As night fell Friday on Cylburn Arboretum and a loud, familiar chorus of trills welled up in the woods, Debby Tupper strained to identify different species of crickets she had just spent more than an hour learning about at a riveting lecture and slide show.
To Tupper, 60, a special education teacher for Baltimore County public schools, it still sounded like a wall of surround-sound.
"My ears are trying to sort it out. You can hear different layers, but trying to train on one takes practice," she said, chuckling.
Tupper is one of many Baltimore and Washington residents who are practicing this week for the region's first-ever Cricket Crawl, set for Aug. 24. People are asked to gather in parks and back yards, to spend at least one minute cocking an ear for the mating and defense "songs" of eight distinct varieties of crickets and katydids. Cricket Crawl events will be held at Cylburn and Robert E. Lee Park among other locations, starting around 8 p.m.
Once participants think they've correctly identified the species, they can call, email, text or Twitter their auditory observations into the U.S. Geological Survey, which will create an online cricket locator map, in real time, based on the anecdotal data.
More of a species survey than an actual cricket count, the main goal of Cricket Crawl 2012 is to post the population distribution of the eight target species online.
"It's not a count. It's, 'What are you hearing and where are you?'" said Linda Davis, an organizer of the Cricket Crawl and member of the Overlea-based Natural History Society of Maryland, co-sponsor of the event along with the Geological Survey, the Audubon Naturalist Society and discoverlife.org.
But there is another goal.
"We're trying to get people connected to the nature where they live," Davis said.
Tupper, a Maxalea resident, was one of about 40 residents from as far away as Ellicott City who packed a classroom at Cylburn's greenhouses Friday for a talk by a noted cricket expert, as a run-up to the Crawl. The talk was followed by a short walk around the parking lot, so that people could listen to cricket calls.
The singing of crickets and other insects can be traced back to 360 million years from fossils, said lecturer Wil Hershberger, of Hedgesville, W. Va. He and Lang Elliott co-authored a 2007 book called "The Songs of Insects," which was published by Houghton Mifflin and is in its third printing.
"This is the first song of the planet, the song of insects," said Hershberger, 53, a naturalist, writer, nature photographer and a recorder of natural sounds.
Using slides with audio files, Hershberger enthralled his audience with synopses of the eight target species — the Northern fall field cricket, jumping bush cricket and Japanese burrowing cricket, as well five species of katydids, the greater and lesser anglewings, oblong-winged, fork-tailed, and the common true katydid.
Only the males sing, rubbing their wings together like a file against a scraper, Hershberger said. The pitch and duration of their chirps vary from species to species, from the common virtuoso katydid, with a chirp so high-pitched that it's hard to hear, to the robust conehead katydid, the loudest of the bunch.
"Lang says it drills a hole in his head," Hershberger told the audience.
And like thermometers of nature, they sing only in warm weather and not in the rain. In fact, if you count how many times a cricket chirps in 13 seconds and add 40 to the number, you get the day's temperature, Hershberger said. He said cicadas only sing when it's 72 degrees.
He described the different, often mathematically precise series of chirps unique to each species, like the short-winged katydid's "chirp, chirp, chirrrrp," or the "diagnostic" chirp of the greater anglewood cricket, which looks like a leaf and sounds like "something out of Star Trek," he said.
He even mimicked the various chirps with uncanny accuracy.
The Northern fall field is the quintessential cricket, he said, the one that "gets under the refrigerator and sings all night long, much to our chagrin."
But the fall field is in danger of being displaced by the Japanese burrowing cricket, its chirp at least twice as fast, which was introduced in Washington in 1959 and has spread fast, Hershberger said.
The silvery jumping bush cricket inhabits boxwoods and is known for its short trills, whereas the broad-winged tree cricket shows off its beautiful, continuous trill, Hershberger said.
Some songs are too loud even for the singer. The scissor-grinder cicada, for example, covers its ear with a muscle as it sings, he said.
Though it rained during Hershberger's presentation, the rain stopped before he led participants on a walk to hear crickets sing — and they were right back at it after the shower. Using two different flashlights, he was able to pinpoint the sound of several cricket species ("There are probably 20 different ones right here in the parking lot," he said) and then illuminated the insects for the walkers.
Most likely to be seen in north Baltimore, he said, are the greater and lesser anglewing and common true katydids, the jumping bush cricket and the Northern fall field cricket.
"This is the lesser anglewing," he said in the darkness, sorting through a cacaphony of thousands of bugs to spotlight one in particular.
Many of the people who attended the talk were casual nature lovers, there out of curiosity. Filmmaker Amy Genevieve Kozak, 35, of Waverly, said she learned of the talk while attending a jazz concert at the arboretum.
Banker Marc Horwitz, 65, of Pikesville, and his wife, Harriet, said they are are big fans of the arboretum, where their daughter, Carrie, now grown, climbed a tree at the top of the hill as a child.
Even John Schaeffer, 59, a biologist from Ellicott City, said he found out a lot that he didn't know.
And he added, "I've found out more about my hearing."
How to do a cricket crawl
Walk around in the outside location of your choice — like a local park or your backyard —on Aug. 24 with family and friends between 8:15 p.m. and midnight, and listen for one minute to identify one of the eight target species of crickets and katydids. You can learn the various calls at http://tinyurl.com/7y5trym. No need to count; just write down which species you hear.
Send in your results as soon as possible by calling 707-820-7732 and leaving a voice message, or texting the same number. You can also email your results,with photos and sound files if you want, to the website firstname.lastname@example.org, or twet results to @DevDemoHi.
Include your name, the specific location where you listened with the address or nearest intersection, a list of the species you detected, the time you started listening, and an anecdote or observation that you think other participants would like to know about.
Visit the website www.hawaiiwetlands.org:8080 to follow along as the data is mapped in real time.