Swat team

Getting the buzz on nighttime insects

by Sally Cragin

"The light of the firefly is sufficient for itself only."

-- folk saying

You'll see plenty of insects during the day, but only at night do the musicians and artists of the invertebrate world appear. Crickets chirp, mosquitoes whine, and lightning bugs illuminate the inky darkness in a determined search for romance.

Already we're a month past the solstice, but there are plenty of species still eager to reproduce -- at drive-ins, under the stars, or around the porch light. But none has so touchingly cheerful a story as the humble and spectacularly gifted lightning bug. No New England childhood is complete without an episode of firefly collecting. These nocturnal critters prefer meadows or a shady, damp place where the grass is tall. Go out one evening and try and catch one. And then try and catch another. If it's too cold, the bugs will fly tantalizingly overhead; too warm, and they're too fast.

"There are approximately 124 species of fireflies in the United States and Canada, and probably 15 to 20 species in Massachusetts," says Linda Cocca of the Audubon Society. "Two common firefly species found in Massachusetts are the Woods Firefly [Photuris pennsylvanicus] and the Common Eastern Firefly [Photinus pyralis]."

Unfortunately, the number of fireflies -- though not the number of species -- appears to be diminishing, mostly due to "the decline and development of fields," Cocca says. In the past 150 years, much of the state's farming area has been reforested or developed.

Yet around this time of year, it shouldn't be too difficult to observe fireflies, which actually aren't flies at all, but soft-winged beetles equipped with a specialized abdomen that emits a heatless, yellow to green to blue light -- some species glow in colors that our eyes can't detect -- the glowing result of a complicated chemical reaction (the oxidation of luciferin).

The Greek philosopher Diogenes may have wandered the dark, late-night streets of Athens with a lantern searching for an honest man, but the firefly is more ambitious. Both males and females of the pyralis species, for instance, have a flashing pattern recognizable to one another. The male will emit a burst of light every six seconds, while the female pulses two seconds after the male. They will continue this pattern until they find each other. But not every firefly is willing to play by these rules. Females of the photuris family have learned how to mimic the responses of other species. Potential suitors fly in and are promptly eaten. Yet other fireflies have adapted methods of avoiding capture -- either by flying at twilight, so that they might recognize potential assailants by size, or by changing their flash signals to an extra-long measure. But it's a female market out there: males might spend days looking for a partner, while females need search only minutes.

That magical evening hour, which some poets refer to as "the gloaming," may be a boon to suitors hoping to avoid predatory female fireflies. But for humans, dusk is often accompanied by the sound of hands slapping flesh. By far, the most successful of the evening's sharpshooters are mosquitos. As we all know, females require a blood meal before they lay their eggs, and the search for flesh only increases as night draws near. The insects respond to "a certain light level in the evening, when they cue in to carbon dioxide coming off a host," according to Ken Simmons of the state's Division of Fish and Wildlife. "When we have a dry spell we have fewer mosquitoes, but there are periods when you always get high numbers -- in the springtime." If you've noticed more mosquitoes not long after a soaking rainstorm, you're not mistaken. Certain species of floodwater mosquitoes "respond to flooding conditions in a field after a thunderstorm, and their eggs are triggered to hatch so you can have an influx, where two days earlier there were none."

How much less sinister and annoying is the cricket? Mother Nature took more trouble with the cricket than the firefly, as there are some 1000 separate species in North America (granted, this does include grasshoppers and katydids), though she gave musical ability only to the males. Everyone can recognize the characteristic "trilling" (actually "stridulation") these creatures make, but range of meaning ascribed to this music-making is vast. Crickets chirp to attract a mate to warn off a rival or to claim territory.

Interestingly, we're heading into the peak choral season for the outdoor symphony.

In Massachusetts, the two most common species include the Field Cricket, which most entomologists actually think are two separate fall and spring species, and the Snowy Tree Cricket.

Pale green and not quite an inch long, the Snowy Tree Cricket prefers deciduous woods and forests, and will advertise at length for a mate. This Pavarotti of the glade makes a memorable and quite pleasant liquid trill that starts around dusk and continues throughout the evening. He will continue to chirp even after being chosen by a female -- she has to nudge him to get him to stop. "Thoreau referred to it as the `sound of slumbrous breathing,' " says Chris Lahey of the Audubon Society. "And for most people it's the sound of the summer night."

Observing nighttime insects is as easy as stepping outdoors (well-doused with Deet-laced insect repellent, of course). If you want to try a challenging auditory experiment, try and distinguish one cricket's chirping, and then see whether it changes or stops depending on any follow-up harmonizing. If you can pluck one trill from the grassy choir, you might consider a career as a conductor. Or try to follow the path of one firefly in the glowing connect-the-dots collage. But don't try and count the number of mosquitoes that you swat while you're out there -- it's a number too depressing to contemplate.

Sally Cragin thinks mosquitoes are a reasonable tradeoff for the pleasures of living near a pond.

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