Mythical monsters that might have actually existed

History is riddled with stories of monsters that terrified our ancestors. Every culture has tales about beasts or creatures of some sort that attacked, or even killed, unsuspecting humans. Many of these stories were passed down as a form of warning, much like the urban legends and fake news you see your weird aunt post on Facebook.

But monsters aren't real, right? None of those things were ever proven to exist, and as time and science march on, mythical monsters have largely been disregarded in favor of actual human monsters, of which there seems to be no shortage.

So where did these monster myths come from? Certainly, some of them were purely metaphorical, meant to convey warnings about more banal dangers. But there are at least some mythical monsters researchers have discovered might have been based on actual things which just seemed a lot scarier before we began to understand them.

Hydras may have been based on real multi-headed snakes

In Greek mythology, the Lernaean Hydra was a multi-headed snake-beast confronted by Heracles, son of Zeus. Not only was the hydra fearsome, but Heracles also found it incredibly hard to defeat because each of the hydra's heads he lopped off quickly grew back. It wasn't until Iolaus, Heracles' nephew and occasional sidekick, got the idea to burn the stumps after the hydra was decapitated that Heracles was finally able to slay the monster.

While there weren't any 50-headed serpent beasts in Ancient Greece (hopefully), the concept of a hydra might have been based on something much less fantastical, but still quite remarkable. Ordinary snakes are common all over the world, and like many other animals, they can occasionally suffer from a condition known as polycephaly, wherein the snake can have two or even three heads, but can potentially otherwise be completely healthy.

While polycephalic snakes (or any other animals) are very rare, it would only take one or two sightings of one for it to turn into a telephone game of legends and myths. Modern biologists now consider snakes with polycephaly to be a very likely origin for the hydra myth, before artistic license turned them into monsters with dozens of heads, according to the BBC. Regeneration among reptiles is also not unheard of, which might have inspired the detail that their heads grew back, too.

Sirens were likely ordinary sea animals

History and mythology are full of aquatic humanoids, half-fish and half-human. Mermaids (or mermen, who just don't seem to be quite as interesting to us here on the surface world) are generally considered to be beautiful fish-women who largely avoid humankind but are otherwise not dangerous. Not so for their mer-cousins, the sirens, though.

Most famously seen in Homer's The Odyssey, sirens are more birdlike, often being depicted as having wings or even beaks, in addition to fish and human features. Sirens are said to sing a deadly but enchanting song that draws sailors into the depths. Odysseus' crew is able to resist by blocking their ears with wax and, in the case of Odysseus himself, being tied to the mast without the wax so he could hear the song (he was just into courting death, apparently), according to Ancient History Encyclopedia.

What might have inspired these legends is something we're pretty familiar with now, though. Modern researchers think ancient sailors probably saw manatees or dugongs, both of which have large arm-like flippers and can turn their head side-to-side, like humans, according to Smithsonian Ocean. From a distance, these creatures might look more human-like than they do close-up, and thanks to poor nutrition and mental strain from isolation, you also can't rule out those who saw sirens or mermaids might not have just hallucinated a few extra details.

Vampires were inspired by poor understanding of disease

Today, vampires have great PR and are depicted as slick, smart creatures, drinking blood from the living and hiding from humanity's watchful eye. But let us not forget classical stories of vampires. Typically, these involved lots of people dying all at once, someone blaming the deaths on a recently deceased person, that person is exhumed, and inside the coffin they find the deceased's hair and nails have grown, they have blood on their mouth or chin, and there are scratches inside of the coffin lid.

These kinds of stories are part and parcel of vampire legends, and several common pre-Dracula myths hit many or all of these points. But modern historians think what actually went on was much simpler. Disease was very poorly misunderstood, as was death. Remember that disease and how it spreads were largely unknown until recent times, according to National Geographic. Illnesses like cholera could quickly wipe out an entire town and leave them scrambling to figure out why.

On top of that, premature burial wasn't terribly uncommon and natural decay was a mystery. It's likely many "vampires" were actually people mistakenly buried alive or dead bodies undergoing ordinary decay that were misinterpreted as signs of vampirism, such as the body purging fluids through its mouth, which could be mistaken for blood, or "growing hair," which is actually due to the skin shrinking and exposing more of the root.

Giant apes were real, we just didn't know about them yet

From King Kong to Donkey Kong, giant apes are a big part of our culture. While modern stories about large primates focus mainly on Bigfoot, Sasquatch, the yeti, and so on, giant ape myths were actually fairly common in the past, too, albeit not as sensationalized. Instead of hairy, bipedal creatures with human-like features, giant ape myths were just that. Regular apes, only bigger.

These myths were especially common in places that actually have apes, such as the jungles of Africa. Throughout centuries of exploration, stories emerged of travelers encountering remarkably strong apes the size of a human or larger. African tribes had stories spanning back centuries about them. No evidence ever came forth regarding these giant apes, though, and so they were largely regarded as a myth or even a hoax, as noted by the Daily Telegraph.

