[WARNING – some graphic material] The Piranha is a fish of many complexities and traits. However, it is known for one thing, the much fabled frenzy that strips mammals to the bone. So if this happens, why indeed, does it happen? What prompts the Piranha to attack in numbers so ferociously.
In short, despite the best efforts of Hollywood and adventure novels, an attack or frenzy is not a certain occurrence in the wild. Humans and Piranha can exist in the same water space. Piranha attack individually when they are attacking other fish and attack in numbers when the meal is considerably larger than they are. They will also ‘frenzy’, only when they are convinced the meal is dead, and thus are safe from attack themselves. The Piranha has many large predators itself, such as dolphins and caimans and will tend to avoid larger animals. Humans have been bitten, with attacks mainly on feet and fingers when they feel threatened, or nests have been disturbed. They tend to bite ‘once’ as a warning and most humans who get bitten walk quite safely out the water. The much fabled ‘frenzies’ are on large, already dead or immobile animals. They can be artificially induced by placing dead meat within a school of hungry Piranha.
The Piranha is Attracted to Noise, Splashing and Blood
Piranha, while in their natural habitat, will be quick to react to noise, splashing and blood. The sound of noise reminds them that it would be possibly feeding time as fruits will be falling from trees. Splashing by other animals could be a sign of threat and the Piranha will stay alert when they hear splashing water.
Splashing could also indicate that it might be a dying animal struggling to survive and this could be a potential meal for the Piranha fish. The fish will possibly move towards the direction of the splashing water to as they hunt for food.
The smell of blood in water indicates that this could well be an injured animal. An injured animal is in no position to fight back, and hurt the Piranha. Thus blood in the water is a potential target for a meal. Piranha do not attack animals preferentially, as they are opportunistic feeders who depend on dead animals or severely injured animals for meat.
All of this was confirmed in a study done in 2007.
It uses these senses to hunt and scavenge for food, not to find prey.
The Piranha Senses Used for an Attack
Sensitivity to Noises
When attacking, just like any other animal Piranha will have some senses which are best suited to attack their prey. They have highly developed sense of hearing which makes them sensitive to the slightest noises in the water.
They can hear noises of very low frequencies even at very long distance. The sense of noise according to fish experts, helps the Piranha fish that there could be potential fruits or seeds that are falling into the water en masse. This is obviously useful as it could be a potential meal for the fish.
Therefore is you are swimming in water infested by the Piranha fish you should always avoid making noise as it would attract the fish. They could bite you as they might mistake you for food, although this is unlikely.
Sensitivity to Splashing of Water
The Piranha’s lateral line is highly sensitive to hydro-logical changes in the water and this includes temperatures changes within tides and waves.
The lateral line is a complex system of sense organs primarily used to detect vibrations, movement and pressure changes.
The sensitive lateral line enables the fish to capture the waves created by splashing water. Dying animals usually create splashing as they struggle for survival, the weak animals is potential prey to the Piranha fish.
A struggling prey fish also gives off the same underwater sound waves. There is an uneven symmetry of motion that is picked up by the Piranha’s lateral line.
Sensitivity to the Smell of Blood in Water
Piranha fish can smell a drop of blood in about 200 litres of water. The Piranha fish is omnivorous, and apart from eating plants they will feed on weak and dead animals. The smell of blood indicates that an animal could be potentially injured and would be a target for the fish.
They will quickly move towards the smell of blood and will attack a dead animal. If they are moving in a shoal of fish, a feeding frenzy could be witnessed especially if the fish have gone for days without food.
If you have a wound it might not be a good idea to swim in water infested by the Piranha as they might bite you as they would mistake you for a dying animal, and they could injure you badly.
The Typical Diet
A Piranha’s typical diet depends with their age, gender and the specific species of the fish. The young Piranha, known as fry, when they are hatched start by feeding on sea algae and parts of the plants.
Piranha will rarely attack an animal bigger than its size unless an animal is dead or is weak, therefore Piranha will rarely attack humans. Piranha attacks are mostly exaggerated by the media.
