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Nature's Magical Little Night Lights

By Adrian Higgins
Thursday, July 26, 2007

Here's one good reason to stay around here in the heat and humidity of summer: fireflies.

Mention of these insects inevitably rekindles fond childhood memories of collecting fireflies, or lightning bugs, in jam jars and watching their abdomens fizzle and glow. But forget the nostalgia for a moment and consider: Are they any less wondrous now that we have grown up?

I like to sit on the porch to watch the show. As the dusk descends, the catbirds slink off and the bats take to the air, silhouetted against the dimming sky. Then the fireflies -- which are actually not flies at all, but beetles -- use the black-eyed Susans as launching pads for their aerial displays. The males maintain a fiery dance to lure female beetles on the ground, which flash back. Even in a garden in light-polluted suburbia, a lone, distant firefly can catch the eye.

We explain the science of this phenomenon in the accompanying graphic (see Page 5), but even knowing how it works doesn't diminish its wonder. Michael Weissmann, president of a firm that consults on butterfly houses and insect zoos, is never blase about fireflies. "No, they're amazing creatures, to create light without heat; it's something we can't do." As an entomologist, he may be a little biased, but not much. He is from Colorado, which is mostly firefly-free, but he remembers them fondly from when he paid childhood visits to his aunt in Chevy Chase.

The creatures do not settle in arid climates, needing to live where there is moisture in the soil. In the United States, they are found mostly east of the Mississippi River. The beetles live in the ground, feeding on worms, slugs and snails. It is not entirely certain what -- or even whether -- they eat as adults, but research has suggested pollen.

"For us in Colorado, who never get to see them, the appeal is phenomenal," Weissmann said.

In the age before electric light and urban light pollution, our eyes would have found these flashes even more brilliant. But the beetles themselves don't seem to flee illuminated suburbs; indeed, you can get one to glow by mimicking a mate with a flashlight. But there are things that will kill them off, particularly garden pesticides. Treat your lawn for unwanted grubs and you will harm the larvae of the firefly species. Herbicides and fungicides may have an effect, too.

And consider mowing practices. The beetles spend the day at soil level and emerge at dusk, so mowing then could reduce numbers, as would repeated close cuttings of a manicured lawn.

Apart from robbing yourself of the summer light show, you are losing an ally. The beetles go after scale insects, aphids, whitefly nymphs and other garden pests, said Casey Sclar, an entomologist at Longwood Gardens in Kennett Square, Pa.

In homage to the insect, Longwood organized five child-oriented "firefly nights" this summer to allow visitors to catch and release the beetles and learn more about them. The events are staged in firefly-rich areas on the 1,050-acre estate, including the old orchard. The final two nights will be held on Aug. 10 and 21, starting at 6:30 p.m. ( http://www.longwoodgardens.org).

Nature photographer William Burt has communed with fireflies for years, but he knows that they can be hard to capture on film. Species that are dimmer, or don't blink for as long as others, he said, make for shy subjects.

In his new book of wetland images ("Marshes," Yale University Press, $35), Burt takes readers to a great sedge marshland in Douglas, Manitoba, and an evening 14 summers ago when he captured hundreds of fireflies signaling to one another. Another force of nature, lightning, is dancing in the distant horizon.

"There is drama and counterpoint between the enveloping darkness and these little voyaging lights," he said.

To capture the ghostly scene, he set his large-format film camera to have a large aperture and a long exposure. "Those lights appeared over 30 seconds; you collect images," said Burt, who lives in Old Lyme, Conn.

The fireflies provided the opening act to an amazing cabaret as the marsh birds began to sing to each other in the twilight. The lightning, with its searing force, added further drama. By contrast, the fireflies were weak and harmless. But alive.

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