Piranhas are generally not harmful to humans; though known for their sharp teeth and occasional aggression, attacks on people are rare and usually occur only if the fish are provoked, food is scarce, or they are defending their eggs. Serious injuries from piranha bites are uncommon.
Piranhas are native to South America and are commonly found in countries such as Argentina, Brazil, Bolivia, Colombia, Ecuador, Guyana, Paraguay, Peru, Uruguay, and Venezuela, inhabiting rivers like the Amazon, Paraguay, and Paraná.
Piranhas can show aggression, especially when in large groups, during times of hunger, or when protecting themselves or their spawning sites, but they generally do not attack humans unless they feel threatened.
Piranhas have several natural predators including larger fish, birds like herons and kingfishers, caimans, anacondas, and aquatic mammals such as otters, which help control their populations in their natural habitats.