A favorite subject for nature documentaries, the hippopotamus is huge, heavy and herbivorous. Hippos are the third largest terrestrial animal – only elephants and white rhinos are bigger – and surprisingly agile in an aquatic environment. But don’t be shy about a hippo: they are extremely aggressive and kill around 500 people per year, making them the world’s deadliest mammals (after humans). Here are some more unexpected facts about hippos.

1. There are two species of hippos.

Both species are classified in the Hippopotamidae family, but belong to two genera. The Nile familiar or common hippopotamus, Amphibious hippopotamus, is more abundant and can be found in aquatic habitats across sub-Saharan Africa. The smallest pygmy hippopotamus, Choeropsis liberiensis, number less than 2,500 individuals in the wild and is considered endangered. They live in the tropical forests of Sierra Leone, Liberia and Côte d’Ivoire.

2. Whales and dolphins are the closest relatives of the hippo.

Despite their name, derived from the Greek for “river horse,” hippos are not related to horses. Hippos belong to the order Artiodactyla, which includes equal-toed ungulates like pigs, camels, and deer, as well as cetaceans (whales, dolphins, and porpoises). Hippos and whales had a common ancestor who lived about 55 million years ago, after which hippos and cetaceans branched out. Hippos still today share many characteristics in cetaceans, such as almost hairless skin and underwater birth. Scientists have even discovered that hippos make clicks moving underwater, similar to a cetacean echolocation.

3. Hippos are built for water.

With their round bodies, large heads and small legs, hippos are basically shaped like a submarine. They spend most of their time resting in lakes, rivers and wetlands. At night, they emerge on the earth and graze on grasses and reeds, creating “hippo paths”Through the vegetation to their favorite spots. They even mate and give birth when submerged.

4. Hippos cannot swim.

Surprisingly, these semi-aquatic animals cannot swim. They have dense bones that cause them to sink in deep water, but are great for walking, galloping, or bouncing in shallow rivers and lakes. Their bones provide just the right amount of weight to achieve optimal levels buoyancy, effectively transforming the river into a microgravity environment. Hippos can be deceptively fast as they move underwater and on land, where they can run at up to 24 mph.

5. Fish help hippos keep their skin clean.

Hippos and fish have a symbiotic relationship in their aquatic habitat. African fish, including cichlids and barbels, nibble on dead skin, algae, and parasites on the hippo’s skin and inside its mouth. The fish eat this crud as a food source while removing potentially harmful pathogens from the hippo’s body. Fiona, the famous hippo from the Cincinnati Zoo, enjoys these thermal cures tilapia in its enclosure.

6. The red “sweat” of hippos is actually sunscreen.

Hippos are often coated in pink “sweat“, which is not actually sweat or blood. They secrete two substances that turn red (hipposudoric acid) and orange (norhipposudoric acid) and act as sun filters. The pigments also have antibacterial properties. against Pseudomonas and Klebsiella, which can cause infections.

7. Hippos are so dangerous that Nile crocodiles avoid them.

Hippos are Africa’s deadliest mammal, even more dangerous to humans than lions or elephants. Their victims are often fishermen or boaters, which they load underwater. Hippos overturn boats, trample and drag people into lakes, and bite with incredible force. They can amputate limbs, fracture bones and mutilate soft tissue. In 2014, 13 people in Niger deceased when a hippo overturned his boat, and in 2018, a hippo attack an American woman on a safari in Zimbabwe after overturning her canoe. (She survived with a broken leg.)

8. People have been hunting hippos for hundreds of thousands of years.

Homo sapiens and our ancestors hunted hippos as a source of meat and bone to make tools. One of the oldest known bone hand axes is 1.4 million years and made from a hippopotamus femur. Hippopotamus meat has been an important source of human food since the dawn of homo erectus. Archaeologists investigating a 700,000-year-old human habitation site in Ethiopia have found numerous hippo bones that bother traces of butcher’s tools. Other archaeologists working in Kenya’s Turkana Basin have found a similar disarticulated hippo BONE bearing butchery marks in a human habitation 1.9 million years old.

The ancient Egyptians hunted hippos for their meat, skin and teeth, and engraved patterns of spiritual protection in their tusk-like canines. Because hippo ivory is denser and stronger than elephant ivory, it was a popular material for dentures in the 18th century. George Washington’s dentures had teeth carved from hippopotamus ivory, and Paul Revere is believed using hippopotamus ivory in his dental office.

9. President Calvin Coolidge received a hippo as a gift.

Coolidge received a number of potentially dangerous pets during his time in the White House, such as two named lions Office of Tax Reduction and Budget. Another was William Johnson Hippopotamus, aka Billy, a pygmy hippo from Liberia given to Coolidge in 1927 by rubber mogul Harvey Samuel Firestone.

Coolidge quickly donated Billy (and his other exotic animals) to the National Zoological Park, where a biologist associated him with a female pygmy hippo named Hannah. Billy eventually sired 18 calves, all named Gumdrop followed by the Roman numeral (I thought XVIII). It is believed that all pygmy hippos currently in American zoos are descended from Billy.

10. A congressman from Louisiana wanted to import hippos for cattle.

In 1910, the United States faced a beef shortage, and what needed to be done in the face of the crisis was dubbed “the meat issue” by the media. On March 24, 1910, a bill was introduced by Representative (later Senator) Robert Broussard of Louisiana to import hippos from Africa and introduce them to the bayous of Florida, Mississippi and Louisiana. Hippos would not only provide tons of meat, but also eat water hyacinth, an invasive species that blocked southern streams and rivers. The New York Times asked readers to think of the fatty flesh as “lake cow bacon”. Broussard’s bill failed.

11. Invasive hippos are rampant in Colombia.

Colombia is the only country outside of Africa where hippos are found in the wild. Drug lord Pablo Escobar imported a male hippo and three female hippos for his private zoo, but after his death in 1993, the hippos were left to fend for themselves. Soon these so-called “cocaine hippos” escaped, reproduced, and colonized the Magdalena River, Colombia’s main waterway. The hippos found themselves in an environment where food was plentiful, without competition and without drought. Their population has exploded.

Today, 80 to 100 hippos are rampant in Colombia, and the number is expected to grow to over 1,400 by 2034. Hippos are considered an invasive species and represent a major challenge for the Colombian government. Environmentalists predict that the animals will cause environmental damage such as altering the chemistry of rivers and removing native species like manatees and otters, but so far public opinion is with hippos.