From piranha to anaconda, from goliath bird-eater spider to mata mata, here are the top 13 creepiest animals living in fresh water.
Notorious for their sharp teeth and voracious appetites, piranhas inhabit several of the major river basins in South America. These omnivorous fish are known for their taste for meat, although attacks on human beings are quite rare, despite breathless accounts from early explorers.
Piranha [Photo by Martin Shields/Alamy]
In a historic visit to Brazil, Theodore Roosevelt famously saw a group of piranhas shredding pieces of a cow carcass in seconds. His dramatic account would color popular imagination for years, even though it was based on a manipulated spectacle in which fishermen blocked off a group of the fish and starved them beforehand.
Still, piranhas are important scavengers and predators in their native rivers, and they often resort to cannibalism if food gets scarce. It's true that local fishermen occasionally have scars from close encounters with them.
It's unknown how many species of piranhas exist, with estimates ranging from 30 to 60.
Electra the electric eel (Electrophorus electricus) demonstrates her shocking power at Ford Motor Company's "Cycle of Production" exhibit at the 1939 New York World's Fair. Despite their name, electric eels are actually a type of knifefish and are more closely related to catfish than they are to true eels. These unusual fish inhabit waterways in the Amazon and Orinoco basins of South America, where they hunt prey and defend themselves by producing powerful bursts of electricity.
Electric Eel [Photo from Bettman Archive & Corbis]
Electric eels gulp air from the surface in order to breathe. Thanks to specialized internal organs, they can produce pulses of electricity greater than 500 volts, with a current greater than one amp. That's enough to kill an adult human being.
Electric eels mostly hunt invertebrates, though adults also consume fish and small mammals. They only attack human beings if they are disturbed. They tend to live in murky, stagnate waters. Scientists have long been fascinated by the species and have probed its impressive electrical abilities.
Goliath Bird-Eater Spider
Goliath Bird-Eater Spider [Photo by John Mitchell/Getty Images]
The second largest spider in the world, the goliath bird-eater (Theraphosa blondi), is related to the tarantula. It received its fearsome name after Victorian explorers witnessed one feasting on a hummingbird.
The big spiders inhabit marshy land in the rain forests of nothern South America, where they can grow to a leg span of up to 12 inches (30 cm) and can weigh more than 6 ounces (170 grams). As with many other spiders, females may eat the males after mating. Partially as a result, males have a lifespan of 3 to 6 years, while females have a lifespan of 15 to 25 years.
Despite the spider's name, birds are not the main prey of the goliath bird-eater. They prefer to eat insects and other invertebrates, although they will occasionally eat small vertebrates. The big spiders are not generally considered dangerous to human beings, although they can bite if disturbed, leaving a wound about as painful as a wasp sting. They can also release hairs that irritate the skin.
Widely distributed across much of Africa, tiger fish are fierce predators with large, razor-sharp teeth. They often hunt in packs and occasionally eat large animals. Attacks on human beings are rare but not unheard of.
Tiger Fish [Photo by Chris Johns/National Geographic]
The two largest species are the goliath tiger fish (Hydrocynus goliath) and the Hydrocynus vittatus, which is commonly called the tiger fish. Both are prized as game fish. The goliath tiger fish, which can reach sizes up to 110 pounds (50 kg), is found in the Congo River and Lake Tanganyika. The tiger fish can weigh up to 33 pounds (15 kg) and is found in the Zambezi River system.
Nile Crocodile [Photo by Jonathan Blair/National Geographic]
A year-old Nile crocodile attempts to snap up a frog in the St. Lucia Estuary in South Africa (from the National Geographic book Visions of Earth). Also known as the common crocodile, these large reptiles are distributed across much of Africa, and they have earned their reputation as among the most ferocious, deadly animals on the planet.
Male crocs typically measure from 11.5 to 16 feet long (3.5 to 5 meters), but they have been known to exceed 18 feet (5.5 meters) in length. Individual crocodiles attack anything the same size or smaller than them. They are occasionally known to hunt in packs, in which they can take down animals as large as hippos and rhinos. Nile crocodiles occasionaly prey on human beings, with estimates ranging from several hundred to several thousand deaths a year.
The ancient Egyptians feared and revered Nile crocodiles and worked them into their mystic religions. In modern times, the big animals were heavily hunted for their leather, although recent protections have helped stabilize the population at an estimated 250,000 to 500,000.