Crime and Punishment

Ant societies are remarkably complex and ants exhibit extremely high levels of cooperation. Workers will often sacrifice their own lives to defend the safety of the nest. However, just like human societies, ant nests are also rife with conflict. Where there is cooperation there will always be individuals who try to take advantage and cheat the system.

The defining characteristic of ant colonies (and social insects in general) is reproductive division of labour, where reproduction is dominated by one or a few individuals, known as queens. In this matriarchal system, reproduction is forbidden for most colony members, and in many ant species worker ants are physically incapable of mating. Despite being unable to mate, due to their unusual genetic system, ant workers can still lay male eggs. This gives them the opportunity to try and cheat the system, and in many ant species workers have been found to illicitly try and lay eggs, when the queen isn’t looking. Such crimes do not go unpunished, however, and in many species the honest workers will punish cheaters, either through physical aggression, or by destroying the illegally laid eggs.

The threat of punishment is enough to dissuade most wanna-be criminals, and as long as the queen is around, order is generally maintained in the colony. If the queen is killed or removed, however, worker ants quickly lose their loyalty, and within hours or days of the queen’s disappearance, egg laying becomes widespread.

In some primitive species, workers have retained their physical capability to reproduce, creating greater levels of conflict within the colony. In these species, workers queue in a dominance hierarchy to take over from their queen. Sometimes, those at the top of the queue get impatient, and may try to take over the colony while the current queen is still alive. This is not in the interest of the colony, however, as frequent queen turnover reduces relatedness between workers, which is key to maintaining order in the colony. Thus, when a worker attempts to commit treason, the queen will spray her attacker with a specific pheromone which tells the other workers to attack. The affection of the workers towards the queen is quite fickle, however, and when the queen is too old they will turn on her, supporting regime change!

Despite all this, most ant colonies manage to keep the peace most of the time, at least with only a subtle undercurrent of unrest. However, some ant species make a living out of conflict. Slave-making ants oppress the workers of other species into doing their work for them. There are several different species of slave-making ant, and each uses a slightly different tactic for obtaining their captives. Some species forcefully enter a nest and kidnap the queen, whilst others use chemical trickery to slip into the nest unnoticed. In every case, however, the colony is taken over and the workers forced to help raise the young of their captors. Some slave-making ants are so commited to their way of life that they will die if separated from their slaves, even if food is made available to them. In these species they lack the instinctive behaviours necessary to raise young ants and maintain the nest.

Although ant colonies display remarkably high levels of cooperation and coordination between workers, they are not the utopian paradises they might first appear to be. Whenever the opportunity presents itself, individuals will try to cheat the system and gain benefits for themselves. And, wherever there is cheating, there is punishment. Highly successful ant colonies are those which are able to balance the conflict out.

Articles in this Series:

Part One: Civilisation
Part Two: Agriculture – Crops and Livestock
Part Three: Crime and Punishment

Want to Know More?

• Slavemaking Ants. Taking over the colony… and the slaves don’t even know it!
• Monnin, Ratnieks, Jones and Beard (2002) Pretender Punishment induced by chemical signalling in a queenless ant Nature 419; 61 – 65
• Kikuta and Tsuji (1999) Queen and worker policing in the monogynous and monandrous ant, Diacammasp. Behavioural Ecology and Sociobiology 46; 180 – 189