A massive swarm of fireflies is set to light up the Great Smoky Mountains. However, due to the coronavirus, viewing events have been canceled. Every year in late May or early June, thousands of visitors from across the country gather near the popular Elkmont Campground to observe the naturally occurring phenomenon. But not in 2020. Officials with the National Park announced the annual viewing has been canceled to slow the spread of the novel coronavirus. “The synchronous firefly viewing area at Elkmont simply isn’t spacious enough to safely allow hundreds of people to gather under the current health guidance,” park officials said. “While disappointing, the safety of our employees, volunteers, and visitors continues to be our number one priority.”Park officials also noted that the shuttle service to the event would not support current CDC guidelines, particularly the 6-feet distancing requirement between individuals. Due to on-site parking limitations, the shuttle service is the only transportation mode for visitor access during this period, except for registered campers staying at the Elkmont.Synchronous fireflies are one of at least 19 species of fireflies that live in Great Smoky Mountains National Park. It is the only species in America whose individuals can synchronize their flashing light patterns.Their light patterns are part of their mating display.Each species of firefly has a characteristic flash pattern that helps its male and female individuals recognize each other. Most species produce a greenish-yellow light; one species has a bluish light. The males fly and flash and the usually stationary females respond with a flash.Peak flashing for synchronous fireflies in the park is normally within a two-week period in late May to mid-June.No one is sure why these fireflies flash synchronously. Competition between males may be one reason, park officials say: they all want to be the first to flash. Or perhaps if the males all flash together they have a better chance of being noticed, and the females can make better comparisons.The fireflies do not always flash in unison. They may flash in waves across hillsides, and at other times will flash randomly.Synchrony occurs in short bursts that end with abrupt periods of darkness.The mating season lasts for approximately two weeks each year. The dates that the fireflies begin to display varies from year to year. Scientists haven't figured out why, but it depends at least in part on temperature and soil moisture. It's impossible to predict in advance exactly when the insects will begin flashing each year.