10. WOLF
There are plenty of people afraid of the big bad wolf, and from all exterior appearances, who could blame them? A wolf's howl is enough to spark fear in even the most rational person. They're also twice as fast as an Olympic sprinter and can bring down predators that weigh five times as much as a human! Despite all these scary stats, the wolf threat factor is more or less one big fairy tale. There's never been a documented case of a wild wolf killing a person — in fact, they tend to be more scared of us than we are of them.
The mouse is yet another creature that in actuality is more scared of people than vice versa — but this little guy can still make us squeal with fear just by scurrying across the kitchen floor. Even though they're more or less harmless, the fact that female mice can have up to 11 babies every three weeks may be screech-worthy after all. Mice can also be scary for the economy, too; when they reach plague proportions, they can cause millions of dollars worth of damage.
If you're ever compelled to take a nice, refreshing dip in the rivers in the Amazon basin: unless you enjoy playing the part of a fish's chew toy, it might be best to skip it. The infamous piranha has quite the reputation when it comes to nibbling, though that term might be a bit misleading; a school of these fish can strip the flesh off of a cow in just minutes. Truth be told, piranha prefer to scavenge on animals that are already dead, and if that's not an option, they'll move on to the scales and tales of other fish. But with their tightly packed, interlocking teeth built for rapid puncture and shearing, it might be best to stick to swimming pools if you ever find yourself in South America.
Evander Holyfield may hold several belts and titles, but it's the grizzly bear who is the undisputed heavy-weight champion of the animal world, not to mention the biggest carnivore on four legs. As fast as it is deadly, the grizzly bear stands up to 10 feet tall, weighs more than seven men, and yet can outrun the best Olympic sprinter. They're also equipped with jaws of steel that can easily crush bone and a paw that can kill a human with one mighty swat. Though bear attacks are actually few and far between (hikers in the Rocky Mountains are more likely to be killed by falling tree!), this beast is easily the horror of the woods, hands down.
6. GREAT WHITE SHARK
What piranhas have done in terms of creating horrors in the Amazon River, great white sharks have done for the oceans of the world. Equipped with two tons of muscle and teeth, and averaging 20 feet in length, this is one big fish with an appetite to match. Despite their massive size, they move quickly, outpacing even the strongest swimmers with five times the speed. Though these facts and movies like Jawsmight lead you to believe otherwise, not all sharks are monsters; out of the 350 shark species, half don't grow longer than three feet, and despite press hype, there are less than 100 shark attacks each year worldwide. 
5. BAT
Bats get more silver screen time than any other animal in the horror movie genre. Classic tales like Bram Stokers' Dracula helped build the bat's scary reputation as blood-sucking killers. However, out of the nearly 1,000 different species, only three are actually vampire bats that drink blood. Some of the scarier things people associate with bats aren't actually true, so to set the record straight: they're most active at night and tend to spend the rest of their time in caves hanging out (upside down, of course) — sounds like the perfect opportunity for a rush of blood to the head!
Whether we're talking itsy bitsy or tarantula, spiders can spike intense fear in people, to the point that there's even an actual name for it: arachnophobia. Some arachnophobics get so bent out of shape by a spider's eight hairy legs and eyes and two horrific fangs that even a drawing of one can send them over the edge. Most spiders are actually unlikely to bite humans, and there are only five types equipped with venom strong enough to cause death.
Bee afraid ... bee very afraid. Sorry, couldn't resist, especially when faced with the alarming fact that over 2 million Americans alone are severely allergic to their venom. For this unlucky bunch, one single sting can be deadly in less than five minutes. The fear factor kicks up a notch if there's a swarm approaching. In fact, in the early 1990s, terror swept into the United States courtesy of Africanized honey bees from South America.
If a snake causes you to shudder, you're not alone; over half the population is scared of these slithering reptiles. While only 10 percent of all snakes are venomous, the ones that are deadly kill an estimated 30,000 people a year — and unfortunately, it's hard to know which side of the venom fence a snake lives on when first encountered. Of course, some are notoriously dangerous, such as the adult king cobra, which has enough venom to take out an elephant in a single bite.
Make no mistake about it: parasitic worms are truly the most horrifying creatures in the animal kingdom because they will literally eat you from inside out. One of the more exotic types, the blood fluke, lurks in the tropics and burrows through skin to enter the bloodstream, then heads for the bladder where they can reside for up to 30 years! Blood flukes will continue laying eggs that are so spiney they can rupture the bladder wall. For a gut-wrenching scare, look no further than the pencil-like round worm. One of out of every four people on the planet has one of these living in their stomach, feasting on the same food they eat. Or maybe you're being terrorized by a filarial worm, thin as a strand of hair or piece of thread, as long as your finger, and coiled up in your lymph glands feeding on your body fluids. Here's the scariest part: most of the time, you might never even know if or where a parasitic worm is lurking, making your body the ultimate haunted house.
