Humans are grimly adept at making tools that can kill things, but elsewhere in the animal kingdom, other species also make tools to use for killing. On rare occasions, the items are directly used to inflict a fatal wound.
More commonly, however, they are used to weaken, wound or make the prey more vulnerable. Then the predator finishes the job. Here are 10 predators that kill with tools.
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Predators that kill with tools
Polar bears
Polar bears are skilled hunters, known to stalk, ambush and then pounce on their prey, but occasionally they employ a different tactic. They lift a chunk of rock or ice in the air and then hurl it at a walrus.
The practice has been documented by the Inuit hunters of the North American Arctic. In one historical account, from 1824, a polar bear dropped a lump of ice on the head of a sleeping walrus, killing it instantly.
In another, from the nineties, an experienced Greenlandic hunter saw the aftermath of an attack, when he stumbled across a freshly killed carcass. The polar bear had fled, but the walrus lay next to a large piece of ice that had obviously been used to bash its head in. Polar bear urine and claw marks confirmed that the predator had been there.
Although the practice is thought to be rare, this sophisticated form of tool use shows how smart polar bears are. The skulls of walruses are too thick for polar bears to easily crush, so the resourceful animals have found another way.
Chimpanzees
Chimpanzees eat a varied diet, with lots of fruit, leaves, nuts and seeds, but from time to time they also hunt small animals, such as monkeys and antelopes.
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In the Fongoli region of Senegal, chimpanzees have been observed hunting bushbabies with tools. They tear branches from trees, strip off the bark, and sharpen the ends into a point with their teeth.
Then they use the rudimentary spears, which are around 75 centimetres long, to stab bushbabies while they sleep in their nests inside hollow trees. This injures, rather than kills the bushbabies, making it easier for the chimps to then bite and kill them.
Females are more likely to hunt like this than males, probably because it’s difficult for them to chase moving prey when they have their youngsters clinging to them. The discovery also sheds light on the evolution of human hunting, because chimps are one of our closest relatives.
Burrowing owls
Just as people leave bait out to lure animals into traps, so too burrowing owls use dung to entice dung beetles to their doom.
As the name suggests, burrowing owls live in underground burrows, which they typically repurpose from mammals, such as prairie dogs and badgers. They decorate the inside of their home with assorted mammal dung, and for a long time, researchers thought this was to camouflage the scent of their vulnerable owlets.
Then a study showed that the faeces produced by birds in burrows that contain cow dung contained ten times as many dung beetles as those produce by birds from poo-free homes.
Conclusion? The owls are using dung as a tool to attract prey, which they then promptly dispatch with their beaks. This is known as a ‘bait and wait’ strategy. The owls spend a lot of time standing next to their burrows, waiting for the bait to be taken. So, it’s almost as if they are ‘fishing’ for dung beetles.
Green herons
Not to be outdone by burrowing owls, green herons also use tools to bait and wait, but they really do go fishing. The birds, which are native to North and Central America, feed on fish, frogs and other aquatic creatures which they source from their local ponds and wetlands.
In 1958, ornithologist Harvey Lovell described a green heron in Florida that dropped bits of bread into the water, and then captured the fish that came to the bread. After that, more examples were noted. Herons have been spotted using feathers, fruit, flowers, dead mayflies and spiders, bits of straw and even popcorn as bait. Once in striking distance, the heron then gobbles up the prey.
Here the tools aren’t used to kill the prey directly, but they do contribute to its death. Other bird species observed using the same strategy include great egrets, sun bitterns and pied kingfishers.
New Caledonian Crows
New Caledonian crows make and use tools to help them catch the grubs that they eat, but what sets them apart is the sophistication of these tools. Crows use a multi-step process, learned from their elders, to create complex hooks which they use to extract larvae from logs.
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To do this, they need to snip the right twig, in the right way, from the right plant. Thin, pliable stems are chosen and cut in precise places to create a barbed end. Bark is stripped away, and in a finishing flourish, the shaft of the tool is often bent into a gentle curve. This means that when a bird holds the stick facing forwards and places it in a hole, they will have the best chance of seeing what’s in there.
In a lab-based set up, crows have even been seen combining separate tools together to make better ones. This indicates that crows have exceptionally good problem solving abilities, not to mention dextrous beaks.
Sea otters
When they hold paws and float on their backs in the sea kelp, it’s hard to remember that sea otters are the apex predators of the nearshore marine world. They eat a varied diet, including sea urchins, molluscs, crustaceans and fish, all of which they must catch and kill.
There’s just one problem, however. Much of their prey is either anchored to the sea floor or protected inside a robust shell. So, the otters use tools to help them. Stones are used as hammers on the sea floor to dislodge molluscs, and as anvils at the surface to help break open shells. The otters lay on their backs, with a stone on their belly, and then smash the prey against it. If that doesn’t kill the prey outright, it is soon dispatched when the otter chomps into it.
Vultures
Vultures are primarily scavengers that feast on what they find, but some buck the trend. Egyptian vultures use stones to break open the large, robust eggs of ostriches. They pick up pebbles in their beak and repeatedly drop or throw them onto the eggs until they crack. Then they eat the nutritious yolk inside.
This is tool use and it also counts as killing because it has been observed in the wild, where the fertilised ostrich eggs contain developing embryos.
Hand-reared vultures that have never seen birds cracking eggs with stones also perform the same behaviour. This suggests that Egyptian vultures don’t need to learn the method from older birds. It is a skill they are born with, preprogrammed in their genes.
Bottlenose dolphins
The dolphins of Shark Bay, Western Australia, shell out for dinner. Literally. The smart cetaceans use conch shells as tools to help them catch and kill fish.
Dolphins chase small fish into large, empty shells, then use their beaks to bring the shells to the surface, where they shake the trapped food into their mouths – a big like snaffling the last few crisps from the bottom of the packet.
The technique, which is called ‘shelling’ was first observed amongst Indo-Pacific bottlenose dolphins during surveys conducted between 2007 and 2018. Nineteen dolphins, from three maternal lineages, performed the behaviour a total of 42 times. Young dolphins learn the trick by watching those around them and then copying the behaviour.
Humpback whales
Humpback whales use tools that are as ephemeral and fleeting as they are impressive and efficient. Working in small groups, the huge mammals manipulate the air they expel from their blowholes to create walls of bubbles called ‘bubble-nets’. They then use these transient structures to corral prey, such as krill and small fish, into tightly packed shoals, which they can lunge through and eat.
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Many animals use tools to help them hunt and kill, but few manipulate them with such precision. Humpbacks in southeast Alaska have been filmed blowing bubbles into large circular nets, which contain smaller rings inside them. The whales can also control the number of rings in the net, as well as the size and depth of the net, and the spacing between the bubbles.
Bolas spiders
The bolas spider is a type of orb-weaver spider found in warm temperate and tropical climates. It is unusual because where most spiders hunt using their webs (which can also be considered a type of tool), this one creates a little spider lasso.
The lasso is a long line of silk with a small blob of glue, called a ‘bolas’, on the end. Female bolas spiders first attract a moth by releasing a cocktail of pheromones. Then, when the prey is in striking distance, the lasso is launched to snag it. When the bolas makes contact with the moth, the glue soaks into its scales and the moth becomes stuck. The spider then reels it in and kills it with a venomous bite.
This is a specialised method of hunting, that combines chemical and physical elements. The lasso itself isn’t deadly, but it might as well be, as very few moths ever escape.
