Magicicada septendecim, the biggest and most common of the three, sounds like a giant Weed-whacker or sci-fi spaceship. Magicicada cassini produces a "tick, tick, tick ... zzzzzt" sound in quieter moments. When it's not -- the norm -- it makes a harsh screeching noise like the sound of a "million baby rattles," says Williams. "They're the loudest."

The third species, Magicicada septendecula, also produces a ticking noise but is the rarest of the three and much harder to distinguish, Williams says.

The ash trees were filled with Magicicada septendecim and Magicicada cassini, Williams said. Pagac held the decibel meter in the air. Its digital readout quickly started to climb.

87.2 ... 89.4 ... 89.9

"How high can we go?" hollered Williams, wearing a tie-dye yellow T-shirt with the image of Magicicada septendecim on the front.

The meter topped out at 90.3 decibels-- slightly louder than a lawnmower. Last weekend, Williams said, she found a tree that measured 92 decibels.

Cacophony is 'cool'

"It made the hair stand up on the back of my neck. It's cool," she said.

Not everybody is finding the high-decibel dirges so cool, however.

At the Baltimore Zoo, employees have been forced to shout in the thickly wooded areas and listen hard for the sound of their walkie-talkies.

"Do you realize maintenance is trying to get you on the radio?" a panting keeper told zoo employee Ben Gross yesterday after catching up to him on the the cicada-infested African boardwalk.

In Lauraville, musician Gavin Elder can hear the bugs between songs in the basement recording studio at his home even with the window shut. He has been thinking about giving them a part on his coming psychedelic surf album.

"They have a really great other-worldly drone," he said. The liner notes, he imagines, could read "backing vocals by Brood X."

Elder's wife, Traci, said the cicadas are so loud they drown out the phone, causing them to miss three calls last weekend.

But the couple said that in some ways they'll miss the creatures when they're dead in a few weeks -- their songs mask the more annoying sound of traffic on nearby Harford Road.

The cicadas should consider themselves lucky they're bugs.

In some areas, the Maryland Occupational Safety and Health Administration could cite them for exceeding the 85- to 90-decibel limit set by law, according to spokeswoman Linda Sherman.

Regulators at the city Health Department's environmental health section would crack down, too. Daytime noise limits are set at 58 decibels at the property line in residential areas. Power tools and air-conditioning equipment are not allowed to exceed 70 decibels during the daytime in the city's neighborhoods.

None of the agencies said they planned any enforcement action, however.

Sun staff writers Julie Bell, Jonathan Bor and Frank D. Roylance contributed to this article.