Tool use (zoology)

A tool is considered something which is not an integral part of an animal’s body but is used by the animal to accomplish a specific task. For example, a lobster may use its claw to crack open shells, but since the claw is a normal appendage of the lobster, it is not considered a tool. When humans use a similar object, a nutcracker, to open shells, the nutcracker serves as a tool. It is difficult to define tools accurately. Examples of tools acceptable under the definition of one scientist may not meet the criteria of another investigator. Some scientists expand the definition of tool use to include specialized structures some animals use to extend their capability to locate and capture prey. These capabilities might include echolocation or sonar, electromagnetic fields, and specialized cells used for feeding, such as the cnidocytes used by jellyfish. Other scientists consider products produced by an organism to be used to capture food as tools. Under this definition, a spider’s web is considered a tool.

Quite often, objects taken directly from the environment, such as stones or sticks, are used as tools without further modification by the animal. Other times, the object may be modified by actions such as stripping the leaves from a stick prior to use. Tools allow the user to complete a task more easily or to accomplish a task that may not have been possible without the advantage provided by the tool. The size, shape, and even texture of tools vary across the animal kingdom. Some animals use trees as tools and others use grains of sand. Some fish use spurts of water as tools. In addition to capturing or obtaining food, tools are also used in grooming, for defense, or even as protection from the elements. Thus, animals that use tools are actively interacting with and even modifying their environment.

Tools from Nature

Many different species of animals, including insects, fish, birds, mammals, and primates, are known to use tools in some way during their everyday activities. While many different types of tools are used in the animal kingdom, the stick is a common and readily available tool. The use of sticks as tools has been well documented in nonhuman primates, such as chimpanzees, apes, and orangutans. Primates often use insight to solve a problem using tools and the young learn to use tools from either observing or being taught by the adults. A classic example of insight learning leading to multiple tool use in chimpanzees was shown by Wolfgang Köhler, an early twentieth century psychologist. Chimpanzees held in captivity were offered food that had been placed beyond their normal reach. When boxes and sticks were added in the enclosure, the chimpanzees stacked the boxes, climbed them, and then used the sticks to knock down bananas that were hanging overhead. If one stick was not long enough, they would connect them together.

Orangutans and chimpanzees strip the leaves from a stick and use it to probe into the nest of insects such as ants or termites. When the stick is removed from the nest, the insects crawling over it can be eaten. Leaves themselves have been used by chimpanzees to gather water for drinking. Birds, too, use sticks to probe for insects and to remove them from crevices in the bark of trees. Some birds, the Galápagos woodpecker finch for example, will use their bill to trim and modify the twig before using it as a probe. Pacific island crows use their beaks to modify sticks as well as leaves before using them as probes. In the absence of sticks or leaves, some animals will use cactus spines as probes. Elephants use trees and sticks in various ways. They will rub against a tree, or they may pick up a stick with their trunk to scratch. They have been observed to use tree trunks as levers and to use sticks to remove ectoparasites. When monkeys throw sticks and rocks, they are using these objects as tools for defense.

Stones are another common tool. Sea otters use stones in two different ways. Some otters will carry stones with them when they dive and use the stone as a hammer to free a tightly adhered abalone from a rock. While floating along the surface on their backs, otters use stones to crack open the shells of abalone or of bivalves such as clams, mussels, or oysters, which they also pluck from under the water. Otters may use bottles floating in the water to crack shells. Birds use stones in a similar way. Egyptian vultures pick up stones in their beaks and use them in a pecking fashion, like a hammer, to crack open an ostrich egg. If this method fails, they will fly at the egg while clasping the stone in their talons. Mongooses also use rocks to crack eggs. Other birds, such as eagles, gulls, and crows, drop shelled animals, such as turtles, onto the rocks to crack their shells. Vultures are known to drop bones of prey onto rocks to crack them open and expose the marrow. Chimpanzees use stones to crack open nuts, analogous to humans using a hammer and anvil. Even spiders use stones as tools. The trap-door spider, Stanwellia nebulosa, uses a stone as a defensive tool. If forced to retreat when being attacked, the spider uses a stone to close off its burrow behind it.

Other Tools

In Japan, one species of crow uses a very different tool, a car. It has been reported that these crows use cars as nutcrackers by placing the nut on the road and, after a car has run over it, retrieving the nut meat. If the car should miss hitting the shell, the crow may try again.

