OK. I'll admit that the fireflies in a jar thing has been done already. The difference here will be that this version will be done entirely with an analog circuit.
For anyone without a lot of electrical knowledge, what that means is that you can do the firefly circuit without needing to buy a PIC micro controller or do any programing on your computer. This circuit can be put together entirely from parts available at Radio Shack for a reasonable amount of money.
The one or two I have built are being used in enclosed projects with a translucent lens. I'm using them as night lights. The one pictured below is built from an old Weston meeter. You could easily use the micro LEDs and finer wire to simulate free-flying fireflies. I used green and yellow LEDs, and arranged them so some are closer to the front than others. The effect is somewhat hypnotic and organic. like there is something really alive in there.
The primary difficulty in designing this was in finding a way to randomly flash the LEDs. Much of the project was based off the very good instructions found here:
The Decade counter chip (LED driver) can actually drive up to 8 LEDs. I kept it to 5 just to keep the size and complexity down.
The second difficulty was finding a simple way to get a fade-effect in the LEDs. After a long series of fruitless searches and overly complex ideas, I found a few posts suggesting the use of a large capacitor and resistor combination. I worked it in, and the results were good enough. It does require some experimenting, though, to get the effect to work to your taste.
1 lm555 timer chip
1 cd4026b combined counter and display driver IC
16v 47uf capacitor
2 - 10k resistors
Jumper wire, a few feet.
LEDs. used 5-6 here, but with some creativity you could add more.
5-6 large capacitors. I'm using 1500uf
5-6 resistors of varying values
5v to 9V DC power source of some kind. You can use 4 AA batteries as well. It's not that fussy. I would not go any stronger than 9V without a 7805 power regulator or something.
Housing of some kind