Fearsome Piranhas: Calculating Their Human-Eating Speed

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The world of cinema and video games have made us believe that piranhas are much more dangerous animals than they really are. Just as with the wolf or the shark, seeing them attack our favorite characters, as in the case of Lara Croft and the Tomb Raider saga, leads us to think that we are facing carnivorous fish capable of eating a human in a matter of seconds. But is it really like that? How long would it take piranhas to eat a human?

First of all, it’s time to demystify piranhas. Although there are species of carnivorous piranhas, most of them are omnivorous animals or even herbivores, their favorite delicacies being pieces of fruit, plants, insects or mollusks. In the case of meat lovers, if they have to attack they will do so on other fish, usually smaller than them.

Do we then rule out that they can eat a large mammal? Not completely, but we must bear in mind that despite their sharp teeth, they will only do so if they find a dead or very badly injured prey, and to venture into this we would have to be in front of groups of carnivorous piranhas (they usually move in flocks of between 10 and 100 piranhas) that, due to the lack of their most common foods, are very hungry.

To continue with the assumptions, let’s imagine that a man falls into the Amazon, where this species is natural. According to what one of the people in charge of the New England Aquarium told Live Science magazine, she applied the idea of a dog to the case.

A piranha weighs about 541 grams and usually eats about 12 grams of food in about 30 seconds. However, if we are dealing with very hungry piranhas, there have been cases in which they have come to ingest up to 68 grams, which is one eighth of its body weight.

Now let’s imagine that a seriously injured human weighing about 80 kg has just fallen into the water. If we subtract bones and so on, we are left with 60% lean body mass, around 48 kg of meat, so to devour his entire body we would need a total of 706 adult piranhas terribly hungry so that the corpse remains in the bones. And to get to that point, they would need about 9 minutes to complete the process.

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