07. Giant Freshwater Stingray



 Photograph by Fenolio Dante, Getty Images

Freshwater stingrays are known to inhabit rivers in Southeast Asia and northern Australia, where they can reach enormous proportions, measuring up to 16.5 feet (5 meters) long and up to 1,320 pounds (600 kilograms). However, very little is known about these creatures, including how many are left, and if they ever enter saltwater.

Freshwater stingrays are hard to see, because they often bury themselves in river sediments. They hunt for clams and crabs by detecting their electric impulses. There are reports of the big animals overturning boats, though they rarely attack people.

Even so, stingrays can pack a powerful punch; they have a barb at the base of their tail that contains deadly poison and a stinger as long as 15 inches (38 centimeters).

Many scientists fear that freshwater stingrays are threatened by habitat loss and pollution.

09. Candiru



  Photograph by Max Gibbs, Getty Images

Perhaps the most feared freshwater species of all, candiru are parasitic catfish in the family Trichomycteridae. These small, narrow fish normally feed on the gills of larger fish in the Amazon. However, over the past few centuries there have been reports of these creatures lodging in the urethras of men and women.

Some native peoples along the Amazon have described means of preventing such a disturbing infection, which is said to be hard to remedy, even with surgery. Protection measures are said to include tough clothing, tying off extremities with ligatures, and avoiding urination around rivers. It was long believed that urine attracted the candiru, although a recent study Candirurange.

11. Goliath Bird-Eater Spider



 Photograph 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.

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