Why doesn't the Marauder's Map account for any transformed animagi's adopted name?

And, how does the Marauder's Map register the names of people in the first place?

  • 13
    I think this is a common programming mistake. Sure the compiler does implicit casting correctly most of the time, but what we're seeing here is someone has an empty try-catch block that catches the cast, and then displays no warnings or errors on the user interface (it is a piece of parchment after all, it may have no facility for such errors). You see this with programming languages where syntactical form is so peculiar and non-programmer friendly (Expelliarmus? Really? And there's no IDE to do pronunciation correction for you either!).
    – John O
    Commented Mar 29, 2013 at 16:27
  • possible duplicate of What Kind of Magic Was Used to Create the Marauder's Map? Commented Mar 29, 2013 at 19:38
  • @JohnO - levi-oh-sah, not levi-o-ser...
    – HorusKol
    Commented Jun 10, 2016 at 14:37
  • @JohnO: This may also simply be a matter of the objects having a custom Name property (which changes to the animagus' adopted name), whereas the Marauder's Map is implicitly relying on an overriden ToString() method (which does not change based on the animagus' adopted name, hence the bug)
    – Flater
    Commented Aug 1, 2017 at 13:51

5 Answers 5


As mentioned on this link the Marauder's map works as follows:

The Marauder's Map is a magical document that reveals all of Hogwarts School of Witchcraft and Wizardry. Not only does it show every classroom, every hallway, and every corner of the castle, but it also shows every inch of the grounds, as well as all the secret passages that are hidden within its walls and the location of every person in the grounds, portrayed by a dot. It is also capable of accurately identifying each person, and is not fooled by animagi, polyjuice potions, or invisibility cloaks; even the Hogwarts ghosts are not exempted from this.

Further down you can see that :

Similarly, it identifies animagi by their actual name even when they are in their transformed state. It was by this mechanism that Lupin was able to identify Peter Pettigrew's presence at Hogwarts despite being presumed dead.

Though its not mentioned anywhere how the Marauder's Map registers the names of people, I think it is quite elementary magic to divine name of the people in the world of Harry Potter where you can even remain as a ghost in the world. :)

  • 1
    :D i like this answer Commented Mar 29, 2013 at 11:23
  • 4
    Is there a canon reason explained for the second Wikia quote? It sounds like someone was merely describing things in a book. E.g. the book says "Peter" was on the map instead of "Scabbers", and Wikia writer extrapolated that into a big paragraph. Yet, you are using that paragraph to answer and explain "why DID the map show Peter instead of Scabbers" - which is circular reasoning. Commented Mar 30, 2013 at 3:10

Purely speculation here, but I guess that it dealt with a person's given name. Names have power, and there are probably other spells as well which deal with a given name. A person's identity may be tied deeply with their given name.

As for your second question -- It's magic. If a person's identity is tied to their given name, then I guess that there must be spells which can find out a person's name.

  • "Names have power" - is there any evidence of that in Potter universe (as opposed to EarthSea)? Commented Mar 30, 2013 at 3:11
  • @DVK: Nah, it's a general trend found in many other fantasy worlds. Commented Mar 30, 2013 at 6:45

I don't believe Peter has ever adopted the name Scrabbers. His friends called him Wormtail. It's only the Weasleys, probably Percy Weasley, that have named him Scrabbers, and Peter didn't have the opportunity to tell his real name to them.

  • ok,then why not wormtail? Commented Mar 29, 2013 at 10:07
  • 1
    @THISISSPAAARRRTTTTAAA Wormtail was a nickname, not his given name, and only a few people reffered to him by that name.
    – Monty129
    Commented Mar 29, 2013 at 11:01

Perhaps as one of the original crew Wormtail was able to do a quick little spell that hid him from the average user, but as admin Lupin was able to see the whole thing?

Pretty proud of myself for coming up with that just now actually.


The Marauders Map uses the Homonculous Charm to keep track of every person in the surrounding area. The charm covered “the caretaker’s cat, Mrs Norris”. It did not distinguish between Barty Crouch Senior and Junior, and Harry did not find out the real name of Peeves the Poltergeist. Importantly, the map knows to use the Animagus names of Lupin, Black, Pettigrew and James Potter.

So the names are not taken from an official register. A cat’s name is unregistered and Pettigrew was believed to be dead. So, the map appears to be taking what people are called by.

So how to distinguish between “Mrs Norris” and say, an ordinary mouse. Well, as the mouse has no name, it’s not put on the map. That would save putting every living creature on the map. Most animals don’t have a name.

This explanation could also solve the alleged plot hole: Why did Fred and George not see that Peter Pettigrew was next to their younger brother all the time. The answer could be that the map displayed “Scabbers”, what he was called, until Sirius Black escaped into the Forbidden Forest, and started calling Scabbers by his real name with sufficient determination, that map then adjusted.

  • 1
    You seem to be answering the wrong question. The map reported Peter Pettigrew as “Peter Pettigrew”, and you're explaining why it reported him as “Scabbers”. Commented May 5, 2017 at 21:21

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