I have witnessed this in Western North Carolina! It was one of the most unique and beautiful experiences of my life. Everyone I've told this to has thought I was crazy, dreaming, or high, so it's good to know that it wasn't just my imagination!
Can you provide some kind of a resource for me to read? I want to learn more!
It was about 10 pm, and there were millions of fireflies in the woods. When they flashed, it was like a wave of light propagating all around. Amazing.
I'm supremely jealous. It must be beautiful. I'm actually entertaining the idea of building something using light bulbs to simulate this, but alas...
As to information, I don't have much. Mathematically it's simply a case of a system of coupled oscillators: the fireflies merely mimic the frequency of their neighbors' flashes until they're all flashing at the same time. My understanding is that the biologists haven't exactly figured out how fireflies have this sort of internal clock that causes them to do this.
I first learned about it in KK Tung
Topics in Mathematical Modeling. I'll just quote the small passage he devotes to the topic:
Philip Laurent wrote in Science in 1917 about a phenomenon he saw in Southeast Asia: "Some twenty years ago I saw, or thought I saw, a synchronal or simultaneous flashing of fireflies. I could hardly believe with my eyes, for such a thing to occur among insects is certainly contrary to all natural laws."
Joy Adamson wrote in 1961 about an African version of the same phenomenon: "A great belt of light, some ten feet wide, formed by thousands upon thousands of fireflies whose green phosphorescence bridges the shoulder-high grass... One is left wondering what means of communication they possess which enables them to coordinate their shining as though controlled by a mechanical device."
It is the males that flash to attract females. Individual males have their own light-emitting oscillators, with a natural period of about 0.9 second, but also have some ability to change the period to mimic the flashing of a particularly strong neighbor, thus increasing their own attractiveness to the females. Some species of fireflies can do this better than others, being able to change their frequency of their flashing by up to 15% in response to an external stimulus.
And the rest goes into the technical aspects of how this is mathematically feasible.
I managed to find this article on the topic:
Flash Precision at the Start of Synchrony in Photuris frontalis1 | Integrative and Comparative Biology | Find Articles at BNET.com
If you're interested in more (from a mathematician's prospective) I'd recommend the book
Sync by Steven H. Strogatz, which is a very friendly book that covers lots of other examples of "spontaneous synchronization" in nature. If you're familiar with mathematics up to differential equations, you might try Strogatz's other text
Nonlinear Dynamics and Chaos for a more technical treatment.
I don't really know any references from biologists. I could look Tung's references up though and see where he got his info.
Also, here's a cool simulation someone wrote using a computer:
http://ccl.northwestern.edu/cm/models/firefly/firefly1.mov
