Where have the fireflies gone in southwestern Pennsylvania?

Hot and dry weather during most of July has dimmed the light spectacle of fireflies in some urban and other parched landscapes, according to some local experts.

Naturalists from the Pittsburgh Parks Conservancy report less of a good showing this year of the beetle of summer — the firefly — with its erratic blinks of luminescent yellow light shone during their aerial courtship romps in backyards and field edges.

“Last year I saw tons of lightning bugs,” said Mike Cornell, a naturalist with the Pittsburgh Parks Conservancy. “I’ve seen a bunch so far, but not like last year,” he said. After conferring with other Parks Conservancy naturalists, they note they are seeing fewer fireflies this year, but are reporting a good number of them at parks and cemeteries.

The sprightly insect is still providing its ritual summer light show along fields, yards and moist meadows in the Laurel Highlands, said John Wenzel, an entomologist and director of the Powdermill Nature Reserve, Carnegie Museum of Natural History, in Rector.

However, the abundance of fireflies seems spotty in some areas this year and that could be blamed on not-so-Pittsburgh weather this summer.

“The hot dry weather of past two weeks has been detrimental as they like humidity,” Wenzel said.

The weather has been anything but, said David Shallenberger, a meteorologist with the National Weather Service in Moon.

For July and the summer so far, the Pittsburgh region has been down about one-third of its normal rainfall, Shallenberger said. The dew point, a measure of humidity, has been below normal for July in the region as well, he added.

“We’ve had an uncommon dry stretch and the sixth longest heat wave on record from July 3 to 10,” Shallenberger said.

Fireflies like warm humid nights with still air, Wenzel said. “If they don’t get that, they will wait weeks (to resume their courtship flights).”

During the summer, the asphalt in populated areas can be hot and dry. Pittsburgh parks such as Frick, Riverview and Schenley are “cool islands in the city that are sanctuaries for wildlife,” Cornell said.

There’s no doubt that fireflies are still out there, but it’s a matter of where.

Deaglan McManus, a park ranger for Allegheny County Parks, counted at least 21 fireflies within 10 seconds in a meadow in Harrison Hills park in Harrison on July 11 for the Firefly Watch Citizen Science Project, sponsored by the Massachusetts Audubon Society and Tufts University.

“I have not seen a change,” McManus said. “I see them in small patches of grass in my neighborhood, but with the dryness, it can delay their season.”

McManus advises the public if want to see fireflies to visit North Park and South Park where he has seen a good number of them. Those two parks are the only county parks open after sunset until midnight, he noted.

Habitat plays a role in the number of fireflies. Expect a lot of fireflies in a healthy and natural aquatic ecosystem, Wenzel said. “The Amish farms are famous for fireflies,” he noted. “They don’t farm the edge of creek banks and don’t use insecticides.”

Cornell added that fireflies can live in grass and lawns and if pesticides are applied, they are less likely to be seen in suburban and urban neighborhoods.

Recent research has pointed to the role of insecticides and habitat loss as causing firefly populations to decline worldwide.

Researchers blame development and light pollution, according to the website firefly.org.

Habitat loss looms large as most species of fireflies “thrive as larvae in rotting wood and forest litter at the margins of ponds and streams,” according to the website“And as they grow, they more or less stay where they were born. Some species are more aquatic than others, and a few are found in more arid areas—but most are found in fields, forests and marshes.”

Mary Ann Thomas is a Tribune-Review staff writer. You can contact Mary at 724-226-4691, mthomas@triblive.com or via Twitter .