Few animals of the world have been more vilified than the piranha. Sure, they look like an aquatic minion of Satan and can devour a chicken in mere moments, but the monstrous creature depicted in cheesy Jaws-inspired horror movies is often blown out of the water. If the piranhas’ PR team were to sniff out where this nasty rumor originated they would undoubtedly be led to one man: Teddy Roosevelt.
Following a crushing defeat to Woodrow Wilson in the 1912 US presidential election, Theodore Roosevelt set out on an expedition down the unexplored "River of Doubt," since renamed the Roosevelt River, in the depths of the Amazon basin.
Nineteen men set out on the expedition, but just 16 returned alive. Pretty much everything that could go wrong went wrong: disease, injury, food shortages, exhaustion, drownings, murder, you name it. Roosevelt himself returned to the US on death's door due to a wounded leg that had become deeply infected.
Regardless of the trip's many setbacks, Brazil was honored by the visit. Roosevelt was the first North American statesman to visit the Amazon jungle and they were keen to impress him and his troops with some "authentic" Amazonian entertainment.
According to an account by tropical fish expert and writer HR Axelrod, local fishermen isolated 90 meters (300 feet) of the Rio Aripuana with nets and spent weeks feeding the cornered-off area with hundreds of piranhas. Roosevelt’s crew were told no one enters the river due to its ferocious inhabitants. To prove this, the locals brought over a sick, aging cow and pushed it into the river. The starved piranhas made quick work of the unlucky cow. A flurry of splashes rippled on the water’s surface and a cloud of murky red spread out. Minutes later, the picked clean skeleton was drawn from the water for the onlookers to appreciate.
The event, evidently, left quite the impression on Teddy.
In his book about the expedition, Through the Brazilian Wilderness, Roosevelt wrote: “They are the most ferocious fish in the world. Even the most formidable fish, the sharks or the barracudas, usually attack things smaller than themselves. But the piranhas habitually attack things much larger than themselves.”
“The razor-edged teeth are wedge-shaped like a shark's, and the jaw muscles possess great power. The rabid, furious snaps drive the teeth through flesh and bone. The head with its short muzzle, staring malignant eyes, and gaping, cruelly armed jaws, is the embodiment of evil ferocity; and the actions of the fish exactly match its looks.”
None of this is to say that piranhas are pushovers – given half the chance, they will happily chomp off a finger or take a bite out of a human. Nevertheless, a scientific study from 2003 found there were very few documented cases of humans being eaten by piranhas, and at least three of them occurred after the person had died of other causes, such as drowning or heart failure.
The study also notes most cases of piranha attacks consist of just a single bite. In the huge majority of cases, you could have a quick swim in a piranha-filled river without too much trouble. Some species, especially red-bellied piranhas, can be aggressive if they're starving or provoked, but most would much rather dine on a fish or a rotting carcass, rather than a swimming human.
Just remember to count your toes after you dry off.