Humans are not the only species to use tools for fishing. Some green herons are known to drop objects into the water to attract fish looking for food. The herons then consume the curious fish. The archer fish uses jets of water shot from its mouth to knock insects off overhanging branches and into the water. Some scientists do not view this as a tool because the water passes along a specialized region of the mouth. However, it is similar to using a bow and arrow to subdue prey from a distance. Octopuses use water shot from their siphon system as a broom to clean the exoskeletons of eaten invertebrates from its den. An octopus may also use the jet of water to modify the size of the den. Another group of animals that uses a form of liquid tool belongs to the spider family, Scytodidae. These spiders shoot sticky material from modified venom glands to entangle their prey.

Spiders use their webs as tools in various ways. Species of spiders that construct webs make them with silk produced from modified appendages called spinnerets. Webs are used to ambush animals that happen upon them. Some spiders strum their webs and use them as tools for communicating. Others may spin a long single strand of silk that they use as a drag line to find their way back or as a safety line to catch themselves. In some species, young spiders make silk parachutes which trap the air currents and allow them to be dispersed far from the nest. Spiders of the genus Mastophora spin a single thread, on the end of which is a sticky globule. By suspending the thread from one leg, the spider uses the web to “fish” for male moths, which are attracted to the sticky globule containing chemicals similar to the pheromones produced by female moths to lure males for mating.

The jellyfish and the hydra, two members of the phylum Cnidaria, have specialized cells, cnidocytes, concentrated on the surface of their tentacles. Inside these cells is an organelle, the nematocyst, which contains a thread. The nematocyst is stimulated to discharge when prey is near. This thread may have a barb on its tip that will penetrate the body surface of the prey, or it may be a lasso that wraps around the prey. The prey is then pulled into the digestive cavity of the cnidarian.

Some tool usage is specific to a region, or a certain subset of species. The female bottlenose dolphins found in Shark Bay, Australia, use a sponge as a tool to dig for prey on the seafloor. Scientists have observed that these dolphins pass this skill on to their daughters, but not onto their sons. The dolphins use the sponges live a globe over their nose to protect their face from injury and stings while rummaging on the seafloor for sandperch. Tool usage has allowed these dolphins to access a food source that is atypical for them.

Sonar

Bats and dolphins are two good examples of animals that use echolocation to locate prey. Since sound waves can travel over great distances, the prey can be well beyond the predator’s immediate area. The objects do not need to be large to be detected. Bats can locate mosquitoes. By analyzing the sound waves returning after bouncing off an object, the bat knows which objects are moving and which are stationary. The moving objects represent potential prey. Some potential prey, moths, have evolved a way to detect that they are being tracked by a bat. Thus, they are able to take evasive action and seek shelter near a stationary object such as a tree, or by landing on the ground. In a similar manner, dolphins use a series of high-frequency clicks to track fish. However, the fish, unlike the moths, are often not aware that they are being followed.

Principal Terms

Echolocation: The ability of animals to locate objects at a distance by emitting sound waves which bounce off an object and then return to the animal for analysis

Ectoparasite: A parasite, such as a tick, that lives on the external surface of the host

Ethology: The study of an animal’s behavior in its natural habitat

Insight Learning: Using past experiences to adapt and to solve new problems

Pheromone: A hormone produced by an animal and then released into the environment

Predator: An organism that kills and eats another organism, generally of a different species

Primates: A group of mammals including apes, chimpanzees, monkeys, humans, lemurs, and tarsiers

Bibliography

McGrew, W. C. Chimpanzee Material Culture: Implications for Human Evolution. Cambridge UP, 1992.

Maier, Richard. Comparative Animal Behavior: An Evolutionary and Ecological Approach. Allyn & Bacon, 1998.

Rubenstein, Dustin R., and John Alcock. Animal Behavior. 11th ed., Oxford UP, 2019.

Sherman, Paul W., and John Alcock, editors. Exploring Animal Behavior: Readings from “American Scientist." 6th ed., Sinauer Associates, 2013.

Smith, Ellie. “The Puzzling Pattern of Tool Use in the Animal Kingdom.” The Oxford Scientist, 19 Oct. 2023, oxsci.org/tool-use-in-the-animal-kingdom/. Accessed 12 Oct. 2024.