Over the years, behavioral scientists have repeatedly attempted to understand, define and explain tool usage by different animal species. However, given the complexities involved in data collection, it has remained an elusive and somewhat difficult to quantify task. Initially people believe that developing tools for different activities such as transportation, food gathering or for defense was what inherently differentiated ‘humans’ from animals .
This is because crafting tools for improved productivity and to make daily tasks easier and simpler to perform, required a certain level of intelligence and maturity of thought that scientists believed animals did not possess. The goal of the research paper is to review and compile the various exiting definitions of tool use amongst animals and to develop an understanding of how these definitions have evolved with more in-depth research studies in the field.
In order to accomplish this objective, the paper will explore how different species of ants started to use tools, the kinds of tools that were employed, the purposes for which these ant species used them, and then develop a comparative analysis with how other animal species, namely insects and chimpanzees engage in tool use .
This will not only help create a link between the factors that determine tool usage in various species, but will also present future research possibilities into how the level of ecological cognition in animals determines the nature and extent of tool use in the animal world. This correlation between animal intelligence and tool usage will also, to a large degree, explain the evolution of the different species.
And lastly, the paper will also present as definitive a picture as possible of the particular tools that are used by ants, the geographical locations where these ant colonies exist or used to exist, and in what way, if any, have ants modified, reduced or increased tool use to serve different purposes.
Animal Tool Use: A Theoretical Framework
Observing any animal employing a tool of any sort raises certain crucial questions about the underlying behavioral differences between human beings and animals. Long believed to be an activity reserved for the superior intelligence and evolutionary development of mankind, an increasing body of research and evidence emerging that has established beyond a doubt that animals have been using tools in form or another for different activities since a long time .
This in turn raises several research questions:
Are animals aware of how the tool works and is there a conscious and planned thinking process after which the tool use begins or was it just a fluke?
Do animals possess the level of cognitive development, like humans, that enabled them to anticipate their need for a tool, and then create and refine it?
What are the various tasks for which animals employ tools, and do all species have a history of tool usage?
What are the biological factors that differentiate the animal species that engage in tool usage and those that have no recorded history of it?
And lastly, how does this understanding of animals possessing a ‘tool culture’ impact the way comparisons are made between the cognitive capabilities of animals and human beings?
Prior to analyzing the exact nature of tool use by animals, it is important to develop an understanding of how ‘tools’ have been defined in the past by scientists and behavioral researches studying both human and animal behavior.
In 1973, Kamil and Shamsi formulated a basic working explanation for what constitutes tool use:
"The use of physical objects other than the animal's own body or appendages as a means to extend the physical influence realized by the animal" .
However, Beck’s original definition of tool use that he presented in 1980, with certain modifications over the years however, is in my opinion the most comprehensive of all. According to Beck, tool use was,
"The external employment of an unattached or manipulable attached environmental object to alter more efficiently the form, position, or condition of another object, another organism, or the user itself, when the user holds and directly manipulates the tool during or prior to use and is responsible for the proper and effective orientation of the tool” .
Depending on the degree of alterations, modifications and the manner in which tools are used by animals, determines the different classifications of tool usage.
Proto-tools are the ones that are not directly held by animals in any way. This would include the objects that a bowerbird collects and places in the nest, or how bread is sometimes used as bait to attract prey .
The other category is that of meta-tools, objects that are used by animals to acquire different things that help them in various activities. For instance, crows often search for smaller objects that help them reach longer ones, which in turn help them in getting access to food and water that would be inaccessible otherwise.
Tool Use in Ant Species
Now that a basic working definition has been established of what a tool is and thereby, which animal actions can be classified as those in which tools are deliberately employed on an ongoing basis, this section of the paper will focus on studying tool use in different ant species. Ants are unique when it comes to animals using tools, because unlike other animals that use objects, ants also use other ants in their colony to accomplish tasks. Since ants are classified as social animals, because they establish colonies and have a social hierarchy with different roles and responsibilities assigned to different colony members (there is a queen ant, soldier ants, etc.), the tools used by ant species are described as ‘social tools’, in which physical objects as well as other ants are used to help perform different tasks .
If a group of ants have to cross over a body of water, one group of ants band together and create a bridge over which the remaining members can cross over. Such behavior is unique to the ant species alone since in no other animal group is this level of unity and co-dependence observed.
In addition to this, there are various other ways in which tools are utilized by the ant community. It is important to understand that there are countless species of ants, and each category employs tools of different types for different purposes.
