It’s now recognized that the use of tools is widespread in animals, and the article below from Functional Ecology (pdf here, reference at bottom) notes that there are fifty examples known in insects alone. Some of these, in ants, involve using various substances like leaves or stuck-together bits of dirt to sop up sweet liquids and carry them back to the nest. The article below describes not just the use of tools, but the ability to adjust their usage to environmental conditions like the size of sand grains and the surface tension of water (an index of risk), to nosh on sweet liquids without drowning. It’s the adjustment to environmental conditions of how they use a novel “tool” (a siphon made of sand grains) that constitute the new results in the article.
The insects used were lab colonies of the imported black fire ant, Solenopsis richteri, collected in Mississippi. The colonies were put in an arena that contained grains of sand that varied in size, as well as a 1 ml of a 15% solution of sugar water in a small plastic container.
Under normal conditions, the nature of the ants’ cuticles makes them able to float atop this sugar water. But to reduce the surface tension, which produced the possibility of the ants on the solution drowning, the authors added 5 concentrations of a surfactant, up to 2%). One could then measure the foraging risk to the ants by counting the number of drowned ants. There were also four kinds of sand presented to the ants: coarse, medium, fine, and mixed. Altogether, the authors made 12 replicates of each condition (4 sand grains and 6 surfactant concentrations), giving 24 x 12 or 288 replicates.
Each replicate was left for five hours after the sugar water was placed by the sand, so you can see this is a lot of work. At the end, they weighed the sand grains used by the ants as tools, the number of ants drowned in the solution, and the weight of the ants after the experiment compared with before the ingestion, giving an idea of how much sugar water was consumed.
Here are the results in brief:
First, with no surfactants, and just sugar water, few ants drowned. As the surfactant concentration rose to 2%, more ants drowned, as their bodies could no longer keep them atop the liquid that had reduced surface tension. The more surfactant added, the more ants drowned.
Second, as surfactant was added, and ants began drowning, the ants began using their tools. At the lowest concentration of 0.05%, they pasted sand grains inside the plastic sugar-water container, which wicked the solution up to the edge where the ants could consume it without having to get close to the water.
As the surfactant concentration rose higher, to 0.1%, the ants began making what the authors call “sand structures” a sand siphon that started on the inside of the container and continued to the outside and down to the “ground” where the sand piles were available. These siphons, which wicked the sugar water out of the container to where it could be safely ingested without drowning, increasing the amount of food eaten by the ants by 8%—an appreciable increase—and also reduced the proportion of drowned ants. (The siphons could wick about half of the solution out of the containers.):
Here is a photo of the siphon structure; the caption is from the paper; the red dye, added to the sugar water, shows how the sand structure wicked the solution out of the container and onto the “ground”.
The ants, then, were able to adjust their construction of the siphon to the conditions of the solution (the authors note that reduced surface tension may be characteristic of some nectars and other sweet liquids in nature), and perhaps to the perception of the number of drowned ants. They were also able to choose sand grains that were most effective at wicking the food: the medium and coarse ones. (They showed that the wicking capacity of fine sand is lower.)
The take-home lesson: the ants can somehow assess “foraging risk” and, when it’s higher, use tools, building a big siphon out of sand grains.
Now this is not the first instance of tool use in ants, though previous descriptions seem spotty. From the paper:
Several Myrmicinae ant species have been reported to be able to use debris to collect and transport liquid food into their nests (Banschbach, Brunelle, Bartlett, Grivetti, & Yeamans, 2006; Barber et al., 1989; Maák et al., 2017). There has been only one reported case of tool manufacture in ants prior to our study, but the validity of this report has not been confirmed yet. The Florida harvester ant P. badius, can construct small pellets of sand grains to soak up honey for transport (Morrill, 1972). However, this observation was only reported briefly in a short communication without any additional follow‐up study, and the data are insufficient to validate that this is a true case of tool manufacture by ants.
This, then, is a well documented case of tool use in ants—and it does count as tool use. It also shows for the first time that insects can adjust their foraging strategies to minimize risk.
Finally, the authors think it shows the ants show “high cognition”, and this is where I differ. The paper says this:
Our findings suggest that social insects may be able to create novel approaches to foraging by using available tools in situ to overcome the environmental constraints. The results also indicate that considerable capacities for high cognition and unique foraging strategy may be developed in social insects such as ants, which has previously only been characterized in vertebrates when facing risks and problems. Such sophisticated flexibility of tool use provides a powerful platform for further studying the cognitive mechanism and tool use strategy of social insects, and at the same time, promotes the research on the universality of tool use strategy in invertebrates.
Yes, it is sophisticated flexibility, though the authors don’t know whether the proportion of drowned ants, rather than the perception of surface tension (they’re correlated) leads to the construction of sand siphons.
But is it “high cognition”? Is it “cognition” at all? This isn’t a trivial question, but it’s an important one. The online Oxford English Dictionary gives two definitions of cognition related to this act (there are others):
- The action or faculty of knowing; knowledge, consciousness; acquaintance with a subject.
- Apprehension, perception
The question, then, is whether the ants are responding to an inbuilt behavioral program that robotically takes in information about the environment and responds with an adaptive act, which would accord with the second definition, or whether the ants “knowingly” do this; that is, are they conscious in some way—similar to us—of what’s going on. That would accord with the first definition of consciousness. One thing I don’t accept is that the ants learned to do this in the lab; this is surely a form of behavior that they perform in the wild. Ants aren’t that smart!
Since I’m a determinist, the ants really can’t make a conscious decision about what they do when the surface tension is low and they’re faced with drowning ants and sand grains of various size. None of us can make a free choice about what we do: we’re all constrained by our neurons and the environment we perceive. So the question here is not whether the ants make a free “choice,” but whether they are conscious of what they are doing. That is the question, and it’s one we can’t answer. All we can say is that the ants are able to perceive environmental stimuli and adjust their behavior in an adaptive way, and in this case use tools to do so. The rest involves the unanswerable question of “what is it like to be an ant?”. So it goes.
Ants adjust their tool use strategy in response to foraging risk. Funct Ecol. 2020; 00: 1– 12. https://doi.org/10.1111/1365-2435.13671, , .