Tiny lightning bugs that blink in unison are becoming such an attraction at Congaree National Park that crowds are threatening to overwhelm the nature preserve southeast of Columbia.

That’s the concern of some visitors who said they left the park in frustration last year after encountering traffic snarls, overzealous gawkers and a lack of park staff to manage the crowds.

“There was nowhere to park in the parking lot and there was nobody directing traffic; it was a total mess,’’ Irmo resident Dick Sharpe said. “Then, once you got into the park, people were tramping through the woods, they had flashlights out and they were trying to take flash pictures of the fireflies. It ruined the experience.’’

Aware of the complaints, National Park Service officials are beefing up staffing to control traffic and large crowds attracted by the synchronized flashing of fireflies between now and early June. The National Park Service in the past has not typically kept personnel on duty at Congaree National during the annual nighttime firefly spectacle.

“We are going to have staff here later,’’ said park ranger Jon Manchester, “so that we can better manage some of the flow going through. This has been getting bigger and bigger and bigger every year. We’ll see where we go this year.’’

Starting Saturday, rangers will be on duty during the evening, and the visitors center will remain open until 9 p.m. The fireflies begin to blink just after the sun goes down, which now is about 8:20 p.m. The best time to see the lightning bugs is from about 9 p.m. to 10 p.m.

Folks pour into the park this time of year to see the firefly display, making it the busiest time at Congaree, according to one recent park email. Congaree National Park, a 27,000-acre floodplain preserve, is one of the most easily accessible places in the country to view the flashing bugs.

For several weeks, usually beginning in mid-to-late May, fireflies light up at the same time, rather than blinking intermittently as they do other times of the year. Some people say the blinking looks like Christmas lights, except the fireflies flash in unison.

The phenomenon, believed to be part of a spring mating ritual, also can be seen at the Great Smoky Mountains National Park in Tennessee, a wildlife management area in Tennessee and at the Allegheny National Forest in Pennsylvania.

But crowds in the Smokies have gotten so large that the National Park Service limits the number of people allowed to view the lightning bugs. Great Smoky Mountains National Park received more than 18,000 applications for access to see the fireflies this year, but will issue only about 2,000 passes, said the park’s Jamie Sanders. Sanders said limiting access protects the bugs.

“Having people walk around and trample the vegetation would just kill the population,’’ Sanders said.

Manchester said Congaree National Park has no plans to limit access, but park officials will start counting visitors to learn how many people actually are showing up.

Park staff will help with traffic this year, but one of the main services will be to provide guidance. Park rangers and volunteers, for instance, can tell visitors the best ways to view fireflies – as well as what not to do. Nature sometimes is such an attraction that crowds can detract from the experience if they are not careful, Manchester said.

“We are definitely trying to help people understand that too much going on can be just as damaging to the resource as people not caring enough,’’ he said.

Park officials will discourage the use of bright flashlights that can block out the synchronized blinking. People also will be encouraged not to catch fireflies in jars and to stay on the boardwalk or walking trails. One of the best spots is easy to reach: just beyond the visitors’ center on the Congaree National Park boardwalk.

That all sounds good to Sharpe, who said seeing the fireflies is a great experience if others are considerate and the park is properly staffed.

“These things are amazing,’’ said Sharpe, a former state air quality regulator who is married to a park volunteer. “We see fireflies in the backyard, but they are random. To see everything flashing on and off at one time is really a fantastic natural thing.’’