Lemurs. Some of them, like the tiny mouse lemur, are impossibly cute. Others, like sifaka and its extraordinary bounding walk, are impossibly hilarious. And at least one, the nocturnal aye-aye with its creepy elongated finger, is impossibly weird. But every single one of them is native to Madagascar and its surrounding islands—and together, every single one of them takes its name from one of Ancient Rome’s creepiest bits of folklore.

The name lemur derives from the Latin word lemures. Some dictionaries translate that word as simply meaning “ghosts,” but in Roman tradition there was a lot more to it than that definition would suggest.

The Lemures of Ancient Rome were in fact grotesque skeletal specters, who would wander the earth at night causing hurt and injury to the living. According to the early Christian scholar St. Augustine (who brought it up to disagree with it), these were the cruel and malevolent ghosts of iniquitous characters and lost souls: thieves and criminals, the executed and the damned, and all those who for whatever reason had not been afforded a proper funeral, like sailors lost at sea whose bodies could not be recovered and buried appropriately. According to Roman poet Ovid, they were “voiceless spirits” who would walk the earth in search of their old homes, terrifying all those who crossed their paths as they wandered the streets at night. The only way to hold them at bay, he explained, was to exorcise your home during an early springtime festival known as Lemuria. At midnight on the ninth, 11th, and 13th of May, the head of the household would walk the house barefoot, throwing a ceremonial offering of dried black beans over their shoulders with the words “with these beans I redeem me and mine.” Bronze pots and dishes would then be clashed together, creating a cacophony of noise meant to drive the spirits from the house. Only once this ritual had been completed for the third time would the house be deemed as safe for another year.

No one is entirely sure why the Romans knew these ghosts and demons as lemures, but the theory put forward by Ovid was that the first of all these beings was the ghost of Remus, the legendary co-founder of Rome who was killed by his twin brother Romulus after a bitter dispute over the founding of the city. The macabre festival of Lemuria, ultimately, was originally Remuria—a festival intended to commemorate Remus’s death and placate his spirit.

What does all that have to do with the bouncing sifaka and the creepy-fingered aye-aye? Well, for the next piece of the puzzle we need the Swedish botanist and taxonomist Carl Linnaeus.

One of the most acclaimed scientists of his day, Linnaeus was the father of the Linnaean system of classification, which divides all living creatures into an intricate hierarchy of kingdoms, genera, and species. He outlined this groundbreaking system in several editions of his Systema Naturae, most influentially in 1758, and it has remained in use (albeit with various extensions and modifications over the centuries) ever since.

Using this system, Linnaeus entered a record of a creature he called a lemur into the exhibition catalogue of the Museum of King Adolf Frederick of Sweden in 1754 [PDF]. Four years later, he included it in the 10th edition of his Systema Naturae, assigning it to a new genus, naming it the Lemur tardigradus (literally the “slow-moving lemur”) alongside two more species he called Lemur catta (literally the “cat lemur”) and Lemur volans (the “flying lemur”). These three are the earliest lemurs on the zoological and etymological record—and Linnaeus clearly took his cue from the ghostly lemures of Roman legend when it came to picking their names.

It’s often been said that Linnaeus had the lemurs’ bizarre screeching, whooping calls in mind when he named them after the ghosts of Ancient Rome, or else their eerie reflective eyes, their silent nocturnal wanderings, or even the fact that they are considered the ghosts of ancestors in Madagascan folklore. But as Linnaeus himself straightforwardly explained:

"I call [the creatures in this genus] lemurs, because they go around mainly by night, in a certain way similar to humans, and roam with a slow pace."

Things have changed since Linnaeus classified the first of his lemurs in the mid-18th century. For instance, only one of his original three is still recognized as a true lemur today: Lemur catta is the Latin name of the ring-tailed lemur. His Lemur tardigradus is now identified as the red slender loris of the Sri Lankan rainforests, while the “flying” Lemur volans is now the Philippine colugo, a small tree-dwelling mammal similar to a flying squirrel. The fact that he classified the three as all belonging to one close family is also questionable, as lorises, lemurs, and colugos aren’t today considered quite as closely related as Linnaeus had presumed.

Nevertheless, the mythological name he chose for them has remained in use, and over time has gone on to become attached exclusively to the 100 or so species of primates native only to Madagascar. And there’s nothing scary about them at all.