Magic cicadas, insects that emerge in great, noisy numbers only once every 17 years, are showing up on the East Coast now—but they are not expected to make an appearance on Long Island after all.

That’s good or bad news, depending on your point of view. Some people time their weddings to avoid them. Others celebrate the insects’ emergence with musical duets or cicada cook-offs.

There are different groups of magic cicadas, also called periodical or 17-year cicadas, that emerge in different cycles in different places. The one turning heads now on the East Coast is Brood II, which was last seen in 1996. Juveniles from the eggs laid by adult cicadas that year have been living underground ever since, feeding on tree roots and working through various stages of development. Now they’re emerging to mate and lay their own eggs, whose larvae will hatch this summer and then burrow underground, not to be seen again until 2030.

“It’s quite a fantastic natural phenomenon,” said Jim Ash of East Hampton, former executive director of the South Fork Natural History Museum in Bridgehampton.

“Millions of them come out at once,” said Eric Salzman of East Quogue, who writes a nature blog called “The View From Weesuck Creek.”

“It’s like New Year’s when the ball comes down,” said Larry Penny of Noyac, the former natural resources director for East Hampton Town.

Yet Mr. Ash said he’d seen any number of news programs that made it sound as if the cicadas’ arrival would be “like Armageddon.”

During a really big emergence, people shut their windows to block out the sound, said Mr. Penny, who described it as “like helicopters going over.” Mr. Salzman described the noise as “a massive buzzing, blooming cicada symphony.”

The symphony comes from the males, who flex a drum-like membrane on their abdomen to make females take note, according to Daniel Gilrein, an entomologist with Cornell Cooperative Extension of Suffolk County. There is a good reason periodical cicadas surface in extremely large numbers: it’s to surprise and foil predators like birds and raccoons, who simply can’t eat them all.

The cicadas lay their eggs in twigs, which can damage young, unprotected trees, but usually do not cause other problems despite their numbers. “You might note that they are very gentle creatures, not harmful to humans in any way, and easily caught,” Mr. Gilrein said in an email.

Mr. Gilrein said he did not expect to see periodical cicadas on Long Island this year, although there were already reports of them appearing in Rockland County upstate. He recalled a Brood XIV emergence in 2008 with cicada sightings in Riverhead, and said a more scattered emergence of Brood V is expected in 2016.

“It’s a curious thing that it’s a false alarm,” Mr. Salzman said. “Everyone just assumed that if [they] were in the city they would have to be out here as well.”

A website called www.cicadamania.com includes a wedding planner to avoid scheduling conflicts in late May and June when cicadas are expected to emerge, as well a wealth of cicada lore—for instance, that they are attracted to the sound of power tools and lawn mowers, and in some places are eaten on kabobs and in gumbos and creole.

“You’ll undoubtedly hear of some ‘cook-offs’ using cicadas this year,” said Mr. Gilrein. “I have not partaken, but reports are they can be quite good, especially the teneral (newly emerged) adults, before the exoskeleton hardens off.”

Periodical cicadas are not to be confused with annual cicadas, a different species that arrives later in summer, or with locusts, which they are not.

Possibly Bob Dylan made this mistake when he wrote “Day of the Locusts,” said to have been inspired by a 1970 commencement at Princeton that he did not want to attend, and where there was an infestation of cicadas.

On the subject of music, a friend of Mr. Salzman, David Rothenberg, was scheduled to perform a duet with the insects at the South Fork Natural History Museum on May 25—but he had to improvise, as there were none to be found.

However, Carol Crasson, the museum’s education and communications director, did point out that Dr. Elias Bonaros, a cardiologist and amateur entomologist, will present “The Buzz About Cicadas” at the museum on August 10, offering updates on the progress of Brood II, as well as a few live specimens for a look and a listen.