C1139 Social Insects. Principles of self-organization. Lecture 13
Principles of Self-Organization
Aims
1. To explain the general principles behind self-organization.
2. To give specific examples in the balancing of foragers and receivers in honey bee colonies and in the
pheromone trails of ants.
Objectives
1. Learn and understand the basic principles
2. Learn the examples in relation to the principles
Introduction to Part 3 of course
The second part of the course focused on conflicts over colony reproduction among individuals or groups of
individuals within an insect society and how these conflicts may be resolved. For example, conflict over sexallocation ratio or whether to rear the queen’s sons or workers’ sons. However, in many areas of colony life there
is no conflict. Consider foraging. If one worker brings food back to the nest this will help the colony survive and
reproduce better. If a worker helps a nestmate worker to collect more food this will also help the colony survive
and reproduce better. The food all ends up in the same place whoever collects it. Thus, there is a strong incentive
for workers to cooperate to enhance colony foraging efficiency. Thus, in an insect colony we have both altruism
and cooperation. The third part of the course focuses on the organization of the workforce in areas of colony life
in which there is no conflict. There may be conflict over reproduction, but this need not carry over into foraging.
Big Picture
Insect societies are well organized. But how do they achieve this? About 100 years ago, the Belgian writer
Maurice Maeterlinck all but invoked the existence of supernatural forces to explain the coordination of honey
bee colonies. One of his quotes specifically raises the issue of who is in charge “What is it that governs here?
What is it that issues orders, foresees the future, elaborates plans, and preserves equilibrium?” Over two
thousand years previously an important contribution to this problem had already been made “Go to the ant, thou
sluggard: consider her ways, and be wise. Which having no guide, overseer of ruler, provideth her meat in the
summer, and gathereth her food in the harvest.” (The Bible, Proverbs 6: 6-8). In insect colonies, no one is in
charge. The queen may be the chief egg-laying individual but in most social insect colonies she does not issue
instructions. In fact, most activities are self-organized. This means that the overall or global pattern of
organization arises from the interactions of many individuals, each responding to its local conditions.
Maeterlinck, M. 1900. La vie des abeilles [The life of the bee]
Self-organization: basic concepts
Many systems are composed of “sub-units” or “agents”. Examples include the workers in an ant colony, the cells
in a multicellular organism, or even the grains of sand on a beach or dune. Individual agents react to local
conditions and the global pattern arises from agent behaviour. No one agent is in overall charge. No one agent
“knows” the overall state of the system.
Self-organization is not the only mechanism by which a group can become organized. Imagine that a
group of individuals are constructing a nest or structure, or are trying to organize themselves in some particular
way. There are several possible alternative mechanisms that do not use self-organization: following a leader who
gives instructions; using a plan or blueprint that shows what needs to be done; using a recipe that results in the
correct outcome; using a template or mould as a full-size guide. In addition, a combination of mechanisms
including self-organization may be used.
Self-organization has several advantages. It is simple to implement as the global pattern can arise from
relatively simple rules by which the agents interact with each other and their environment. It can be robust. For
example, a self-organized system will not crash if a few agents are gained or lost. But perhaps most importantly,
it is practical.
Central control may not be easy to achieve in an insect society. How would a worker or group of
workers who were in charge gather information from other workers on what was going on in the colony, process
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C1139 Social Insects. Principles of self-organization. Lecture 13
the information, and communicate back to the other workers telling them what to do? Even in human society,
central control is not easy to achieve. The centrally-planned economies of 20th century communist countries
performed badly in comparison to the self-organized economies of western democracies. Most human systems
involve a combination of leadership (central control) and self-organization. For example, market forces are
involved in ensuring that food is grown, transported, and available to buy in shops. But central control may aim
to adjust the outcome in some way. For example, by allowing or not allowing a large supermarket to be built in a
certain area, by regulating food quality, or even by regulating the prices of certain essential food items. (In
Mexico, the prices of staple foods such as corn tortillas are fixed.)
Camazine, S., Deneubourg, J.-L., Franks, N. R., Sneyd, J., Theraulaz, G., Bonabeau, E. 2001. Self-organization in
biological systems. Princeton University Press.
Pheromone trails to food
Many ants (and also some termites and stingless bees) have pheromone trails leading from the nest into the
environment. The global goal is that trails lead to food and that workers are directed to rewarding food locations.
How could this come about via self organization? A few simple rules, in which individual foragers react to local
conditions, can achieve this. If a forager walking around outside the nest finds food, she lays trail pheromone
back to the nest. If a forager walking around outside the nest finds a trail, she follows it to the food. In this way
the global adaptive pattern arises from agent behaviour. Trails leading to food sources are established.
There is both positive and negative feedback in this trail system, meaning that more or less ants can be
directed to particular locations. Positive feedback is the attraction of more ants to rewarding locations and can
come about because successful foragers lay pheromone to these locations and trails with pheromone attract more
foragers. Negative feedback is the non-attraction of ants to locations with no food of where the food is used up
and can come about if unsuccessful foragers do not lay pheromone and existing pheromone evaporates.
