Piranha: How Theodore Roosevelt Created a Flesh-Eating Myth

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Popular culture promises that a stumble into a South American river means a boiling frenzy of teeth and a polished skeleton in 30 seconds. The real piranha tells a different story. This episode traces the legend to a 1913 Amazon expedition by Theodore Roosevelt, when local fishermen netted off a stretch of river, trapped and starved thousands of fish, then pushed a cow into the water. Roosevelt described the result in his 1914 book Through the Brazilian Wilderness, calling them the most ferocious fish in the world.

The biology is stranger and more sympathetic. Piranhas are close cousins of the docile pacu and silver dollar, most grow only 12 to 35 centimeters long, and their jaws work less like scissors than like bolt cutters built for crushing force. They school out of fear, not to hunt, because dolphins, caimans, and cormorants treat them as a snack. Their diet includes fruit, seeds, and scales nipped from passing fish, which makes them closer to paranoid aquatic raccoons than river wolves.

• The name comes from an old Tupi word that first appears in a Portuguese-Tupi dictionary from 1585 and translates simply as scissors.
• A Miocene ancestor called Megapiranha lived about 8 to 10 million years ago and may have reached 128 centimeters, more than four feet long.
• In flooded forests, piranhas crack seeds that fall from the canopy, and one study found roughly 10 percent of stomach contents were seeds.
• Almost every documented attack on a human comes in the dry season, when fish are stranded in shrinking, oxygen starved pools and mistake splashing for dying prey.
• Around 190 bites were reported near Palmas, Brazil in 2007 and about 70 in Rosario, Argentina in 2013, nearly all single nips to the extremities.