October 21, 2026, 9:46 am | Read time: 5 minutes
A “rat king” refers to a cluster of rats whose tails are inextricably knotted together. While it sounds like a myth from dark times, it is a rare but real natural phenomenon. In the Middle Ages, finding a rat king was considered a bad omen and a harbinger of disease and plague. This wasn’t entirely unfounded, as many rats indicate poor hygiene. However, the rat king has nothing to do with witchcraft or the devil. PETBOOK editor and biologist Saskia Schneider explains how such a cluster forms and what the name means.
How Does a Rat King Form?
Rat kings almost exclusively form among black rats (Rattus rattus), which have particularly long, thin, and prehensile tails. In tight nests or burrows, the tails of several young rats may touch while crawling and climbing, reflexively entwining and–aided by moist or sticky substances like urine, feces, blood, or nesting material–sticking together. If an attempt to escape is made, the cluster tightens. The resulting knot is so tight that the animals can no longer separate from each other. 1
The phenomenon occurs most frequently in winter–possibly facilitated by the freezing together of wet tails. Some hypotheses, such as the idea that the rats intentionally knot themselves, are now considered disproven. Manipulations or arrangements made after death cannot be ruled out in individual cases.
Why Is It Called a “Rat King”?
The term “rat king” originates from the German-speaking world. It likely stems from the notion that a king rules in every group–even in the rat realm. In old depictions, this king sits on a throne made of rat tails, equipped with a crown and scepter. A particularly vivid image that has persisted in literature and pop culture to this day.
“Rat king” was originally also used metaphorically: Sometimes it referred to a particularly large rat that ruled over others, sometimes it served as an insult for greedy people. Only later did the term refer to the actual phenomenon of rats knotted together. 2
Myths and Beliefs Surrounding the Rat King
In the Middle Ages, finding a rat king was considered a bad omen–a harbinger of disease, death, and especially the plague. This belief is not entirely unfounded: A high rat density can be an indicator of poor hygienic conditions, which in turn increased the risk of epidemic diseases. The “rat king” was therefore viewed with suspicion and fear. In literature, it was demonized–as a multi-headed monster like in Julius Wolff’s “Pied Piper of Hamelin” or as a supernatural being carried by its subjects.
Can the Rats Survive?
Surprisingly, yes–at least for a certain time. There are documented cases of live rat kings, where individual animals even showed signs of being cared for by other rats. The affected animals cannot move, but they may feed on food scraps in the nest or grains trickling through the floor. 3
Nevertheless, a rat king is an evolutionary dilemma: The knotted animals are easy prey for predators and usually die from hunger, injuries, or infections. The fact that many rat kings have been found mummified, such as wedged in tight building structures, is explained by the dry environment and lack of decay.
Historical Evidence
The most famous and largest rat king was found in 1828 in Buchheim near Altenburg, Thuringia–a cluster of 32 black rats, mummified in a chimney. This specimen is still on display at the “Mauritianum” Natural History Museum in Altenburg. 4In total, about 50 to 60 finds are documented worldwide–most from Central Europe, particularly from Germany, France, the Baltic states, and Denmark. 5
Since the 20th century, rat kings have been found less frequently–presumably due to better hygiene, declining rat populations, and the displacement of the black rat by the more robust brown rat (Rattus norvegicus), whose shorter tail makes knotting less likely.
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The Phenomenon Also Occurs in Squirrels
Less known but no less astonishing is the comparable phenomenon of the so-called “squirrel king.” Here, the tails of young squirrels stick together–usually due to tree resin, nesting material, or human waste–into an inextricable knot. Unlike with rats, this condition is almost always discovered while the animals are still alive, such as when they fall from the nest together.
In North America and Canada, several such cases have been documented in recent decades, where the animals were successfully separated with human help. Without intervention, they would hardly have been viable.
Conclusion:
The rat king is a rare and fascinating natural phenomenon that has captivated scientists and laypeople alike for centuries. Its history lies between superstition, horror, and astonishing biology–and it reminds us of how surprising and curious nature can sometimes be. Whether as a warning signal for poor living conditions or as a biological curiosity, the rat king remains a phenomenon that captivates our imagination as much as it challenges our research.
About the Author
Dr. Saskia Schneider is a biologist with a Ph.D. During her studies at the Free University of Berlin, she focused primarily on zoology and animal behavior.