Bats are actually a pretty helpful member of the ecosystem that, depending on the species, can help to pollinate plants and gobble up troublesome insects, according to the National Science Foundation. But they also have a spooky reputation and very often turn up in Halloween decorations.
True to their nature, some bats may have been attracted to the tasty insects drawn by Samhain bonfires, says Popular Science. Many bat species are also nocturnal, further increasing their supposed association with ghosts, pagan deities, and the underworld. It's unsurprising that in the popular imagination, they have gone from a pretty innocuous if cool-looking flying mammal to a harbinger of Halloween tidings.
Meanwhile, the witchy reputation of black cats made them an easy fit for the spooky holiday. After all, how often do you see a ginger or tabby cat in a Halloween display? According to American Folklore, the association between Halloween and black cats may have started in the Middle Ages, when people were often frantically working to root out evil witches in their midst. Those cats, with their eerie dark coats, were frequently associated with evildoers working at night. Some even believed that black cats were witches who had the power of transformation at their disposal. Soon enough, the black cat gained an eerie reputation, which was further spread when European immigrants took their tales and traditions across the Atlantic Ocean to the Americas.
