Only in the sequels a full moon, but in this film it's the Autumn moon as said in the poem.
In The Howling a werewolf can change at will, in Wolf Jack Nicholson change at a quarter moon, in Bad Moon can change at any moon.
Yes, it seems the "rules" for vampires and werewolves change in just about every story. It sort of depends on how the author wants them to be.
Death lives in the Vault of Horror!
I think what they would mean by the Autumn moon in the poem, is the full moon in October. The full moon in that month is also known as the hunter's moon. I believe that in all of the other Universal movies in which the wolf man appears, it is any time that the moon is full. When Universal made 'Abbott and Costello Meet Frankenstein,' they definitely have the wolf man complaining that he turns into a wolf every full moon.
shareIn the sequels, the change always happened when the moon was full.
On the 1987-88 show Werewolf, they specifically say that the full moon is NOT what triggers the change. It's very random and can occur on any given night. The only warning is that the pentagram appears on the werewolf's hand the day before the change happens and get progressively more visible as the change draws nearer.
The pentagram suddenly appearing on the werewolf's hand as a warning of the change, as you described, is a better way of signalling an impending transformation. I will try to catch up with that 1987-88 show. It sounds good. I like the way that the pentagram as a warning is used in 'The Wolf Man.' Appearing in the hand of the werewolf's next victim. I can't forget the look of dread in Bela Lugosi's face when he sees it, when he is about to read that lady's fortune.
shareAutumn as in Hunter's moon interesting.
And there's the part about the wolfbane blooms.