How do fireflies synchronize their flashing?

The answer

Synchronous fireflies (Photinus carolinus) in the Great Smoky Mountains and several Southeast Asian species flash in near-perfect unison across thousands of individuals, creating a mesmerizing display. Each firefly has an internal oscillator, a biological clock that controls its flash timing. When fireflies observe their neighbors' flashes, they adjust their own timing slightly to match, a process mathematically similar to coupled oscillators. Over minutes, this mutual adjustment causes the entire group to synchronize. The primary purpose of flashing is mate attraction: males flash species-specific patterns, and females respond with precisely timed answering flashes. Synchrony may benefit males by making their species-specific patterns clearer against background noise from other species, or may result from competitive male-male signaling.