Last night, I headed down to the beautiful Bell House, in the Gowanus section of Brooklyn, for this month's Secret Science Club lecture. This month's lecture featured my great and good friend Dr Simon Garnier, who heads up the New Jersey Institute of Technology Swarm Lab. Dr Garnier is a Renaissance man, he's a biologist whose study of ants and their behavior has led him to being a robotics expert. I arrived early to the beautiful Bell House and had an opportunity to catch up with him- he regaled me of tales of transporting his cat to Europe while on sabbatical, and other humorous slices of life from a tragic period of time. Needless to say, it was time well-spent catching up, especially since we were joined by a couple of other SSC regulars in a long-overdue reunion.
Dr Garnier's lecture topic was The Self-Assembling Horde: Building Functional Structures on the Move. Dr Garnier began his talk with a self-deprecating joke about his accent, assuring us that he was talking about the ant, an insect, rather than the aunt, that weird lady at Christmas asking you why you don't have kids.
Dr Garnier then posed the question: What is life? He noted that, as a biologist, everything he does depends on this definition. He used Emerson as an example of a poet's definition of life: The creation of a thousand forests is in one acorn. Biochemist Albert Szent-Györgyi's definition was: Life is an electron looking for a place to rest. Astrobiologist Michael Russell stated: The purpose of life is to hydrogenate carbon dioxide. Life creates entropy, resulting in more chaos.
Dr Garnier then gave us his somewhat jocular definition of life: Life is a complex, autonomous, multi-level game of Lego. He then gave us an overview of the various levels of organization: atom, molecule, macromolecule, organelle, cell, tissue, organ, organ system, organism. The self-organization of individuals through interaction results in disordered elements forming a global order. He illustrated this with an adorable video:
Things that aren't very smart bump into each other and eventually organize.
Dr Garnier concluded: self-organization plus natural selection equals life. He added that he would add another layer to the atom-to-organism self-organism, the superstructures formed by some organisms, such as social insects. He displayed several examples of such superstructures as fire ant rafts:
And clusters formed by honeybees to ward off the attacks of wasps and hornets:
Dr Garnier then narrowed his focus to army ants of the genus Eciton. Army ants are not defined taxonomically, but by behavior- they are nomadic, form new colonies by fission, they have strict reproductive cycles, and they are very carnivorous, being top predators equivalent to lions ecologically. Dr Garnier noted that they are very strange ants. The genus Eciton is completely blind. Eciton forms colonies of up to a million individuals- Dr Garnier compared the movement of a large colony to the inhabitants of Philadelphia packing up and moving thirty kilometers every day. When the ants stop moving, they form living bivouacs in which they shelter the queen and her brood.
Being nomadic, army ants cannot engineer the environment like ants that build nests. Ants such as leafcutter ants build elaborate nests, and use the leaves they harvest to grow gardens of the fungus that they feed on. Colonies of up to twenty-five million ants form highways along which they transport leaves:
Army ants such as Eciton, being constantly on the move, do not build infrastructure- they inhabit a chaotic environment which cannot be engineered due to time constraints. The ants have evolved behavioral and anatomical adaptions to attach to each other to build structures on the fly. These structures are self-repairing.
The NJIT Swarm Lab has studied the ants, which do not thrive in laboratory settings, in the field for over ten years. Dr Garnier broke down the study of on-the-fly construction of superstructures as a function of achieving three objectives: overcoming constraints on movement, maintaining traffic along a pheromone trail, and traversing dynamic/unstable substrates.
Why do ants build where they build? They build where it is difficult to move. In a recent experiment, a board was placed as an obstacle interfering with an army ant column- the angle of the board to the ground was changed in order to make scaling it more difficult. The difficulty was measured by the number of ants which fell off the board. As the angle of the board got steeper, and more ants fell off, the ants would attach to each other to form scaffolding. Dr Garnier made the analogy of human rock climbers using each others' bodies instead of pitons to climb a cliff face. As scaling the board became more difficult, more ants would join the scaffold.
The decision whether to move or to join the structure depends on the constraint on movement- more difficulty in movement means that more ants join the structure. Dr Garnier likened the decision making process of an ant to that of a thermostat. Ants build until a structure gains maximum efficiency. Simple behaviors suffice to build complex structures- in the case of constraints on movement, if it is difficult to walk, the ant stops and helps others to overcome the constraint.
Traffic occurs along trails. In a 2012 experiment, natural bridges formed by ants were destroyed using tweezers, and the ants repaired these bridges within thirty seconds. If traffic is disrupted, it is restored using packing functions- ants crowd in to complete structures. As structures near completion, fewer ants crowd in. How long does an ant stay in a structure? This is a function of traffic, as long as traffic is high, and and would stay indefinitely, but as traffic lessens, an ant will move itself. Dr Garnier proposed and analogous situation in which human commuters assembled the George Washington Bridge every morning at 7AM, then dissolved it at 9AM, then reassembled it at 4PM and kept it up until 7PM. He joked that this is the way it should be: "We don't want you in Jersey." He followed this up by noting the time the governor did exactly that. Dr Garnier proposed an army ant lesson: YOUR WORK IS NOT DONE UNTIL EVERYONE HAS GONE.
Dr Garnier noted that, besides the reproductive queen and male drones, there are four Eciton castes:tiny non-reproductive females whose role is largely unknown, typical food-gathering workers, long-legged workers which transport food, and long-mandibled soldiers which defend the food source by biting. Army ant colonies are parasitized by various birds which steal food from the ants, a case in which the parasites are larger than their hosts.
