Scientific American published an article about how to make
artificial fireflies which sensed and synchronised to
the flashing of others, as they do in nature.

Obviously totally synchronous flashing could be done by wiring LEDs
together - what would be nice is a pseudo-random display where
you generally got interesting waves of light.

If you are lucky enough to live near fireflies, you could attract
these amorous insects. Remember to use _green_ LEDs -
flashing red LEDs could attract life forms wishing to mate, but
unpleasant specimens of one's own species! :-)