Weaver ants are commonly referred to as green ants belong to the Formicidae ant family from the genus Oecophylla. Their colonies, which are extensive and typically comprise millions of ants are usually found in Southeast Asia, Sri Lanka as well as a few northern parts of Australia. Weaver ants have long been studied for their rare behavior of nest building in which the worker ants weave leaves together using a sticky silk substance that is secreted by their own larvae . Their infants therefore, are used as a means of banding together the leaves by moving them forwards and backwards between leaves. Interestingly, the adult worker ants communicate with the larvae via their antennae in order to give instructions about when the silky glue should be secreted and how much.
The Dorymyrmex bicolor ant species that belong to the Dolichoderinae subfamily are mostly found in the arid, southern states of the United States. The tool usage that has been observed in these species is a classic example of how human beings compete for fight each other for access to food resources .
Since the bicolor species do not have the ability to sting as a means of self-protection and/or attack, they employ a tool strategy of throwing small rocks, stones and pebbles at the nests of other ant species living within or close to their habitat. This behavior of using sharp objects to destroy others’ nests is done so as to prevent other species to take over their food and sustenance resources, as well as to limit their population growth. Typically, bicolor ants wage this battle against the Myrmecocystus genus of ants .
The Aphaenogaster species of ants that can be found in almost any country in the world, except those located between Southern Africa and South America, use any debris they can find, from pieces of paper to wood to mud and small stones to cover up any liquid source they are in proximity to .
It took animal behavior researchers and scientists a while to understand the rationale behind these actions, which on the surface appear to be a mindless contamination of a food source. However, closer observation and deeper understanding of the biology of Aphaenogaster ants revealed that the species do so as a means of foraging for food. The easy-to-carry objects that these ants drop in liquid sources is a means are then carried back to their colonies and nests and stored as a food supply or given to the colony members for their sustenance .
The reason why this explanation has gained credibility with sociological researches is that since Aphaenogaster ants are not physically capable of engaging in trophallaxis – the process by which solid, semi-solid and liquid foods are transferred within ant colonies, either through mouth-to-mouth or anus-to-mouth exchanges – soaking objects in a liquid food source allows them to carry back large volumes of nutrition back to the remainder of their colony members.
A second – though less plausible and studied – hypothesis that has been presented to explain this behavior is self-preservation and survival. Since all ants can drown in open liquid sources, covering them with objects removes this threat to their survival .
The most interesting species of ants in terms of tool usage, in my opinion, are the leaf cutter ants that trace their roots to the genera Atta and Acromyrmex genras. These ants thrive and procreate in tropical climates and are found in abundance in Central and Southern America, Mexico as well as some parts of southern United States . What makes these species particularly interesting is the fungus-growing culture they live in, which has led sociologists and animal researchers to classify them as the most multi-layered living species after human beings.
Leafcutter ant colonies are built on the principle of ant-fungus mutualism. Basically, the ants grow different kinds of fungi (which is their primary food source) and in order to do so, they cut through all kinds of fresh vegetation from flowers to leaves and grasses and even weeds . These freshly cut plant material is then fed to their fungi, and the worker ants in the colony are also designated the task of ensuring that the fungi stays healthy and protected from molds and pests. They do so with the help of a bacterium that grows on their skin and is excreted onto the fungi to protect it from pest attacks of all kinds. These fungi are not grown in isolation but in fact take the shape of very elaborate fungi gardens. The tools employed in carrying the plant materials that act as feed for their fungi cultivations, include large leaves that are carried by columns of ants on top of which the ‘fungi food’ is carried . Since carrying away waste from their colonies immediately is also important (otherwise the heaps of excrements attract bacteria and viruses that damage their fungi garden), the ants first gather waste from all nests using sticks that act as shovels and once the collection has been done, they are carried away from their nests and buried.
Conclusion
While birds and other mammals fashion different objects to serve as tools, the ant species is unique in that they make use of each other’s bodies, and even those of their larvae for crossing dangerous terrains, building nests, and even for transporting food from the source back to their homes. In addition to the social nature of tool use, there is also an unexpected level of innovation in terms of how ants make use of whatever objects are available in their surroundings to fulfill their needs and the level of sophistication they bring into it.
Maps and Figures
Figure 1: World Distribution of Weaver Ants Oecophylla longinoda
Oecophylla smaragdina
Fossil records of Oecophylla
Figure 2: Distribution on leafcutter ants in Texas
Figure 3: World distribution of leafcutter ants
Figure 4: Development of a fungi garden by leafcutter ants
A: Leafcutter ants cutting through leaves
B: A fungi gardenC: Lifecycle from workers, soldiers to queen
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