He then described the way in which ants build bridges to form shortcuts, displaying a video of the process:
Note that the bridge 'moves' to improve the shortcut, and the bridge is longer than an ant's body size. There is a cost/benefit analysis at work- the cost of building the bridge should not exceed the cost of moving the unspanned distance. Dr Garnier noted that there are mathematical models about this tradeoff which can predict where a bridge will be built. He gave us another army ant lesson: SOME CORNERS, IT SEEMS, ARE WORTH CUTTING. Up to twenty percent of the colony can be used to build bridges.
Ants move along a dynamic substrate... the surfaces on which ants move can be unstable, the weight of the ants atop it can move it. How do these blind ants build on changing substrates? In one experiment, the gap which had to be bridged was increased:
Army ants use hysteresis to stabilize control of constructions. Hysteresis is a delay between cause and effect upon change in the direction of a cause. As a bridge nears a stable state, the probability of ants leaving or staying is about equal. After a stable state is achieved, the probability of ants leaving becomes lower than the probability of ants joining. This asymmetry creates hysteresis.
Hysteresis stabilizes complex structures. Traffic varies a lot, but hysteresis prevents overreaction to variations in traffic, and creates bridges which do not collapse and are not overlarge.
It's here where I note that, appropriately for a Swarm Lab, a gaggle of Dr Garnier's grad students were in attendance at the lecture. From time-to-time, Dr Garnier would call out to one of his colleagues for a clarification of a mathematical model, or a clarification on a project to vacuum up an entire bivouac. In our conversation prior to the lecture, he noted that he did not like remote teaching or lecturing, and it was mostly due to the lack of feedback from both audience and colleagues.
Dr Garnier then mentioned the lack of funding for the sciences, and noted that one way he was able to get a National Science Foundation grant was to partner with Northwestern University's engineering department to create robots which can assemble themselves into structures by melting and melding together in any configuration. Dr Garnier quipped: "Your money at work!"
No additional parts are needed. Ant models can be used as models for building auto self-assembling robots.
Dr Garnier ended his lecture by urging us to support science education, noting that we are living in a time in which book burnings are occurring and women's bodily autonomy is being attacked. He noted that we may not be the resistance yet, but we very well might be.
The lecture was followed by a Q&A session. Before the first question, Dr Garnier jokingly warned the audience that living in Jersey had destroyed his French but had not improved his English, so they might have to ask for clarification. The first question involved the last ant forming a bridge- Dr Garnier joked that she was able to safely cross an obstacle: "Don't worry about her." Regarding colony sizes, they range from about ten thousand (recently 'fissioned off colonies') to about a million- smaller colonies use shorter trails with fewer bridges? Which caste is the most important in bridge construction? It's unknown at this time. Soldier ants, about 2% of a colony, are not involved- they only bite, and cannot even feed themselves due to the size of their mandibles. Do other ants form bridges? Weaver ants in Australia form bridges, but these are a function of other ants walking over them- in contrast to Eciton army ants, weaver ants have excellent vision and stop at gaps. Weaver ants can see if an impasse is unbridgeable. Blind army ants just find another route if a gap proves insurmountable.
Why did ants evolve social behavior? The prevailing theory is because the workers are the offspring of diploid queens and haploid males who develop from unfertilized ova, therefore each of these ants shares 75% of its genome with its sisters, while it would share 50% of its genome with any offspring. It's an indirect passing of genes, inclusive 'fitness'. In other organisms, social behavior may result from more 'selfish' behaviors- a fish in a school might hide behind other individuals, or otherwise avoid predators.
Why are army ants nomadic? Army ants are weird ants. They have a strange reproductive cycle in which many larvae are produced at once, which necessitates the consumption of a lot of protein. The ants need to move so they don't exhaust the resources in a constrained area- its a case of move or starve. Are army ants cannibalistic? This hasn't been observed, but some ants lay eggs as a food resource. Why are they blind? They re-emerged after living underground.
Are their atypical ants? Outliers? One study of ant foraging behavior noted that ants wander around in search of food sources, the trails are more varied in environments with patchy resources, and are less varied when adequate food sources are found.
How about castes? Eciton has four observed non-reproductive castes, but some leafcutter ants have 13 castes, the smallest of which can perch on the heads of the largest. The smallest leafcutter ants tend the fungus gardens that the ants subsist on. Regarding intelligence, a typical ant has about 12,000 neurons, they don't know much.
Regarding field work, the main difficulties are finding the ants and making them walk your setup. As far as the energy it takes to make bridges, the exoskeletons of the ants can lock into position, so it requires little energy to sustain weight.
Asked about a particularly weird study, Dr Garnier noted that he was approached by a law enforcement agency about a crime prediction project- looking at data, can criminals be likened to an army ant swarm dependent on environmental factors? Can a model be formed of crime (e.g. drug dealing) as a collective market-based activity and used to predict where a criminal 'swarm; will hit next?
What is the purpose of bivouacs? To protect the queen and her brood. Bivouacs even provide temperature regulation, with ants shifting position in order to maintain optimal conditions for larvae. Among nest building ants, the brood is moved throughout the colony to maintain optimal temperatures.
Some Bastard in the audience asked Dr Garnier if the Swarm Lab has sent any researchers to study distantly related Old World ants which behave similarly to New World army ants. Alas, the NJIT Swarm Lab has not sent any grad students to Cameroon to study driver ants.
Once again, the Secret Science Club has served up an excellent lecture. I often talk about the 'Secret Science Sweet Spot', and Dr Garnier always hits it- he serves up interdisciplinary material, illustrated by memorable video footage, he finds ways to involve his graduate students in the lectures, and he leavens his material with humor. Suffice it to say, he consistently knocks it out of the park. Kudos to the good doctor, to Margaret and Dorian, and to the staff of the beautiful Bell House.
Now, for a taste of that Secret Science Club magic, here is Dr Garnier lecturing on the self-assembling horde:
Pour yourself a nice beverage and soak in that SCIENCE!!!