Social insects show extraordinarily high levels of cooperation, giving up their reproductive opportunities and even sacrificing their own lives to save the colony. The social insect colony is a well-oiled machine, each part has its own key role to play, together forming an intelligent and adaptive society. Most people are familiar with the highly advanced social insects, such as honeybees and leaf cutter ants. Their societies are huge and intricate, and we have gained many fascinating insights from them. However, they tell us very little about how these societies evolved, or what it meant to be cooperative in a more primitive sense.

The most striking characteristic of advanced social insects such as these is that almost everyone in the colony is physically incapable of mating and reproducing. One or a few individuals (queens) retain this ability whilst the others are committed to sacrifice themselves for the good of the queen. This seemingly counter-intuitive self-sacrifice is favoured by evolution because the altruistic workers are closely related to the reproductive queen. When they help her to produce offspring, she passes on genes which they share with her. But again, sterility in the worker caste is a feature of highly advanced social insect societies, and tells us little about the early evolution of social behaviour.

Some social insects alive today still have a simpler society, similar to what might have occurred when sociality first evolved. In these societies, although workers generally refrain from reproduction, they are still capable of it. This gives them many more options compared to their sterile cousins, and the line between queen and worker in these societies is often blurred. Subordinates in these simple societies can choose to work, they can choose to leave found their own nest, or they can even try to sneakily lay eggs when their queen isn’t looking. What they choose to do often depends on a delicate balance of costs and benefits, and this varies from species to species.

In the tropics, where colonies are not limited by the necessity to hibernate over winter, and thus nests can be potentially immortal, it is common for the queen to die before the colony does. In circumstances such as these, when the royal position opens up, the workers have an opportunity to take over and reproduce. This opportunity is much better than leaving to found your own nest, as it comes complete with an inheritance – subordinate workers. In some species, the subordinates left on the nest after their mother dies will fight it out to decide who is next in line, while in others a prearranged hierarchy decides the heir to the throne. These hierarchies are generally quite dynamic and can change rapidly, with high-ranked workers being displaced and losing their bid for the throne. For an individual sitting in a high-rank position, the key is to try and ensure that you take over the throne before you lose your rank or die.

A Royal Strategy

What can an individual ant do to increase it’s chances of inheriting the throne? There are a number of options:

1. Be Lazy
   Working hard tends to make you die younger. So, if you want to be sure you out live your royal parent and inherit the reproductive role, your best bet is to stay put and do as little as possible. In the socially simple Dinosaur ant (Dinoponera quadriceps), high-ranking workers spend more time sitting around the nest doing nothing than other colony members. And in simple wasps societies, such as those of the paper wasp Polistes dominulus and the hover wasp Liostenogaster flavolineata, individuals closer to inheriting the throne tend to work less hard.
2. Don’t Take Risks
   One of the most dangerous jobs a worker can perform is foraging. This requires them to leave the safety of the nest and venture out into a world filled with predators and the very real possibility of getting lost. High-ranking dinosaur ants refuse to leave the nest for foraging or taking out the rubbish, and recent research has shown that they also refuse to defend the nest against attack, letting the lower-ranking subordinates take that serious risk. Likewise, it is the low-ranking colony members in the social Damaraland mole rat (Cryptomys damarensis) who defend the nest against attack.
3. Monitor the Situation Closely
   Figuring out when the time has come to overthrow the current queen is also crucial to success. Social insects don’t always wait for her to die gracefully; in Dinosaur ants, subordinates will pin her down and force overthrow when her fertility drops too far. And high-ranking workers spend an awful lot of their time inspecting and generally hanging around her eggs – this may be a way of assessing her fertility, enabling workers to pick their moment for a coup.

These three tactics may enable a high-ranking worker to hold onto her position just long enough, and sense when the time is right to take over. And should she succeed, she inherits a well established nest, a substantial workforce and the opportunity to mate and produce her own young. Should she fail, then she’s either dead or forced into a low-rank position for the rest of her life. And as a low-ranker, her best bet is to work as hard as she possibly can and take any necessary risks in order to protect the colony, as it contains her relatives and the only opportunity for her to pass genes to the next generation. So, it may be that these colonies reach a form of homeostatis, high-rankers prefer to be lazy, and low-rankers prefer to work hard, and everybody is happy, or as happy as they possibly can be.

Simple eusocial societies, such as those of Dinosaur Ants, Paper wasps and mole rats, can reveal subtly in social behaviour that are not so evident in more advanced societies, and suggest mechanisms by which social order was maintained during the early stages of eusocial evolution.

Want to know more?

• Asher et al (2013) Division of labour and risk taking in the Dinosaur ant, Dinoponera quadriceps (Hymenoptera: Formicidae). Myrmecol.News 18: 121 – 129
• Field (2009) Social stability and helping in small animal societies. Phil.Trans.Roy.Soc. B 364: 3181
• Cant & Field (2001) Helping effort and future fitness in cooperative animal societies. Proc B 268: 1959 – 1964
• Monnin & Peeters (1999) Dominance hierarchy and reproductive conflicts among subordinates in a monogynous queenless ant. Behav. Ecol 10: 323 – 332

Featured image copyright Claire Asher 2011