Some Piranhas are exclusively herbivores while most of them are omnivorous in nature. Fish experts say that they are timid and shy, but the Black Piranha and the Red-Bellied Piranha are the most aggressive.
The Black Piranha in particular has one of the most powerful bite compared to its body mass.
Built for an Attack
The body structure of the Piranha fish is built for attack. The jaw for instance is very powerful with teeth which are chisel shaped arranged in a single row within the jaw. The enamel of the Piranha tooth is very strong and fish experts sometimes compare it to that of the shark.
The middle tooth is slightly raised above the rest of the teeth, making it easier for the fish to attack its prey and tear it into pieces.
Moreover, the fish can replace their teeth even when they grow old making it easier to attack other fish throughout their lives. The body of the Piranha fish is streamlined such that the head is small and blunt for penetrating through the waves of the ocean.
The Piranha fish will move at a very fast speed when they are attacking their prey giving the prey little chance of saving itself from their jaws.
It’s a fast fish, and in bursts of speed can reach 15 to 25 mph, depending upon size.
So it is fast, powerful fish with a streamline build and razor sharp teeth. Millions of years have honed this scavenger to perfection.
Razor sharp teeth seem a little overkill for a scavenger, and this is presumably where the myths come from.
When Do Piranha Attack?
It’s known that the Piranha fish will not bite people who swim in the river, nor any other animal that is bigger in size. Like any other wild animal, Piranha fish will react by biting during certain situations only.
First they will bite when they feel like they are being threatened, either personally or a wading human who is about to step on their nest in the vegetation. Unlike most fish, Piranha have a strong parental instinct, and they will protect their young ones till they are capable of defending themselves.
If you approach a nest of young Piranha or Piranha eggs you might be bitten by the parent fish. To avoid trouble you should avoid their breeding sites as this invokes aggressive behaviour. Avoid vegetation in low water levels for this reason. Therefore if you are about to disturb a nest, protected by both the male and female, you will mostly be bitten by the male as a warning.
During the low waters, and the droughts the fish are exposed to irritants in the environment, and normally the fish live in the deep waters. During such times there is scarcity of food, within their natural environment they will bite you as they are prone to biting as they are looking for food.
The fish will however not eat you as they will just take of some flesh from your body by biting and run off as they fear that you might fight back. Avoid swimming in Piranha infested water when the water is very low as you might be risking being bitten by the fish.
The fish is sensitive to triggers, and as such is sensitive to the smell of blood in the water.The smell of blood would be an indication of an injured animal which the fish could prey on. If you have a wound the fish might attack you as they could think that you are dead or weak, and would think that you are potential prey.
If you are swimming in a river infested in Piranha fish you should avoid splashing the water as this also triggers the fish, the sound of splashing water is related to dying fish that is potential prey to the Piranha fish.
Noises, triggers the sound of falling fruits and is not advisable to make noises in rivers infested by Piranha fish as they might attack.
From the Piranha point of view it has to be very careful before an attack. There are plenty of animals that prey on the Piranha as a food source and the Piranha is reluctant to tangle with larger animals by choice.
How Piranha Attack Fish
Being an omnivore, the Piranha will eat seeds, fruits and plants occasionally. However, it is prone to meat. While crustaceans are on their diet, they are often known to attack other fish.
If that fish is injured, then it has a greater chance of being attacked.
In 1972, a study on Animal Behaviour decided to find the answer to the Piranhas attack preferences.
A number of Red-Bellied Piranha were exposed to a goldfish for a single day for 30 days. They found that in nearly 90% of cases the first strike was at the tail. The remainder of the time the strike was at the eyes of the goldfish.
It was concluded that Piranha fish will immobilize their prey before attacking fish similar to them in size. They will nip the eyes and the tail fins especially in an enclosed place like the aquarium where they will feel threatened.
By doing this they can overpower the fish, and it was decided that this was a successful survival strategy, as it reduces risk to the attacking Piranha and effectively immobilises the prey.
The Black Piranha is a solo fish and would do it alone, but the Red-Bellied Piranha would do this more likely in a shoal.
