Piranha's shouldn't be the feared things that they are. Only 4 out of the 18 species would ever really attack a human. Here is some basic info:
Teeth: The piranha's teeth are triangular and flat with needle-sharp points for piercing into the tough skin on prey. The sharp teeth can cut through bone, and are as long as ÃÂ½ inch!
Length: Average 8in. but some can be up to 20in. long.
Weight: no more then 3lb
Piranha's only live in and around South America. They are widespread throughout the rivers of Colombia, Venezuela, Guyana, Paraguay, Brazil, and central Argentina.
Piranhas live in packs, or shoals. They spend most of their time hunting for food. They mostly live in rivers but can also live in lakes, or anywhere there is enough food but within their natural habitat.
The piranha hunts with speed and by surprise.
The typical way they attach is by swimming directly into a shoal of fish. Small fish are swallowed whole, while large prey have chunks ripped out of them.
Piranhas have a "advanced" sense of smell, which help them to locate prey. The presence of blood in the water will send them into frenzy. They are also very good at detecting vibrations in water.
Piranhas will eat anything. They will attack any animal that enters the water though human contact is rare. Some piranhas are vegetarians which most people don't know.
Because they will eat any prey and are not liked by fisherman, non-of the 18 species are in any danger.
Humans try to avoid contact with this species.
They will eat anything, and are very aggressive.
There are lots of scientists out there studying the piranha. They are currently trying to figure out exactly what the danger to humans is,