Ant colonies operate without central control. This is difficult to imagine, and it’s easy to attribute control where there isn’t any.
In fact, there are many familiar systems that work beautifully without anything in charge; brains and the internet are among the many examples. No neuron tells another what to think about. In the same way, no ant gives directions or instructions to another. An ant colony consists of many sterile female workers – the ones you see walking around – and one or more reproductive females. Even though these reproductives are called “queens”, they have no power or authority. They just lay the eggs.
Regulation without central control uses simple interactions. Cells interact by jostling each other and by making chemical and electrical connections. Ants interact by means of smell – when one ant smells another with its antennae, it can assess whether the other ant is a nestmate, and what task the other ant has been doing.The pattern of interactions produces the behaviour of the whole system. A neuron uses recent experience of electrical stimuli to decide whether to fire. In the same way, an ant uses its recent experience of antennal interactions to decide what to do next.
Learning about how ants organize their collective behavior may help us to understand other systems. There are more than 14,000 species of ants, living in every terrestrial habitat on Earth. In different systems that are regulated without central control, there is a fit between a network’s environment and how it uses interactions. Interactions must regulate the system to react to the constraints set by a dynamic environment.
One: How ants deal with operating costs
One important constraint is operating costs. An example is the analogy we call “Anternet”, between the way that desert ants regulate foraging, and TCP-IP, a transmission control protocol that regulates data traffic in the internet.
Both use feedback to deal with high operating costs. Desert harvester ants have to spend water, lost when foraging in the hot sun, to get water, which they metabolise out of the seeds they collect. In the early days of the internet, operating costs were so high that it was not worthwhile to send out data if bandwidth was not available. In both systems, interaction networks avoid extra expenditure – of data transmission, or water – by staying inactive unless something positive happens. A forager does not go out unless it experiences enough interactions with ants that have found food. A data packet does not go out unless returning “acks” (acknowledgements) show that previous data packets had the bandwidth to move on.
By contrast, in the tropical forest, operating costs are low for ants. One species that lives in trees sets up circuits of ants flowing constantly from nest to nest and to food sources, in both directions. Because ants are so abundant and diverse, competition is high. Many species use resources that are also used by others. Interactions are used to generate negative feedback. The system keeps going unless something negative happens. A forager continues along the circuit unless it meets an ant of another species, in which case it is more likely to go back to the nest. An analogy with an engineered system may be a fibre-optics network that continually transmits data unless there is an interruption, or a security system that denies access only when a threshold level of incursion is reached.
Two: Ants have a nuanced security system – and no fake IDs
Another important constraint is the stability of the environment which determines how likely it is that the system can be interrupted or attacked.
Security in ant colonies, as in our own immune systems, works collectively. Ant colonies distinguish who is a nestmate and who is not using odor. There is no single odor, like a passport, that identifies all the ants in the colony. Instead, the colony odor is defined collectively by all the ants in the colony. In recent work, we suggest that each ant has its own shifting “decision boundary” to distinguish the smell of nestmates from other odors. Early in its life, it works inside the nest and encounters only nestmates, but later, while foraging, it may meet an ant from another colony and have an aggressive encounter, and place that other ant on the foreign side of its decision boundary.
How quickly ants shift what they identify as an intruder, determines how quickly the whole system can adjust its security. An ant’s odor changes slightly over time. No ant needs to know how to recognize all foreign ants. Instead, since many different ants meet any potential intruder, the chances are high enough that some ant will detect an intruder as a foreigner, and react appropriately.
Such a system makes the colony less vulnerable to hijacking. If every ant were carrying an identical ID card, in the form of a particular odor, then an intruder would merely have to copy that ID. But when both nestmates and intruders vary in ID, it is more difficult to find a fake ID that would be accepted by all nestmates. The mammalian adaptive immune system works in much the same way.
We have much to learn from the ways that ants solve problems without anyone in charge, using simple interactions. They may provide innovative ideas for the systems that we create, and there may even be interesting lessons for human interaction.
Author: Professor Deborah Gordon is a biologist at Stanford University. She is participating in the World Economic Forum’s Annual Meeting in Davos.