In this new series, we’re gonna be looking at some of the folklore and history behind some of the Wesen, gangs and other monsters of Grimm.
This week we’re gonna be looking at the Rat King, and as David Giuntoli said ‘Don’t Google images of real life rat kings.’ Below the cut is talk of animal injury and animal death.
There is a lot of superstition surrounding the rat kings and why or how they are made, or even operate. It’s long asserted that they are purely mythical, but a living one of squirrels was found in 2013. They were melded together by the sap from the tree they lived on, and moved as one giant animal instead of several squirrels tied together. Apparently this is not uncommon. The picture through the link is of them being untied.
So what is a rat king? It’s, nominally, a group of rats tied together at the tails. The creepy thing is, instead of moving as seven (or 16, or 32 depending on which story you’re reading) rats/mice/squirrels, it appears to move as one monstrous creature.
The appearance of a rat king is a bad omen, probably due to the connection between rats and the plague.
It is said that rat kings appear naturally, like the squirrel king above, but evidence shows them sometimes being tied together with things like horsehair, which doesn’t appear in rat nests.
Terry Pratchett comes up with the most logical idea in The Amazing Maurice and His Educated Rodents – “down the ages some cruel and inventive people have had altogether too much time on their hands".

Yeah, they don’t look like that. In fact, it’s worse.
Further Reading:
The Amazing Maurice and His Educated Rodents by Terry Pratchett, which was one of my most favourite books as a kid. Featuring talking rats, cats and dastardly plans, it’s actually one of Pratchett’s scarier books, especially of his children’s books.