The world's third-largest land mammal after the African and Asian elephants, the common hippo is no pushover. Reaching up to 5m long and weighing a mighty 4500kg (about six times the mass of a typical dairy cow), it is a huge animal that only the boldest predator would dare approach.
In addition, the hippos is amphibious, spending most of its life in rivers and lakes where it is safe from most terrestrial carnivores. It also tends to gather in large groups, meaning there are are always many sets of eyes looking out for danger.
And finally, if the hippo is attacked, it can defend itself by opening its huge mouth almost 180° and chomping on an enemy with the largest canine teeth of any land mammal, reaching over 50cm (and in extreme cases over 1m) in length.
There are between 120000-150000 hippos in Africa, with 2000-3000 belonging to the smaller species, the pygmy hippo. They are exclusively herbivorous – only plants need fear them, or so you'd think.
But the hippo is responsible for 500-1000 human deaths every year, usually people traveling in small boats through hippo territories. It's thought that the hippos mistake the boats for crocodiles, which they fear and often attack on sight. This death toll makes hippos among the most dangerous large animals on earth.
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But what animals can attack and kill a hippo?
Crocodiles
Although being aquatic keeps hippos safe from most large terrestrial predators, they do come into conflict with crocodiles, notably the Nile crocodile. A group of hippos will drive off a crocodile aggressively whenever they see one.
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But the crocs are adept stealth hunters and a hippo represents a fantastic meal so they will lie in wait to ambush young hippos, seizing the larger animal in its jaws and drowning it. There are stories of a much photographed exceptionally large (c950kg) Nile crocodile called Gustave on the Ruzizi River in Burundi who was reputed to have killed 50-200 people and also killed adult hippos.
Lions
Though an individual lion may weigh 10 times less than a hippo, lions do occasionally attack and kill hippos. This only occurs if the hippo has strayed far from the safety of water in search of grazing – and only when the lions are desperate. Even so, it takes a full pride of lionesses to take down and kill a single hippo. The first job is to keep it from retreating to water.
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Then, through a series of attacks from the flanks and behind, the lions nip in and weaken the hippo, sometimes leaping onto its back to tire it out. But it is exceptionally hazardous for the lions. A mistimed attack and the hippo could trample, bite or crush a lion easily.
Hyenas
Working in a gang, spotted hyenas will attempt to isolate a mother and its young from the hippos herd. Through constant noisy harassment and feinted attacks, the hyenas might be lucky enough to then separate the youngster long enough to kill it. They then need to drive off the mother so they can feast. But this happens rarely – there is easier prey for hyenas.
Rhinos
Like hippos, rhinos are herbivores and so there is no direct threat to either species from another. However, conflicts are occasionally reported between these two similarly sized animals. Hippos might drive a rhino from a favourite watery habitat.
Similarly, rhinos can be extremely aggressive when defending themselves or their young from perceived threats and there have been records of rhinos goring hippos to death with their horns. But this is exceedingly rare and both species will avoid bloodshed where possible.
Elephants
Similarly to rhinos, elephants are herbivores but can be aggressive and there are some records of heated exchanges between them and hippos at water holes, especially if the waterhole is dwindling in the dry season.
A large male African elephant weighs two to three times more than a hippo so the latter usually retreats in quick order back into the water should things get serious.
Humans
If hippos kill several hundred people a year, many more hippos are killed by human hunters for food. Sometimes this by indigenous people for subsistence but there is also a thriving black market for wild animal meat known as 'bush meat' supplied from professional poachers (the taste has been described as 'beefy' but 'sweeter'). Hippos are also culled if they are seen to be a danger to people.
