Is it possible for piranhas to reduce a cow to its skeleton in less than 60 seconds?

During his 1913 hunting trip in Brazil, Theodore Roosevelt witnessed a dramatic spectacle. From the banks of the Amazon River, he observed piranhas attacking a cow with astonishing brutality. The scene was unforgettable: the water churned violently as piranhas swarmed, blood spreading everywhere, and within moments, a skeleton emerged from the now-still water.

Roosevelt was deeply disturbed by the experience and extensively documented his encounters with these fierce creatures in his 1914 book, "Through the Brazilian Wilderness." He shared tales of locals who had been consumed alive and others who suffered severe injuries while swimming in the river. "They are the most savage fish on the planet," Roosevelt declared. "They can sever a finger carelessly dipped in the water and maim swimmers—every river town in Paraguay has victims of such attacks. They will tear apart and consume any injured animal or person, driven to frenzy by the scent of blood" [source: ESPN]. Thus, the piranha legend was born.

Hollywood embraced the piranha legend with the 1978 horror film "Piranha" ("Flesh-eating piranhas accidentally released into a resort's rivers turn guests into their prey"), followed by 1981's "Piranha II: The Spawning," and a 2010 remake of the original cult classic [sources: IMDb, Movie Insider]. The deadly piranha has successfully transitioned into the 21st century with its gruesome reputation intact.

But does the piranha truly deserve its fearsome reputation? Roosevelt's infamous cow-stripping incident occurred in Brazil, where piranhas thrive in large numbers. However, these fish are widespread throughout South America's Amazon River, ranging from Argentina to Colombia. Are South American cattle a common food source for these aggressive fish? And why are cows even found near the Amazon River?

Putting aside the dramatic account of a former U.S. president, the idea of piranhas reducing a cow—or a human—to a skeleton in under a minute seems far-fetched. How could a group of 10-inch, 3-pound fish accomplish such a feat?

Let’s explore the truth behind this myth.

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Piranha!

Roosevelt ventured into the Brazilian Amazon as an enthusiastic hunter, far from an ordinary traveler. As a former U.S. president, his guides aimed to ensure his satisfaction. What he observed, however, was genuine: piranhas devouring a cow to its skeleton in an alarmingly brief time. Whether it took less than a minute remains uncertain, but such an attack is within the realm of possibility for piranhas. Roosevelt’s experience involved unique conditions, which we’ll explore later. Regardless, the sight was unsettling, especially given the small size of these fish.

These are not monstrous creatures. Piranhas typically grow up to 2 feet (60 cm), but most measure around 8 inches (20 cm) in length and weigh only a few pounds. Among the approximately 20 species in the Amazon River, the red-bellied piranha (Pigocentrus naterreri) is one of the smallest and most aggressive, weighing about 3 pounds (1.36 kg) [source: ESPN]. The black piranha (Serrasalmus rhombeus), another aggressive species, is generally larger than the red-bellied variety.

For piranhas, size isn’t the key factor—it’s their teeth that make them formidable.

A piranha’s teeth, though only about a quarter-inch (4 mm) long, are razor-sharp, and their jaw structure is optimized for efficient biting. The teeth are arranged in an interlocking pattern, so when the jaws close, the upper and lower teeth mesh like multiple pairs of sharp scissors. Their jaws are exceptionally powerful: some individuals who have lost toes to piranhas have had the entire toe, including the bone, cleanly severed.

Piranhas can rapidly reduce a large animal like a cow to a skeleton due to several key factors. First, piranhas don’t chew their food. When they bite, large chunks of flesh are swallowed whole, allowing them to consume quickly. Additionally, such feats are achieved by hundreds of piranhas working together, far exceeding the typical school size of 20. During a feeding frenzy, they rotate efficiently, each taking a bite before moving aside for the next piranha. This rapid rotation creates the boiling-water effect, as the fish constantly shift positions.

Another critical factor in piranhas devouring large animals so quickly relates to the specific conditions Roosevelt witnessed. Feeding frenzies occur when piranhas are starving, which is not a daily event. Roosevelt’s guides had orchestrated the scene by isolating a section of the river with nets and trapping hundreds of piranhas. By the time the cow was thrown in, the piranhas had been deprived of food for an extended period.

If consuming an entire cow in under a minute isn’t typical, what do piranhas usually eat, and how do they feed?

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Piranha Feeding: The Daily Grind

While piranhas can attack live animals, it’s unlikely they could overpower a healthy, fully grown human. However, they have been observed targeting weak or elderly animals that approach the river to drink. When a cow lowers its head, piranhas may latch onto its face. If the cow is too feeble to resist, the piranhas can drag it into the water and consume it. Still, live prey isn’t their primary food source. Piranhas are mostly scavengers. The skeletons of animals and humans found in the Amazon, seemingly devoured by piranhas, were not attacked alive—they were already dead when the piranhas fed.

Like many other fish, mammals are not a significant part of the piranha’s diet. They primarily feed on other fish, including their own kind. For example, a Welsh aquarium that went to great lengths to obtain a male and female piranha (piranhas are illegal to import in many regions, including Britain) hoped they would breed. Instead, the female ate the male [source: BBC News]. Piranhas aren’t strictly carnivorous, though. They also consume fruits and plants, especially during their younger years.

Contrary to popular belief, most piranhas are not aggressive attackers. Twelve of the 20 Amazon species survive solely by nibbling on the fins and scales of other fish as they swim past. The affected fish swim away with minor disturbances, and their fins and scales eventually regenerate.

Although piranhas are not the ferocious man-eaters of legend, human attacks have become more frequent. In South America, incidents of people losing fingers and toes have risen compared to a decade ago. Experts suggest this may be linked to the increasing number of dams on the Amazon River. Dams slow the water flow, creating ideal breeding grounds for piranhas, which prefer calm waters. These placid areas also attract swimmers, leading to more frequent encounters between humans and piranhas.

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Can piranhas really strip a cow to the bone in under a minute? Author's Note

Articles like this one, which delve into popular myths or widely accepted "facts" to uncover the truth, fiction, or lingering mysteries behind them, are among my favorite to write. This particular piece made my heart race when my editor assigned it, as I recalled believing I had encountered piranhas during a scuba-diving trip years ago.

I soon discovered I hadn’t, as my research and examination of piranha images revealed. In fact, I wasn’t even in South America at the time.

As for real piranhas, the cow myth proved to be surprisingly accurate, even if the incident Teddy Roosevelt described was staged (that unfortunate animal). Those small fish had indeed stripped a cow of its flesh in record time. While this isn’t their usual feeding behavior, it’s oddly fascinating to know it’s possible—and it’s enough to deter me from swimming in the Amazon if I ever visit. Whether it took one minute or three seems irrelevant.

Sources

Piranhas: Cheat Sheet

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