The Rat King
A rat king is said to arise when a number of rats become intertwined at their tails and become stuck to each other with blood, dirt and excrements. Consequently, the animals grow together while joined at the tails. The majority of instances of rat kings have been reported in Germany.

The name
The name ‘rat king’ may come from the old superstition that an aged wise rat sat on the entangled tails of rats and was treated as royalty by the pack. Alternatively it could derive from an early belief that the entangled rats were one organism, a supreme rat with many bodies.

The Otago Museum’s rat king
This display features a family of Rattus rattus, discovered in the 1930s. They had fallen from their nest in the rafters of a shipping company shed, and were immediately followed to the floor by a parent who vigorously defended the young. After they were killed they were donated to the Otago Museum. The tails are entangled with horsehair, which was presumably used to build their original nest.

How is the rat king formed in nature?
No zoologist has been able to prove exactly how rat kings are formed in nature. It is possible that the tails become entangled when the rats huddle together facing outward for warmth and security, with urine and droppings from those in the upper circle falling onto the entwined mass of tails. According to this theory when the rats try to pull apart the tails are pulled tighter, and the knots strengthen, knitting the rats together. Other possibilities are that the tails might become entangled while the males are fighting for females, during mass grooming, in the nest shortly after birth or after the tails of a number of rats come into contact with some sticky substance. The rat king remains as much a mystery to scientists today as it was to medieval peasants.