How to shoot fireflies?

I've come to the conclusion that taking long exposures of fireflies firing off on the lawn is the hardest photography assignment there is.
The subject:

• Comes out in very low light, that gets lower fast. So the exposure is changing minute by minute.

• The subject is very small. Macro.

• The subject flies around in random patterns and is invisible to the human eye until

• It lights up, but just for second.

• They tend to cluster in groups but the groups shifts position constantly.

• The bio-luminescent light is so minimal, it is hard to pick up on film or sensor.

I think it might be possible to shoot clusters of fireflies in a controlled environment but, that is different from a grassy suburban lawn in summer!