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2	Ant / Insect Facts When combined, all ants in the world weigh about as much as all human beings. In the Amazon rainforest, ants and termites make up nearly 1/3 of the total animal biomass. About 9,500 species of ants are known. Scientists believe at least twice as many species of ants have yet to be discovered. There are one million trillion (10¹⁸) insects alive at any moment. One percent of these are ants. There are ten thousand trillion (10¹⁶) live ants at any moment. Hölldobler, Wilson, Journey to the Ants, Harvard University Press, 1994.
3	Social Insects Each insect in a social insect colony seems to have its own agenda. Collectively the colony appears very organized. There is no “colony supervisor.” Examples of insects that live in colonies: Ants Termites Bees, most are solitary Wasps, most are solitary Bonabeau, Dorigo, Theraulaz, Swarm Intelligence: From Natural to Artificial Systems, Oxford University Press, 1999.
4	Impressive Collective Behavior Forming Chains (weaver ants) Hunting raids Nest construction Performing tasks Worker ants can specialize Certain species have two or more physically different types of workers Task switching
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6	Swarm Intelligence Swarm Intelligence: any attempt to design distributed problem-solving devices inspired by the collective behavior of social insect colonies or other animal societies.
7	A Colony as a Problem-Solver Decentralized problem-solving system, composed of many relatively simple interacting entities (insects) Problems solved: finding food, building nests, efficiently dividing labor, efficiently feeding brood, etc. Features Flexible: adaptation to changing environments Robust: colony functions even though some individuals do not Insects have limited cognitive abilities
8	Collective Activities & Self-Organization Many aspects of the collective activities result from self-organization “Something is self-organizing if, left to itself, it tends to become more organized.” –CS, Notebooks “Self-Organization in social insects is a set of dynamical mechanisms whereby structures appear at the global level of a system from interactions among its lower-level components” –SI
9	Ingredients of Self-Organization in Social Insect Colonies Positive Feedback Negative Feedback Amplification of Fluctuations Multiple Interactions (in two forms) Direct Interactions Indirect Interactions, stigmergy
10	?? Artificial Examples ?? Langton’s Ant Obstacle Avoidance Traveling Salesman Problem (TSP)
11	Obstacle Avoidance A moving ant deposits a pheromone trail. The pheromone evaporates with time . Ants tend to follow paths with high concentrations of pheromone.
12	Traveling Salesman Problem
13	Ant System and TSP Initially place the ants randomly at cities Begin a tour Visit each city according to a probability Update the pheromone along the paths taken Repeat tour
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