We could solve this using a daemon, but for the sake of demonstrating a feature of thedark we won't. In Initialise, write thedark.initial = GoMothGo; and add the routine:

[ GoMothGo;
   if (moth in player)
   {   remove moth;
      "As your eyes try to adjust, you feel a ticklish sensation
       and hear a tiny fluttering sound.";
   }
];