It wasn't until 1847 that the truth was revealed: giant apes were actually real, and they were soon given an official name of gorillas. Before that, science had no idea gorillas were even a thing. Some of the legends about them were exaggerated, but there really was a species of large apes we just plain didn't know about. African peoples who had passed stories about giant apes through generations were thus permitted to tell western science "well, duh," or "told you so," as they saw fit.

Sea serpents were just really creepy sharks

Every seafaring culture has stories of massive sea serpents, thrashing through the water and occasionally threatening ships and sailors with huge, terrifying teeth. Norse mythology had one so large, called Jörmungandr, that it encircled the whole world. In Judaism and Christianity, a massive beast named Leviathan stalks the seas. Even more modern legends, such as those told by pirates, included these huge monsters.

While the natural conclusion might be to assume these legends originated from a misidentification of an eel of some kind, in truth, there's been something even scarier in the water for thousands of years. One of the oldest living shark species, the frilled shark (pictured) calls the deep sea its home, and like many deep sea animals, it looks super weird. Without the long fins we typically associate with sharks, the frilled shark wriggles through the sea and has multiple sets of barbed teeth, perfect for tearing things to shreds. Sightings outside of the deep sea are incredibly rare. The frilled shark is so old it's referred to as a "living fossil," according to National Geographic, because the species has barely changed in 80 million years.

Another possible culprit is the frilled shark's fellow deep sea denizen, the goblin shark. While not as serpent-looking as the frilled shark, the goblin shark is utterly terrifying, like something out of the Aliens universe. It'd be shocking if our ancestors didn't tell scary stories about them.

The Jersey Devil may not be a devil after all

In the Pine Barrens of New Jersey, legends tell of the Jersey Devil. According to the most common myth, the creature was the 13th child of a woman named Mrs. Leeds, who was so sick of having kids that she cursed the child and ended up giving birth to a beast with bat wings and hooves. While the story is nearly 300 years old, it really only became well-known in the 20th century, especially outside of New Jersey.

While sightings of the Jersey Devil do vary a bit, a few features are common. Long, slender legs, bat wings, and a long head. While it's not all that devilish, according to Cape May Magazine, there is a pretty common animal in the area that resembles the creature — the sandhill crane. It has slender legs, large wings, and a long head. It's not exactly terrifying, but it is a pretty decent fit.

Some rumors point to a much more interesting source, though: The hammerhead bat. Not only does it have the same features, but it does have bat wings and its head shape is almost identical to the most common depictions of the Jersey Devil. There's just one problem. The hammerhead bat is native to Africa, not North America, according to Snopes. It's not impossible hammerhead bats took up residence in the isolated Pine Barrens at some point, but this has yet to be proven.

Japanese river monsters were probably huge salamanders

In Japanese folklore, there are humanoid, amphibious (often depicted as turtle-like) creatures about the size of a child known as the kappa. They pop up a lot in Japanese mythology, but haven't really made their way across the ocean so much. Still, they do show up a little in the Harry Potter/Fantastic Beasts movie series, and plenty of anime and video games have nods and references to them.

Basically, they're mischievous gremlins that live in rivers and streams. They love cucumbers and, oddly, sumo wrestling. They usually pull mean-spirited but harmless pranks, but they can also sometimes attack or even drown unsuspecting humans. One interesting feature is they're usually shown to have a flat or bowl-shaped head which collects water, according to Mythology.net. If that water dries up or spills while they're on the surface, the kappa is severely weakened.

Many of these legends were based on sightings of a real animal, the Japanese giant salamander (pictured), according to Yabai. It's an amphibious creature, quite large, and it does have a flat head, which may have been where the detail about kappa having a flat or indented head came from. The salamanders are incredibly rare and endangered nowadays. They are protected by the Japanese government, so if you find one, maybe avoid sumo wrestling with it.

Voodoo zombies weren't created with magic, but with drugs

Before the flesh-eating zombies of The Walking Dead and George Romero movies were the concept of voodoo zombies — humans raised from the dead and forced to do the bidding of a voodoo practitioner. While these particular zombies didn't necessarily eat flesh, they were undead, shambling monsters. They may or may not decay like their modern zombie brethren, depending on the source.

Legends about these zombies went through centuries, and it wasn't uncommon to hear of a nefarious person raising the bodies of the recently deceased and using them like slaves. In fact, there were occasionally tales of former zombies returning to a more human-like state, as if they just stopped being dead after a while. 

In the 1980s, researcher Wade Davis headed to Haiti to look into this for himself. There, he discovered what may have been the concoction that made real-life zombies. The "deceased" weren't dead at all, according to Harper's Magazine. Instead, the unsuspecting victim was dosed with tetrodotoxin, found in the puffer fish, which caused a paralysis not unlike death that wore off in a few days. Davis came to believe victims were given this drug to make them appear to die, and then after several days, their "body" was retrieved and forced into servitude, where they would be given powerful psychoactive drugs on a regular basis to keep them pliable and obedient.

