Why Piranhas Are Continually Misunderstood As Aggressors

In a captivating TED-Ed lesson written by zoology expert Antonio Machado-Allison and animated by Anton Bogaty, narrator Addison Anderson explains the behavior of the sadly misunderstood piranha. As it turns out, piranhas, particularly the red-belly variety, are not aggressive and actually shy away from human contact whenever possible. In fact, they will only attack under very specific circumstances.

Well, when they do bite people, it seems to mostly happen in scenarios when they’re being handled; when people are spilling food or cleaning their fishing catch in the water; or when people disturb piranhas while the fish are mating or guarding their eggs during the wet season. Starvation stress is also thought to lead red-bellied piranhas to increasingly bold, aggressive behavior.

The fear of these toothy fish began with President Roosevelt’s misleading impression of them.

In 1914, he published a bestselling book in which he called piranhas “the most ferocious fish in the world” and wrote that the scent of blood could incite them to rapidly devour an entire cow— or human— alive. But Roosevelt’s account is generally considered circumstantial and misleading. The “feeding frenzy” he witnessed is suspected to have been the result of people purposefully starving red-bellied piranhas, then giving them the opportunity to feed on a cow carcass— all to put on an exciting show.