This video shows an injured fish being attacked by Piranha
Attacking Large Animals
Piranha fish will not normally attack animals bigger than their size, even their shoal size, they will think that you are a predator.
Ironically the Piranha is more scared of you in the water than the other way around. Big animals in the water are normally predators, not prey.
Like any other animal they will avoid animals which threaten their peace. In situations when the large animal is dead they will however attack and strip off their flesh. If an animal is severe sick or weak the fish can however attack the animal.
What has typically been noticed to happen is this;
- A large mammal is in the water, floating downstream
- A group of Piranha will have been attracted by blood or other senses.
- The Piranha will not immediately attack
- A lone Piranha will quickly take a bite if it seems non threatening
- If the prey does not show signs of life, the rest of the shoal attacks
You can see by this method that a Piranha school can ascertain if they are scavenging or risking their own lives. If on the first bite, there is sign of life, then the school can quickly disperse with as little risk as possible.
There is safety in numbers it seems.
Watch this to see this sequence in action
If you fall into the water by becoming unconscious, you might be attacked by the Piranha fish but they will not attack you if you do not feel like you are weak. A moving large animal is a threat.
Most humans found with Piranha bites are thought to have drowned first.
To back this up, there have been several noted attacks on humans, where they have received one attacking bite, and by displaying evidence that they are alive, this has not resulted in further attack and they have walked out of the water.
Why do Piranha Attack Each Other
Piranha fish will nip of fins of other animals that pass-by, in an aquarium they will nip off fins of fellow Piranha fish. Black Piranha especially.
If a Piranha fish dies other fish will feed on it. During times when there is food scarcity, the fish will show signs of cannibalism as they struggle for survival in their natural environment.
The Piranha will however show signs of cannibalism when there is scarcity of food, especially during the dry seasons in the Amazon region.
The Feeding Frenzy
There is such a thing as a Piranha feeding frenzy though. So what is it and what has occured?
The legend of the feeding frenzy is somewhat attributed to President Roosevelt and his adventure in the Americas. He witnessed a shoal of Piranha fish feast on a cow, devouring it whole in a few minutes. Fish experts, however say that it would have taken a minimum of 500 fish to have achieved that timeline and would have to have been starved to eat a cow within that time frame.
During a feeding frenzy when there is lack of food in their natural habitat, a shoal of Piranha fish which contains at least 20 fish or more, will feed on weak or dead animals. One fish will bite the dead animal in a first strike to test the prey. In instances when the prey does not respond, the rest of the fish will pile on, taking turns with attacking the weak animal.
A very large animal can see many fish attack at the same time and the water can look alive.
This is one of the methods of survival for the species. During frenzies, the fish bite the animal in a large group and the water might turn red as the flesh of the animal is stripped.
When seen, it is quite a sight to behold;
Do Piranha Attack Humans?
Firstly, Piranha attacks are wildly exaggerated. Despite the scary precedence in folklore Piranha are wary of humans in the water and most attacks are attributed to drowned people being scavenged, not attacked while alive.
The idea that Piranha fish can strip off flesh from human bodies is more of a myth than a fact. It might require more than 200 Piranha fish to strip off flesh from a person.
With humans, it is most likely they were attacked after death by some other cause. Those seem to be the preconditions for the Piranha to attack you.
Reports on deadly attacks by Piranha are highly exaggerated by the media. For instance, the dead Brazilian girl in 2012 who was washed off a capsized boat might have died before sustaining Piranha bites.
Most of the people who live in the Amazon region say that attacks by Piranha is merely come from the vulnerability of the victim.
During the summer holidays however there have been incidences of Piranha attacks on swimmers when the water levels are low and there is scarcity of food.
The Piranha bites are however limited to bites on the toes and the hands which do not cause adverse injuries on an individual. It is thought more of a cornered warning than an attack.
Jan Mol, a fish expert in Suriname conducted an experiment by splashing and making noises during feeding time, but the Piranha did not attack him.
In Suriname there was an incident of a girl who had been bitten by Piranha fish, Jan disputed that the fish had killed the girl as he said that the media had exaggerated the news.