The wendigo is perhaps merely a state of mind

The Algonquian, native to the United States and Canada, have a legend of a beast called the wendigo. The legends vary. Sometimes the wendigo is a monster that eats human flesh, but in other cases, the wendigo isn't a physical being, but an evil spirit which possesses humans, causing them to become cannibals and perform other monstrous deeds.

You might recall the story, "The Wendigo," from Alvin Schwartz's Scary Stories to Tell in the Dark from when you were a kid. In it, an unnamed hunter and his native guide, DeFago, encounter a mysterious voice carried on the wind, which sweeps DeFago away. This is just one of many appearances of the wendigo in pop culture, and it is a bit toned down since there's no cannibalism, but it gives you an idea of just how spooky these tales can be.

Some psychiatrists think there's a less paranormal, but still creepy explanation. They call it "Wendigo psychosis," and according to American Myths, Legends, and Tall Tales, it's a cultural disorder specific to First Nations people. Effectively, the psychosis manifests as a belief one has been inhabited by the wendigo and causes the afflicted to suddenly crave human flesh. While the myth of the wendigo started out as just a story, those stories were so effective that wendigos became a self-fulfilling prophecy. Someone could become a wendigo by being afraid they were a wendigo. Try wrapping your head around that.

The little green men that weren't

On August 21, 1955, the town of Hopkinsville, KY was visited by unknown creatures. According to reports, 11 different people, mostly members of a family named Sutton, claimed to see creatures that looked almost like goblins. They stood about three feet tall with long arms that reached nearly to their feet and with large, pointy ears sticking out from their bulbous heads, according to History.

The Sutton family's friend, Billy Ray Taylor, claimed the creatures arrived in a small, metallic craft that dropped straight out of the air. The Suttons initially laughed at Taylor's story, but an hour later, their dog began barking. Upon going outside, the family and Taylor saw one of the creatures. The men present grabbed rifles and shot at the creatures, but they seemed to be impervious to bullets. After several hours, during which time the creatures peeked their heads into the house's windows and stood on the roof, the Suttons escaped and drove to the police station. While police assumed the Suttons had been dipping into some strong moonshine, it turned out they didn't drink, and no alcohol was found on the premises. Authorities found shell casings, but nothing else.

Researcher Joe Nickell proposed a much more down-to-earth explanation than aliens, though: The creatures were actually great horned owls. Comparing the drawings the police made with a photo of these owls, it's not hard to see a pretty striking resemblance.

Cyclops myths came from a very unexpected source

Greek myths feature several cyclopes, such as the one encountered in The Odyssey, Polyphemus. Like most others of his species, Polyphemus is a giant, one-eyed creature who happens to not be terribly smart. Odysseus is able to trick him (and later blind him) without too much effort by getting him drunk and telling Polyphemus his name is "Nobody." This sets up the greatest dad joke in antiquity when Polyphemus tries to tell his fellow cyclopes that "Nobody" attacked him.

Oddly, many cyclops legends are set on or around the isle of Crete. This might seem inexplicable without the historical context that Crete was once home to a species of dwarf mammoths (a total oxymoron) that were typically much smaller than an adult human, according to Nature.

What does that have to do with cyclopes? Well, historians suspect the myths originated from Greek explorers finding the skulls of these tiny behemoths. An elephant/mammoth skull has a large, central socket. It's for their trunks, not their eyes, but to someone who had never seen one before, it might look to be an oversized humanoid head with a central eye socket, according to National Geographic. So, working backwards from these skulls, the ancient Greeks imagined they belonged to 20 ft. tall monsters with a single eye and ran with it from there.

Giant sharks were more than just myths

The ancient Mayans have a creation myth where Cipactli, a giant sea monster often depicted with a single, huge tooth, was killed by Tezcatlipoca, and then he and Quetzalcoatl made the Earth from the monster's body. The Mayans weren't the only ones with stories of sea monsters with giant teeth, either. Many cultures have even created myths and legends about enormous, oversized sharks, far bigger than any seen today.

While there are some pretty large sharks out there, such as the whale shark, these mythological sharks are much bigger. Could there be some unknown, massive shark species out there that terrified our ancestors? Well, yes, potentially, there's tons of stuff in the ocean we don't know about. But what's more likely is these stories were inspired by the fossils of real sharks that went extinct long before humankind came along.

The megalodon, an ancient ancestor of modern sharks, was absolutely enormous, around 50 ft. long, according to the Natural History Museum. While megalodons went extinct over 2.5 million years ago, their fossils aren't exceptionally rare, and it seems the ancient Mayans found some of these, as they've been found in their caches, according to Live Science, and seemed to have inspired their legends about Cipactli. While the megalodons went extinct a very long time before humans came around, these giant fossilized teeth still freaked out the Mayans and several other cultures, as well.