Notes
Slide Show
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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.
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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.
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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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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.
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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
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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
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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
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?? Artificial Examples ??

  • Langton’s Ant


  • Obstacle Avoidance


  • Traveling Salesman Problem (TSP)
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Obstacle Avoidance
  • A moving ant deposits a pheromone trail.


  • The pheromone evaporates with time .


  • Ants tend to follow paths with high concentrations of pheromone.
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Traveling Salesman Problem
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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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