Clarification that inactive ants are necessary for the long-term sustainability of colonies

Research Press Release | March 08, 2016

Key Points

・Inactive ants that exist within ant colonies replace other ants that are fatigued and cannot work.

・When other ants are fatigued and cannot work, ants that usually are inactive will perform the work that always must be performed by someone.

・Therefore, in order to guarantee the long-term sustainability of the colony, it is necessary to maintain some number of inactive ants, although at first glance that seems to be wasteful and to lower short-term productivity.


In most social insect colonies there always exist about 20% to 30% of workers that are inactive, and they lower the short-term productivity of the colony. Therefore, a big question is why they exist under natural selection, which acts to increase short-term efficiency.

Research Method

We compared a system in which workers who usually are inactive take over work when all the other workers are fatigued and cannot work, and a system in which all the members work at the same time, to see which system persisted longer in the presence of fatigue. We also investigated whether it is true that, in actual colonies, when ants that do a lot of work are resting, work is done by ants that usually are inactive.


When there was no fatigue, there was no difference in the persistence time between the two systems. However, where there was fatigue, the system that had inactive workers persisted longer. This can be explained by the fact that, when workers who usually work are fatigued and cannot work, the workers that usually are inactive, and are not tired, take over work that someone must perform, or else the entire colony would suffer serious damage. As a result, the colony is able to avoid a dangerous situation. It was also shown that, in actual colonies as well, when working ants are resting, work is done by ants that usually are inactive. In this way we clarified that a non-efficient system of social insects that allows inactive workers to exist is indispensable for long-term sustainability of colonies.

Anticipated Outcomes

Not just for social insects, but also for human organizations, if short-term efficiency of an organization is desired too much, great damage may result. Therefore, with regard to an organization’s operation as a whole, the importance of considering long-term sustainability has been demonstrated.

Eisuke HASEGAWA, Associate Professor

Laboratory of Animal Ecology, Research Group of Ecology and SystematicsDivision of Environmental ResourcesResearch Faculty of Agriculture


Japanese Link

働かないアリはコロニーの長期的存続に必須であることが判明 (02.17.2016)


Lazy workers are necessary for long-term sustainability in insect societies, Scientific Reports (02.16.2016)


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