WELCOME TO THE BOARDS, TIGGS!!!
Don't feed your VFT moths. They are poisonous to VFTs!
The reason the VFT did not eat the bug:
Well, it goes a little something like this, If the bug is alive, It will land on the VFT's trap, triggering the trigger hairs and the trap shuts.
The bug wiggles around, trieng to escape, and therefore triggers the hairs still more, at this time, the VFT knows it has something that is alive and it closes fully and starts to digest the meal. It can take up to two weeks for the VFT to get done digesting the bug and open again.
However, If the bug is dead:
You drop the bug into the trap and trigger the hairs and it shuts.
Since the bug obviously isn't alive, it doesn't wiggle and try to escape. Therefore it doesn't trigger the hairs, the VFT then figures it's prey got away, so it opens back up.