fall 2017 issue of American Entomologist.

“The shadow ghosts represent a bit of a challenge because they are so very difficult to find,” says Lynn Frierson Faust, an independent researcher and co-author of the article in American Entomologist. “Yet, they are often literally right under our noses, living their lives—courting, mating, guarding their eggs, and surviving as seldom-seen larvae and pupae—as they have for long before we were here.”

Both males and females of P. inaccensa reach about 6 millimeters in length, though the females are neotenic, retaining a larva-like body into adulthood. At night, the female raises her tail to display her glowing lantern, attracting flying males. After mating, the female lays a clump of eggs and remains nearby to guard them until her death.

Phausis inaccensa female aglow

The larviform female P. inaccensa turns up her tail to display her lantern to attract males. (Photo credit: Ted Faust)

“The neotenic females like the shadow ghosts invest 100 percent of their energy into their one clump of eggs. No energy goes to wings or flight. They are fully, 100 percent invested in getting their eggs to be the next generation of shadow ghosts,” says Faust. “That such a tiny ‘primitive,’ vulnerable-looking female displays such determined, purposeful, focused behavior—well, it is amazing to me.”

Faust is also author of Fireflies, Glow-worms and Lighting Bugs: Identification and Natural History of the Fireflies of the Eastern and Central United States and Canada. Her report on P. inaccensa is a collaboration with Timothy G. Forrest, Ph.D., at the University of North Carolina-Asheville. Their combined research dates back as far as the early 1990s and describes populations of P. inaccensa observed in Mississippi and Tennessee with additional data from Arkansas, Pennsylvania, North Carolina, and Minnesota.

Phausis inaccensa female guarding eggs

The female P. inaccensa guards her clutch of 20-30 eggs for several days after laying them, until her death. (Photo originally published in Faust et al., American Entomologist, Fall 2017)

Suggested but not answered in Faust’s and Forrest’s research is the possibility that female’s egg-guarding behavior until death might be followed by matriphagy: “Could it be possible that these egg-guarding mothers’ bodies serve as the first meal for the newly hatched larvae? Future rearing experiments could leave the deceased mothers with their egg clutch to see if the eclosing larvae exhibit post-mortem matriphagy and thereby increase their survival,” they write.

“My main hope is this: Now others will be armed with a little knowledge and curiosity about these interesting fireflies,” Faust says. “I hope many additional local populations of all the Phausis species will be discovered, protected, studied, and appreciated. And, ultimately, we will all take another step forward in our understanding of the amazing insects of our natural world.”

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