Hippopotamus, facts and photos (2024)

What is a hippo?

Hippopotamuses are large, semiaquatic mammals native to sub-Saharan Africa. Although their name comes from the Greek for “river horse”—because of the time they spend in the water—their closest living relatives are whales, dolphins, and pigs. They can’t swim, breathe underwater, or even float—but they have developed a tactic that lets them nap underwater.

(Learn about the surprising ways that animals sleep.)

These huge herbivores are known for their enormous teeth, aggressive nature, and the myth that they sweat blood. Here’s what you need to know about one of Africa’s most dangerous animals.

Appearance

Hippos are the world’s third-largest land mammals after elephants and white rhinos. Males can reach lengths of 10.8 to 16.5 feet, and weigh up to 9,920 pounds, while females weigh up to 3,000 pounds.

These muscular animals have round torsos and pinkish brown bodies with two-inch-thick, waterproof skin, and short, stout legs. They might not look aerodynamic, but hippos can reach speeds of up to 22 miles per hour on land over short distances.

Hippos have impressive teeth inside their huge mouths. Their molars are used for eating while their long, sharp canines—which can reach 20 inches—are for fighting. Their remarkably strong jaws can open to 180 degrees and their bite is nearly three times stronger than a lion’s. One bite from a hippo can cut a human body in half.

Life in the water

Hippos live in waterways such as rivers, lakes, and mangroves. Their skin may be thick but it is extremely sensitive and can easily burn or dry out in the fierce African sun. So, they spend most of their day in the water or mud to keep cool, wet, and protect their delicate skin.

When basking on the shore, they secrete an oily red sweat-like substance that moistens their skin, repels water, and protects them from the sun and germs. This reddish liquid is behind the myth that hippos sweat blood.

Hippos cannot swim or breathe underwater, and unlike most mammals they are so dense that they cannot float. Instead, they walk or run along the bottom of the riverbed. Because their eyes and nostrils are located on the top of their heads, they can still see and breathe while underwater. When totally submerged, the ears and nostrils shut tight to keep the water out, and hippos can hold their breath for five minutes.

Hippos often nap in the water during the daytime. A subconscious reflex allows them to push themselves to the surface to breathe without waking up so they can sleep without drowning. At sunset, they leave the water to graze, eating up to 110 pounds of grass each night.

Aggression and dominance

These social animals live in groups called herds or pods, which typically include around 40 individuals or as many 200. They are highly territorial, and use dung middens—an area where they repeatedly poop—to mark their territory and communicate with other hippos. Males will use their tail to flick their dung in all directions as a display of dominance.

Although hippos are vegetarian, they can be aggressive when they sense danger—such as when something, or someone, encroaches on their habitat—and their deadly strength makes them one of Africa’s most dangerous animals. The likelihood you will diein a hippo encounter (86.7 percent) is higher than that of lions (75 percent) and sharks (25 percent). While the number of human deaths from hippos is unknown, it could be as many as 500 to 3,000 each year.

Reproduction

Females reach sexual maturity around the age of 10. Gestation lasts eight months, and they give birth to one calf every two years. Hippos mate and give birth in the water.

Weighing nearly a hundred pounds at birth, newborn hippos can hold their breath for 90 seconds. Once mother and calf have bonded, they join schools of other hippos for protection against predators. The calf stays with its mother until around seven years old.

Threats to survival

The International Union for Conservation of Nature classifies hippos as vulnerable to extinction. Although the hippopotamus doesn’t have many predators, it is threatened by poaching for its meat, fat, and ivory teeth. Other threats include the loss of its habitat and human-hippo conflicts. Because the species is slow to reproduce, threats can significantly impact population numbers.

The only other living hippo species, the pygmy hippo, is an endangered species native to West Africa.

(Human-hippo conflicts are exploding in this pristine patch of Kenya.)

As ecosystem engineers—a species whose presence changes, creates, destroys, or maintains a habitat—the loss of hippos also affects the wider ecosystem. When hippos defecate in the water during the daytime, their dung—which is rich in nutrients—washes through the waterways and delivers important elements like nitrogen and phosphorus to other species in the ecosystem.

Human impacts can interfere with this important cycle. If rivers do not flow—due to climate change or human developments—the hippos’ nutrient-rich dung cannot be circulated through the ecosystem, and aquatic animals and plants suffer. In the areas where the waste then builds up, it can reach such a high concentration that most species cannot survive the resulting high levels of algae and low levels of oxygen.

The once-healthy population of hippos in Virunga National Park in Democratic Republic of the Congo—which was around 29,000 in the 1970s—was devastated by poachers until there were fewer than 900 remaining in 2005. Thanks to better enforcement and conservation initiatives, the Virunga population has started to recover, and hippo populations around the world are currently stable.

Editor's note: This story was originally published on March 10, 2011. It has been updated.