As most nighttime wanderers know, fireflies look pretty scattered. Though their ons and offs may mean something to each other, to us, they tend to look random, like a tiny light show gone haywire.

But for a few weeks each year, a group of fireflies at Great Smoky Mountains National Park does something a little different—they blink in sync.

As detailed on the NPS website, there are at least 19 species of firefly in the park. Only one, Photinus carolinus, is synchronous. Big groups of airborne males all flash at once, like programmed Christmas lights. The females then respond more faintly, from the ground. Visitors are spellbound by the strobing. “This takes seeing fireflies in your backyard to another level,” one, Chuck Steinfurth, told the Miami Herald.

The fireflies start up at different times depending on soil, temperature, and other factors known only to bugkind. This year, they got going around the turn of the month. Viewing events are scheduled through June 7th, though getting in this year might require an extremely powerful wish—the spectacle has become so popular that the park only issues parking passes through a lottery. If they let everyone in who wanted to come, the fireflies would likely get trampled, park spokeswoman Dana Soehn explained to WBIR.

As for why they do it—that’s still a mystery, the park says. It might be that the males race to flash first, and end up blinking at the same time. Or maybe they just like the attention.

Every day, we track down a fleeting wonder—something amazing that’s only happening right now. Have a tip for us? Tell us about it! Send your temporary miracles to [email protected].