Bryn Mawr School officials are taking to heart a warning from a former headmistress about the possible perils of holding graduation outdoors next spring on the wooded, 26-acre North Baltimore campus.

The warning came in a June 1970 letter found this year in school files and written by Diane Howell. In her letter - addressed: "To Whom It May Concern in June 1987" - Howell described how a month earlier the "creatures emerged in earnest" just days before graduation, making an outdoor ceremony impossible because of the din.

The creatures in question were cicadas, irksome insects that emerge from the ground every 17 years to mate and lay their eggs, and in doing so, wreak havoc on trees and shrubs and make an incessant, high-pitched noise that drowns out nearly every other sound - including graduation speakers.

The cicadas are scheduled to make their next appearance in Maryland in the spring. And that's raised concerns among administrators at Bryn Mawr and other private schools in the Baltimore area, who are thinking about where to hold graduation next year.

In 1987, Bryn Mawr administrators heeded Howell's advice and moved the ceremony into the KVB gymnasium. And next year?

"We don't move from that garden lightly," said Nancy Sherman, director of communications at Bryn Mawr. "It would be an extraordinary compromise to hold it indoors."

The school has to decide soon. If graduation is not held outdoors, it may have to be moved off campus.

But if the school decides to follow tradition and award diplomas June 8 in the Gordon Garden, the Class of 2004 will be competing with millions of cacophonous cicadas.

Other private schools are delaying a decision because they have larger indoor facilities that can handle the ceremony.

In 1987, graduation at Boys' Latin in North Baltimore also was moved inside because of the cicadas, said Leslie Heubeck, the school's director of public relations.

Since the insects last appeared, several major construction projects have been completed at Boys' Latin. Because so much ground has been disturbed, the school may be forced to deal with fewer insects next spring.

"We have the luxury of waiting because our Gelston Athletic Center is large enough to accommodate our commencement," Heubeck said.

Unique to East Coast

The insects have long been called locusts, but they are periodical cicadas, said Gaye Williams, an entomologist with the state Department of Agriculture. After they crawl out of the ground, they fly to nearby trees and bushes where the males start a droning mating song that lasts from dawn to dusk and the females deposit eggs.

"The cicadas are unique to the East Coast," she said. "They like the old Eastern deciduous trees," including oak, maple, hickory, apple and various nut trees, but generally steer away from evergreens.

Williams stressed that the insects are not harmful, but they are very loud.

Mary Brady agrees. The retired archivist and teacher at St. Paul's School for Girls in Brooklandville said the cicadas make a "dreadful racket when they sing at the top of their lungs." She described the noise as a high-pitched, abrasive, metallic sound.

She isn't afraid of cicadas, but said they do spook a lot of people.

"They look like ghosts because they are milky white when they first emerge and then darken when they cling to the trees," she said.

The adult cicadas probably would be considered ugly, about 1 1/2 inches to 2 inches long with a black body, red eyes and legs.

Brady remembers the St. Paul's outdoor graduation in 1987 - the last time the 17-year cicadas appeared in the Baltimore area.

"It's fortunate that we had the outdoor graduation at all," she said. "It was a nuisance. The girls were squeamish, but they didn't squeal when the cicadas flew by or landed on their white dresses. We had more trouble with some of the parents.

"It wasn't very comfortable, but we did manage," she said.

'How awful that was'

Charlotte Douglas was one of the parents attending graduation in 1987 at St. Paul's. Now the school's director of admissions, Douglas said she wanted to see the graduation traditions continue.

"I remember a gentleman sitting in front of me with a cicada on his neck during the graduation," she said. "I left it there because I was afraid it would land in our row. I'll never forget how awful that was."

Howell, headmistress at Bryn Mawr from 1962 to 1973 who died this year, said in her letter that "survivors" of the 1953 outdoor graduation described the situation as "impossible: locusts crawled up legs, flew down dress necks, and made such a din that the speakers could not be heard."

Williams, the entomologist, said the insects are just part of the environment. Their only enemies are humans and deforestation.

Although they only live for six to eight weeks, the timing of their arrival couldn't be worse. Williams suggested that anyone planning an outdoor event in May or June would be well advised to rent a tent - one with sides on it.