I once heard an analogy about how ant colonies are similar to human brains: Each ant is like a neuron, seemingly mindless and impotent on its own. But, when interconnected, they form complex networks that result in emergent intelligence greater than the sum of its parts. The comparison is trying to make a concept as alien sounding as a ‘superorganism’ digestible to non-scientists. In truth, however, I find this analogy belittling to individual ants. A neuron’s function to transmit electrochemical information is singular and invariant. By contrast, every ant possesses a whole brain of its own, containing a robust behavioral toolkit that is nothing short of impressive!
Ants’ nervous systems are jam-packed with features despite being tiny. Workers, who perform the most complex tasks in the colony, are usually the smartest. Consisting of roughly 250,000 neurons, their brains absolutely pale beside the ~100,000,000,000 neurons your body is using to read this right now. Nevertheless, individual ants are very capable of interaction with their environment (see Kate’s blog post about pheromones and Fletcher’s blog post about quirky ant paths for other cool examples of how ants move). They avoid predators, communicate with others, and can even learn and remember. Where individual ant brains really shine, though, is how they navigate the world around them.
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| Figure 1. Worker ant brains (left) are even larger than soldier ant brains (right) despite body size differences in Eciton burchellii [1] |
Worker ants that are tasked with finding food must travel incredibly far to do so. These ants may wander thousands of times their own body length searching for resources in locations wholly unfamiliar to them. Distances are exacerbated by environmental obstacles that affect their routes along the way. After finding something, the ant is expected to decide if that resource is worth expending precious energy to return to, make it back to the nest it departed from, and then communicate to others that it’s found something valuable.
Even humans have difficulty executing behavioral sequences like this! How is it possible that an ant with a brain so much smaller than ours is capable of pulling it off? Scientists have been pondering this question for centuries, but a precise and universally applicable answer continues to elude us. Generally speaking, we know that individual ants can perform exploratory feats beyond what we’d expect them to be cognitively capable of because their bodies and brains are specialized for that task.
When I say some ant brains are specialized for navigating, I am not saying that individual ants create a map of the world inside their brains and are consciously aware of their position in that map. That is a very ‘human’ thing to do, and ant brains aren’t nearly large enough to perform a task that abstract. What I mean is that ant brains contain distinct modules that focus on particular aspects of navigation. Each module processes some environmental cue, and the modules are wired together. Their combined activity gives the ant a cognitive system that is first-class at wayfinding but fairly basic in other areas.
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| Ants like this Dorymyrmex elegans worker must rely on their brains to locate resources over vast distances by themselves. The colony’s survival depends on their success. Photo by Alex Wild [2] |
Ants can use a dizzying variety of environmental cues to navigate. Their brains are capable of charting paths using sun position, polarized light patterns, visual panoramas, gradient of odors, wind direction, slope, ground texture, step-counting, and more. Indeed, the list of cues ants can use for navigation is bigger than the list for humans! The features of the ant’s environment determine which cues its brain will have evolved to pay the most attention to. For instance, ants living in extremely sunny habitats are likely to have brain modules that factor things like sun position into how they navigate.
Speaking of sunny habitats, have you ever wondered how desert ants can venture far from their nests without getting lost in terrain that is flat and devoid of landmarks? R. Wehner’s (2003) research found that Cataglyphis desert ants possess remarkable path-integration systems to help them get home. They have modules in their brains that keep track of motor efference (information reminding the brain what movements have been executed), and optic flow (visual information about how fast the world is moving past the eyes). The modules communicate and integrate a path which approximates the distance traveled since the ant departed its nest. The ants can then use polarized light shifts from the sun like a compass to orient directionally, travel back the triangulated distance, and find their nest almost every time despite not being consciously ‘aware’ of their position at any point in the process!
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| Cataglyphis nodus desert ant worker on barren sands. Photo by Katya [3]. |
The system described above suits ants in featureless deserts. More lush environments beget a different set of skills. Durier et al.’s (2003) research found that wood ants can navigate dense, twisting vegetation using an innovative landmark recognition system. They have modules that activate when an image in their retina matches up with a recently encoded snapshot memory-- a way of recalling “Oh yeah, I’ve been here before”. This primitive, unconscious form of memory helps wood ants navigate by chaining recognized locations in a sequence. Though their exploratory goals are the same as desert ants, their cognitive tactics are vastly different.
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| Formica pergandei wood ant worker amidst leaf litter. Photo by Alex Wild [4] |
So, is an individual ant truly like a neuron? Not really-- lone ants perform exploratory feats that prove they are robust and versatile. Despite possessing nervous systems weighing only a fraction of a milligram, individual ants are quite competent creatures. The fact that their (already impressive) individual intelligences collate at the colony level to form a superorganism capable of modifying its environment, cultivating resources, and fighting wars only further justifies why ants are such amazing animals to study, and why they are among the most ubiquitously successful organisms the Earth has ever known.
Further Reading:
R. Wehner. 2003. “Desert ant navigation: how miniature brains solve complex tasks”. Journal of Comparative Physiology A. 189, 579–588. https://doi-org.ccl.idm.oclc.org/10.1007/s00359-003-0431-1
Sean O’Donnell, Susan Bulova, Meghan Barrett, Cristoph von Beeren. 2018. “Brain investment under colony-level selection: soldier specialization in Eciton army ants (Formicidae: Dorylinae)”. BMC Zoology 3. https://doi.org/10.1186/s40850-018-0028-3
Virginie Durier, Paul Graham, Thomas Collett. 2003. “Snapshot Memories and Landmark Guidance in Wood Ants. Current Biology. 13 (18): 1614-1618. https://doi.org/10.1016/j.cub.2003.08.024
Ofer Feinerman, Amos Korman. 2017. “Individual versus collective cognition in social insects”. J Exp Biol. 220(Pt 1): 73–82. https://dx.doi.org/10.1242%2Fjeb.143891
Media Credits:
(1) Sean O’Donnell, Susan Bulova, Meghan Barrett, Cristoph von Beeren. 2018. “Brain investment under colony-level selection: soldier specialization in Eciton army ants (Formicidae: Dorylinae)”, BMC Zoology 3. https://bmczool.biomedcentral.com/articles/10.1186/s40850-018-0028-3
(2) Photo by Alex Wild. https://www.alexanderwild.com/Ants/Taxonomic-List-of-Ant-Genera/Dorymyrmex/
(3) Photo by Katya. https://www.flickr.com/photos/katunchik/27820322210
(4) Photo by Alex Wild. https://www.alexanderwild.com/Ants/Taxonomic-List-of-Ant-Genera/Formica/i-WdK7nSB/A
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