You're not nuts, there are more lightning bugs than usual

I get migraines, and a few hours before a bad one hits, I start seeing small, flashing points of light in my peripheral vision. So, during dinner a couple weeks ago, when I caught a small, repeating flash out of the corner of my eye, I figured I was in for a nasty couple of days. Then I noticed my two cats were raptly tracking my migraine around the room. The flashes were from a lightning bug (interchangeably called “firefly”) that had somehow gotten into the apartment, a miracle bug/laser-pointer hybrid that appeared to blow everything the cats had experienced up to that point out of the water. 

When I mentioned this later, several other people related that they’d had a lightning bug get inside, too! None had ever had it happen before, either. Anecdotally, people agreed that it seemed like there were more fireflies than usual this year, but it was unclear how to verify that, or figure out why. Maybe Philly stopped using a pesticide in the parks? Maybe one of their natural predators was having a bad year? Maybe people were just noticing it more because the weather’s been so nice? 

“There are a lot more fireflies this year, I think pretty much everywhere, and that’s because it’s been a really wet spring,” says Sara Lewis, an evolutionary ecologist at Tufts University who’s done a lot of research on fireflies. In fact, she’s on sabbatical writing a book on them, Silent Sparks, due out from Princeton University Press next summer. “So many people are curious about fireflies. We’ve learned a lot about their evolution, behavior and chemistry over the past 20 years, but it’s mostly hidden away in the scientific literature,” she says. “With the book, I’m trying to translate science into plain English.” 

For example, Lewis says, if you’ve ever puzzled over how something as complicated as the firefly’s bioluminescent mating signals could possibly have evolved: “All of the scientific evidence points to the idea that firefly light first evolved in the juvenile firefly as a warning, like how monarch butterflies are brightly colored as a warning signal that tells potential predators, ‘Don’t eat me, I taste really awful!’” Since most nighttime predators can’t see colors, she says, “The light from fireflies first evolved as a way to warn nighttime predators, ‘I taste really awful!’ It wasn’t until later that that signal got co-opted by the adults for courtship and finding mates. 

“Believe it or not, there are fireflies everywhere in the U.S.,” says Lewis, “but not all those fireflies light up.” Plenty of species, sometimes called glowworms, never moved beyond the original “don’t eat me!” larval bioluminescence. Since the glowing larvae are underground most of the time, many people assume fireflies just don’t exist west of the Rockies. But while 2014’s bumper crop is most obvious on the East Coast, Lewis says, it’s likely happening all over the U.S., even if it’s only glowing underground.

Karen Verderame, invertebrate specialist at Philly’s Academy of Natural Sciences — she’s responsible for the museum’s live insect displays, and helped put together last summer’s “Glow: Living Lights” exhibit — has definitely noticed. Though there’s no way to say anything conclusive or scientific right now — “They may have that data a year from now, after doing all the surveying” — she says that entomology listservs and “the invert community” have been chattering about 2014 being a great summer for fireflies.

Verderame describes the ideal firefly habitat as basically a forest — tall grasses, bushes and shrubs, a good water source  and plenty of damp, rotting leaves, wood and mulch to lay their eggs in — which is why they do so well in damp, humid weather. “Philadelphia, in particular, has a lot of good forest area and has been improving a lot of gardens that make good habitat for fireflies,” she says, though if no rotting logs are handy, “some will make do with overgrown abandoned lots where there’s tall grass and weeds growing.” 

Any firefly boom in Philly this year is probably mostly because of the wet weather, says Verderame, but she sees other potential local factors. “People have been getting more connected to their environment, planting local species in their gardens, that could contribute. … Also, Philadelphia has done a great job improving a lot of their park areas and not using as much pesticide.”

Both Verderame and Lewis agree that the more developed an area is, the worse a habitat it is for fireflies, because they can’t escape. “Fireflies aren’t really very good fliers, and they don’t disperse very well; the larvae also live underground, so they don’t get around much,” says Lewis. Fireflies spend their whole life cycle within a fairly small radius of the place they hatched; if that habitat is destroyed, they aren’t good enough at flying to go find a new one. “If you’ve got a spot that’s good for fireflies and you do a lot of construction, disturb the soil — even if you put it back very nicely, like as a golf-course development, you won’t have fireflies there when you’re done,” says Lewis. “The fireflies are gone. They’re out of there, they’re dead.” 

Fireflies are also ill-suited to cities because of light pollution. Like many night-flying insects, they use the moon to figure out which way is up, says Verderame. “When a moth comes to a light, it’s going, ‘Ooh, shiny bright light! Are you the moon?’ It messes their navigation up. It’s no different for fireflies — when you have a lot of light, it confuses their flight patterns and communication signals.”

Light pollution is doubly rough on fireflies because “it obscures the signals that fireflies use to find their mate,” says Lewis. There are very few studies on the subject, but she mentions one look-ing at how artificial streetlights in a town in Switzerland appeared to affect a species of European glowworm. The females of the species don’t have wings; they attract flying males by climbing onto a low perch and displaying their glow. The Swiss study found that “females didn’t seem to pay any attention to the streetlights in terms of choosing their display spot. But the males flying around looking to find the females by their glow only searched outside the lights, in dark spots. That means that all the females under streetlights never got mates.”

You can see the firefly aversion to light even in areas where there aren’t streetlights, says Verderame. For example, her house in Montgomery County is lucky enough to have a backyard that borders some woods and an unmowed field; in the summers, she says, “Everything in my back is aglow.” In this comparatively natural setting, you can observe how firefly activity waxes and wanes in counterpoint to the phases of the moon. In the light of a full moon, “there won’t be as many out,” she says. “On the nights of a new moon, that’s when I take my 4-year-old daughter out, because they’ll be all over the place.

“They’re starting to taper off now; their peak season is from mid-June to right about now,” she said on July 9. “In August, you’ll see some fireflies, they’re probably the late emergers. But by the time you go back to school, you don’t see them anymore. Even now, there’s not nearly as many as there were a month ago.”

(emilyg@citypaper.net)