Computer simulations using these rules can result in an ant colony “intelligently” discovering food,
sending more foragers to this location, and ceasing to forage when the food is used up. Whether this is
intelligence is a matter of definition. But what is certain is that, collectively through sharing information, the
forager workers have solved a problem. What intelligence there is lies at the group level because the individual
workers are largely ignorant of the global situation.
In an insect colony the global pattern will be adaptive because natural selection will favour genes that
result in colonies that collect food more efficiently, as these colonies will survive and reproduce better. Natural
selection does not select genes that directly result in global properties of a trail system. No such genes exist.
There is no gene for a specific pattern of trails. Instead, natural selection can select genes that affect the local
rules and responses of workers, which in turn influence the global properties of the trail system.
Different species of Eciton army ants have different raid patterns. A broad raid pattern is suited for
capturing poorly-defended prey in a wide area. In contrast, a pattern that concentrates ants in small areas is ideal
for attacking well-defended prey such as the nests of ants and termites. Different raid patterns that look very
similar to those of Eciton army ants can be generated in a computer simulation by adjusting the local rules used
by forager workers, such as how readily they lay trail pheromone and how they respond to differences in trail
pheromone amount at a trail bifurcation when choosing to go left or right.
Self-organization is not confined to biological systems. Many physical systems involve selforganization. The sand grains in a sand dune form distinctive patterns according to the way that they interact
with each other and their environment. However, natural selection has not been altering the behaviour of sand
grains to create more adaptive sand patterns.
Deneubourg, J.-L., Goss, N., Franks, N., Pasteels, J. M. 1989. The blind leading the blind: modelling chemically mediated
army ant raid patterns. Journal of Insect Behaviour. 3:719-725.
Jackson, D. E., Ratnieks, F. L. W. 2006. Primer: Communication in ants. Current Biology 16 (15): R570-R574
Ratnieks, F. L. W. 2008. Biomimicry: further insights from ant colonies? Pages 58-66 in: Liò, P., Yoneki, E., Crowcroft, J.,
Verma, D.C. (editors) Bio-Inspired Computing and Communication. Springer Verlag, Berlin & Heidelberg.
Balancing nectar foragers and receivers in honey bee colonies
In honey bee colonies, nectar foragers do not unload their nectar directly into cells. Instead, they transfer it to
receiver (= storer) bees who then place it in cells. This is an example of task partitioning. That is, the task of
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C1139 Social Insects. Principles of self-organization. Lecture 13
collecting and storing each load of nectar is divided into collecting and storing sub-tasks carried out by different
workers.
For the system to function efficiently there must be a balance in the numbers of foragers and receivers. If
not, time will be wasted in queuing to be served. Balance is achieved through self-organization, based on the
reactions of individual foragers to the length of time they have waited to be unloaded.
If a forager waits a long time it is more likely to make the tremble dance. This recruits in-nest bees to act
as receivers. If the delay is short a forager is more likely to make the waggle dance. This recruits additional
workers to foraging, and also tells them where the flowers are.
Foragers often transfer their nectar to several receivers. They probably do this to gain a better estimate of
the average delay in being served. Each forager can only base its decision about whether to make a waggle
dance, tremble dance, or no dance on its own “local” experience and it can also be lucky or unlucky in how
rapidly it is served. The value in unloading to several receivers is for an individual to gain more information
concerning the state of the system so that she is more likely to exert the correct feedback to the system.
Anderson, C, Ratnieks, F. L. W. 1999. Worker allocation in insect societies: coordination of nectar foragers and nectar
receivers in the honey bee. Behavioral Ecology and Sociobiology 46: 73-81.
Anderson, C., Ratnieks, F. L. W. 1999. Task partitioning in insect societies. 1. Effect of colony size on queueing delay and
colony ergonomic efficiency. American Naturalist 154: 521-535.
Hart, A. G., Ratnieks, F. L. W. 2001. Why do honeybee (Apis mellifera) foragers transfer nectar to several receivers?
Information improvement through multiple sampling in a biological system. Behavioral Ecology and Sociobiology
49: 244-250.
Ratnieks, F. L. W. 2001. Are you being served? Supermarkets and bee hives. The Beekeepers Quarterly 67: 26-27.*
Ratnieks, F. L. W., Anderson, C. 1999. Task partitioning in insect societies. Insectes Sociaux 46: 95-108.
Ratnieks, F. L. W., Anderson, C. 1999. Task partitioning in insect societies (II): Use of queueing delay information in
recruitment. American Naturalist 58: 536-548.
Seeley, T. D. 1995. The wisdom of the hive. Harvard University Press. Chapter 6 “Coordination of nectar collecting and
nectar processing”.
* this article, which you have been given, summarizes the topic in an easy to understand way
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