Hypothetically How Would Piranha Attack Humans
So mostly Piranha are wary of humans in the water, as a precaution against real predators, but hypothetically several conditions would have to be met
- The Piranha would have to be very hungry to risk it
- You would have to be threatening the Piranha for it to see a bite as self defence
- For an attack to happen you would have to be incapacitated or unconscious
Piranha attacks happen when the prey is easily attacked or vulnerable. The piranha fish can smell blood in water as they have a strong sense of smell. If you are bleeding the fish might think that you are weak and vulnerable and could bite you.
If you make noises and splash water the fish might confuse the sound of noise for falling fruits and the splashing of water for injured fish and could target and bite you as they are searching for food.
You should avoid making such noises in Piranha infested water to stay out of trouble.
People who drown in Amazon water, or those who might be very weak to the point of failing to defend themselves might fall prey to the Piranha fish. They however do not attack people as they think that they are predators and will avoid swimming towards people since it is a shy fish.
Aggression is triggered when they are threatened or hungry evidence of a lack of food sources might be more likely to precipitate an attack.
Most likely to be Red Bellied or Black Piranha as well, as these are known to be the most aggressive of the Piranha species.
How Many People Are Known to Have Died from Piranha Attacks
The Amazon basin is home to about 20 million people spread all over 8 countries. It consists of fishermen from small to large communities living around off the plentiful natural produce.
It is reported that there are at least 200 Piranha attacks yearly making the attack by the fish a minor incident which should not raise concern for the safety of the people living in the Amazon basin.
When the Piranha fish attack humans, usually for being threatened unintentionally, it results in minor injuries on the toes and the hands. Over the last 10 years, most attacks in the Amazon region have been reported to be minor bites. These bites do not cause fatal threats to a person, as they are easily treated by visiting a doctor or the simple dressing of the wound.
In 2011 a drunk man in Rosario Del Yata fell in the water. It is speculated that he was attacked and killed by the Piranha fish.
In 2012, a Brazilian girl, who fell in water, drowned and was attacked and killed by a school of Piranha fish. In this case the Piranha attack was not the cause of her death.
Stories of another girl who drowned and was killed by Piranha fish circulate, but Post Mortem results for this victim, however indicate as well that she might have drowned, before she sustained the Piranha bites.
In short, the exact number is not known on an annual basis but is thought to be negligible.
Piranha will quite happily attack while humans are in the water
Stripping Mammals to the Bone
After an adventurous visit to the Amazon region, President Teddy Roosevelt articulated that he saw a pack of Piranha fish feast on a cow in a few minutes.
The Piranha myth was born.
Fish experts however, dispute his claims as it would have taken a shoal of 500 starved Piranha fish to eat a cow in only a few minutes. It has since been argued that the cow might have been very small or young to have been eaten by the fish in only two minutes.
Attacks on a mammal and the stripping of flesh to the bone might not possibly occur as most carcasses of animals washed ashore indicate they still have muscle mass on them.
Essentially they still contain flesh, even when they have been bitten by Piranha fish.
Even human bodies have washed up that are not completely eaten.
Piranhas, the real ones, are said to attack only when they feel highly threatened or highly hungry. This is when they become more aggressive.
South American swimmers have succeeded swimming in Piranha-infested waters without losing an ounce of flesh. For fishermen, untangling a Piranha from the net or hooks is quite some job, because they bite once, but go for toes and feet.
Piranhas are attracted to noise, splashing, and spilling of food, fish or blood into the water. Piranhas mistake the noise of splashing with the noise of food falling, and can be thus harmful. Also, Piranhas can smell a drop of blood in 200 liters of water.
Human attacks by Piranha fish are so rare that they are not mentioned really. There are a lot of incidences where humans are attacked but not as a sustained attack to kill. More of a warning bite.
The much fabled Piranha attack is normally reserved for a school of fish, hungry because of conditions and a large dead mammal in the water.
This is why they scenario can be artificially induced, but rarely happens in real life.
Attacks on people are not likely to happen, unless you appear weak, threatening, incapacitated, unconscious or vulnerable to the Piranha fish.