A colony of honey bees, Apis mellifera, may contain as many as 60,000 workers. Large colonies of leafcutter ants, Atta, may have several million workers. The largest of all are colonies of the African driver ant, Dorylus, with as many as 22 million workers. One obvious question concerning colony organisation is simply how the workers are coordinated to do the different jobs that need doing, and to respond flexibly to colony needs. Insect societies are not organised from the top down, with the queen issuing instructions for the workers to carry out. In fact, no one individual is in charge. Their societies are 'self organised'. Individual workers react to the local conditions they experience in their colony, and this influences what the other workers do. Overall organisation arises from this.
Task partitioning in Polybia wasps. A wood pulp forager transfers some of its load of wood pulp to a nest builder back at the nest
For example, when a honey bee worker guarding the nest entrance stings an attacker, her sting lodges into the attacker’s flesh and breaks off. The sting releases a volatile chemical known as an alarm pheromone, which alerts more guard bees and guides them to the attacker. Similarly, in many ant species a worker that finds a new food source lays a pheromone trail back to the nest to guide nestmate ants to that source. The recruits lay additional pheromone and many ants are guided to the food source. When the food is used up no more pheromone is laid, and the existing pheromone evaporates. In this way, an ant colony is able to send foragers to where the food is, even though no one ant has perfect knowledge of the whereabouts of all available food sources. Honey bee workers that have found a profitable patch of flowers for collecting nectar or pollen do not lay a chemical trail. Instead, back in the nest, they make 'waggle dances'. These dances tell nestmate workers the direction and distance of the flower patch. By having scout bees to locate new flower patches, and because only foragers working the most profitable patches make waggle dances,
the honey bee colony is able to track the constantly shifting flower resources.
Research on the foraging trail systems in the Pharaoh’s ant, Monomorum pharaonis, and the common garden ant, Lasius niger, has revealed remarkable sophistication in their organisation. Pharaoh’s ants are able to use trail pheromones in three distinct ways that complement each other. They can use a short-lived attractive pheromone to mark the route to food, a long-lived attractive pheromone to act as a memory of previously used routes to food sources, and a repellent 'no entry' pheromone to close off non-rewarding branches at trail bifurcations. Common garden ants use a combination of personal memory, pheromone trails, and ant-to-ant tactile communication foraging. One common lesson from studying the organisation of the foraging systems of ants and honey bees is that they are complex than previously suspected. Social insects probably have some important lessons to teach humans when it comes to being organised, and in doing this effectively.
Selected references
Beekman, M, Sumpter D J, Ratnieks F L W 'Phase transition between ordered and disordered foraging in Pharaoh’s ants' Proceedings of the National Academy of Sciences of the USA 98:9703-9706 (2001).
Evison, S, Ratnieks, F L W 'New role for majors in Atta leafcutter ants' Ecological Entomology 32: 451-454 (2007).
Hart, A G, Ratnieks, F L W 'Task partitioning, division of labour and nest compartmentalisation collectively isolate hazardous waste in the leafcutting ant Atta cephalotes' Behavioral Ecology and Sociobiology 49: 387-397 (2001).
Hart, A G, Ratnieks, F L W '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 (2001).
Hart, A G, Anderson, C, Ratnieks, F L W 'Task partitioning in leafcutting ants' Acta Ethologica 5: 1-11 (2002).
Hart, A G, Ratnieks, F L W 'Task partitioned nectar transfer in stingless bees (Meliponini): work organisation in a phylogenetic context' Ecological Entomology 27: 163-168 (2002).
Hart, A G, Ratnieks, F L W 'Waste management in the leafcutting ant Atta colombica' Behavioral Ecology 13: 224-231 (2002).
Jackson, D E, Holcombe, M, Ratnieks, F L W 'Trail geometry gives polarity to ant foraging networks' Nature 432: 907-909 (2004).
Jackson, D E, Martin, S J, Holcombe, M, Ratnieks, F L W 'Longevity and detection of persistent foraging trails in Pharaoh's ants, Monomorium pharaonis (L.)' Animal Behaviour 71:351-359 (2006).
Jackson, D E, Ratnieks, F L W 'Primer: Communication in ants' Current Biology 16 (15): R570-R574 (2006).
Jeanson, R, Ratnieks, F L W, Deneubourg, J L 'Pheromone trail decay rates on different substrates in the Pharaoh's ant, Monomorium pharaonis (L.)' Physiological Entomology 28: 192-198 (2003).
Helanterä, H, Ratnieks, F L W 'Geometry explains the benefits of division of labour in a leafcutter ant' Proceedings of the Royal Society B 275: 1255-1260 (2008).
Ratnieks, F L W 'Outsmarted by ants' Nature 436: 465 (2005).
Ratnieks, F L W '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 (2008).
Ratnieks, F L W, Anderson, C 'Task partitioning in insect societies' Insectes Sociaux 46: 95-108 (1999).
Ratnieks, F L W, Anderson, C 'Task partitioning in insect societies (II): Use of queueing delay information in recruitment' American Naturalist 58: 536-548 (1999).
Robinson, E J H, Holcombe, M, Ratnieks, F L W 'The organisation of soil dumping by ants' Animal Behaviour 55: 1389-1399 (2008).
Robinson, E J H, Jackson, D E, Holcombe, M, Ratnieks, F L W '“No entry” signal in ant foraging' Nature 438: 442 (2005).
Tofilksi, A, Ratnieks, F L W 'Sand pile formation in Dorymyrmex ants' Journal of Insect Behavior 18: 505-512 (2005).
Tofilski, A, Ratnieks, F L W 'Simple rules based on pile slope are used in the self organization of sand pile formation by Pheidole oxyops ants' Insectes Sociaux 55: 37-42 (2008).