Why Piranhas Aren’t Nearly As Scary As You Think

“It’s like the Nature Channel. You don’t see piranhas eating each other, do you?” —Mike McDermott, “Rounders” (1998)

In A Nutshell

Even today, piranhas are known as one of the most brutal of all fish. That reputation is largely undeserved, though. Most piranhas are scavengers rather than hunters, preferring to feed on the dead or on the cast-off leftovers from a fisherman’s gutted catch. Some are even vegetarian. The whole idea of the savage piranha started with Teddy Roosevelt, when he wrote on them for his 1914 book, Through the Brazilian Wilderness.

The Whole Bushel

When it comes to terrifying marine life, piranhas are right up there with sharks, right? We’ve all heard the stories of razor-sharp teeth and their ability to devour an entire cow or a whole person in mere minutes.

Well, that’s a major exaggeration.

In fact, recent research done on piranhas with the deadliest reputations, the red-bellied piranhas, suggests that they’re far from dangerous and that they actually make fairly harmless swimming companions.

Even today, headlines from barely-better-than-toilet-paper “news” organizations like the Daily Mail still insist on running stories about deadly piranha attacks. Movies feature the idea relentlessly, with every film set in the Amazon seemingly required to include one terrifying scene of the erstwhile hero facing a river churning with snapping piranhas hungry for flesh and blood. But when wildlife writer Richard Conniff got up close and personal with some of the supposedly deadly fish, he found they were quite pleasant.

He went swimming with them in a Dallas Aquarium, stood in the Rio Napo and fished for them while they swam around him, and fed chickens to groups of them to see how long it would take them to devour the whole thing.

It took quite a while—even at the end of the day, it was mostly intact.

When Conniff spoke with fishermen who lived and worked alongside the notorious fish, he found that those who lived nearby agreed that the reputation of the piranhas had been blown way out of proportion. Those who live there (and others who have spent time studying the behavior of piranhas in the wild) have found that piranhas are more scavengers than hunters.

There are few actual cases of piranhas swarming and attacking living people. Most of the damage done to bodies that fall in the water is done post-mortem. And in most of the cases where piranhas have been known to bite people, there’s usually another factor that’s overlooked in the reporting of the story. Piranhas will stake out an area where fishermen go to gut their catches and throw the remnants overboard, and they’ll also lurk under the nesting grounds of birds, waiting for babies to fall in the water. When humans get bit, they’re usually just collateral damage.

Article Continued Below

The bite force of a piranha has also been greatly exaggerated. While some species can exert quite a bit of pressure through their bite—the redeye is capable of dishing out a force three times its own body weight—that’s nothing compared to ancient piranhas. The toothy fish are millions of years old. Over the centuries, they’ve gotten smaller and lost an entire row of teeth.

While some piranhas are cannibals, some are vegetarians as well. And piranha experts have estimated that in order to demolish the entire body of a cow in the frequently quoted five-minute time frame, that would require the presence of somewhere around 500 hungry little fish.

So where did all the piranha hate come from? Teddy Roosevelt.

In Roosevelt’s 1914 book Through the Brazilian Wilderness, he tells some tall tales about the piranha. According to his work, they don’t swim, they swarm. They mutilate swimmers, he says, and he claims to have met countless locals who bear scars from the fish. Even out of the water, they remain dangerous and can survive for some time.

He writes, “They are the most ferocious fish in the world. [ . . . ] They will rend and devour alive any wounded man or beast, for blood in the water excites them to madness.”

Later, he tells a story of a 12-year-old boy who was attacked while swimming, eaten alive by the fish. Then there’s the story of a party of explorers who threw dynamite into the river to make short work of fishing. When fish floated to the surface, the hungry men gathered them up for a meal. The unluckiest of them didn’t notice he was munching on a piranha until he’d bitten into the fish. It took off most of his tongue.

We’ll likely never know if he really heard these stories and believed them or if he embellished them himself. Either way, they make for good campfire tales.

Show Me The Proof

Through the Brazilian Wilderness, by Theodore Roosevelt
Smithsonian: 14 Fun Facts About Piranhas
NY Times: Shocking Truth About Piranhas Revealed!