Creatures reminding us that conflagration moves fast (9)
I believe the answer is:
Here is my best explanation:
'creatures reminding us that' is the definition.
'fireflies' can be an answer for 'creatures' (firefly is a kind of creature). I am not sure about the rest of the definition.
'conflagration moves fast' is the subsidiary indication.
'conflagration' becomes 'fire' (I've seen this before).
'moves fast' becomes 'flies' (flying is a kind of moving. I am not sure about the 'fast' bit.**).