INDIANAPOLIS • The yellow-green streaks of fireflies that bring a magical air to summer nights, inspire camp songs and often end up in jars in children's bedrooms may be flickering out in the nation's backyards as suburban sprawl encroaches on their habitats.

Scientists concerned by reports from the public that they are seeing fewer of the luminous insects each summer have turned to a network of backyard volunteers spanning much of the nation to track their range and numbers. Their observations may shed light on whether fireflies are indeed declining — a trend that could dwindle the targets of the childhood rite of passage of chasing fireflies.

As this weekend marks summer's unofficial end, the Firefly Watch volunteers' work is winding down now that the insects' annual light show is over in all but southern states.

Helen Mester of South Bend, Ind., is one of about 700 volunteers who entered observations this summer of firefly numbers, the color of their lights and flash patterns into the online database maintained by Firefly Watch, which is sponsored by the Boston Museum of Science.

Mester, 54, has counted fireflies for three years for the program from her living room window or her deck, watching the lights that lead males to females for mating.

She's now adept at identifying a common Midwestern firefly often called the Big Dipper firefly by the upside down "J'' light trail its males make as they flash by. She then watches for their female love interests to reply with two blinks from their perch on shrubs or trees.

"That's the female saying, 'OK, here I am — come over here.' You can see the hook and then a couple of flashes. They're kind of a lime green," Mester said.

About 200 firefly species found east of the Rocky Mountains produce, through a complex chemical reaction, lights ranging from yellow-green and yellow-amber to a pale blue. Light-producing fireflies aren't found west of the Rockies.

Each of the light-producing beetle species has its own unique signaling pattern to attract mates, some blinking, others flickering with their light never turning off.

Since the online Firefly Watch began in May 2008, about 5,100 people from 42 states have entered firefly data they collected in their yards, area parks and meadows, said Paul Fontaine, the Boston museum's vice president of education.

Fontaine said the museum is committed to operating the program and database for at least 10 years to provide a year-to-year snapshot of firefly distribution.

The program, which also has volunteers in Canada, Costa Rica, Ghana and India, asks participants to watch fireflies for at least 10 minutes each week. Scientists at Massachusetts' Fitchburg State University and Tufts University are helping with the project.

The information accumulating in the Firefly Watch database may help determine if fireflies are really declining, and if so, where it's happening and what could be causing it, said Christopher Cratsley, a biology professor at Fitchburg State College in Massachusetts who studies fireflies.

Cratsley said replacing meadows and fields with strip malls and parking lots clearly cut firefly numbers. And there's evidence that the glare of streetlights that come with urban sprawl may interfere with the courtship of some firefly species by outshining their flashes.