When a "fact" gets repeated often enough, it becomes lore, and sometimes even an idiom. You've heard "blind as a bat" and "the wise owl" so many times it seems natural, but neither is true. Bats aren't blind. Sure, they use echolocation, but that's because they fly in the dark. It's hard to see in the dark no matter how good your eyesight is. Owls may look wise, and they are in many storybooks, but studies show they have more trouble learning a new task than other birds do.
Sometimes even the refutation of an old wive's tale can be inaccurate. The custom of bullfighters waving a red cape was once explained as their way of enraging the bull for a fight. That was later "debunked" by the "fact" that cattle are colorblind. The real story is that bulls can indeed see red, but they have trouble distinguishing blue from green. Whether red actually enrages them is another story. Okay, how many other often-repeated commonsense "facts" about animals can you think of? They may likely be pure myth. Mental Floss has a list of 64 misconceptions about 63* different animals they will happily debunk for you.
* The list says 64 different animals, but both cows and bulls are in there, and they are the same species.