Why colonies?

Why do ants live in colonies?

Why is the queen the only egglayer of the colony? And how can the workers consider it a good idea to give up their ability to reproduce, and instead let their mother take care of it? Why do ants live in colonies?

To understand why ants live in organized societies one must first try to understand their evolutionary history. For starters, we consider ourselves knowing this: ants started to organize themselves in simple colonies about 100-200 million years ago. Even though this was a long, long time ago the phenomenon is relatively new on Earth, in comparison to its age. The insects were among the first to settle upon the surface about 400 million years ago, during the geological interval called the Devonian period. The first termites are believed to have arisen around the Jurassic/Cretaceous periods about 200 million years ago. The termite family is not connected to the ants’ family tree and does not share the same gene pool. They belong to their very own order, the Isoptera (while ants belong to Hymenoptera). Just like ants, termites are eusocial and a good example of the possibilities of social behaviors to develop without the influence of each other. A few years later (you know, a couple of million years), more exactly during the Early Tertiary period (50-60 million years ago), ants and termites were the dominant insects on Earth. (1)

So why didn’t this behavior evolve until after 200 million years? The answer is complicated. There are both pros and cons to a eusocial life. After all, there are still solitary insects out there, successfully navigating their way through history and geological periods. The fact is that the large societies and structures that the eusocial group engineer are time and resource-demanding to build and to maintain. When the solitary insect can focus its energy and time on finding food, raising offspring, and surviving long enough to be replaced by the latter, the ants have a more dire task ahead. They must produce large quantities of infertile workers to care for them, in comparison, to the microscopic egg-laying caste (the queens). When the colony is strong enough, which can take years, it can begin its work with fertile offspring. During this, the solitary has gone through many generations of their own. The solitary insects are also very mobile – with the ability to get in and out of areas in a jiffy – whereas the eusocial requires an enormous amount of work and risk-taking to do the same. The advantages of a solitary life must not be forgotten, but nothing really stands a chance against a mature colony of eusocial.

Another advantage of social life is the ability to control terrain and draw up territories. Food and other resources can be claimed and are hard for a solitary individual to get a hold of. And in species where the ants create new queens by letting them mate on the roof and then walk back down, the long lifecycle allows for a firm grip on the surroundings. (2)

The advantages of raising your siblings

But even though we’ve come to know life in a society as something practical and good, why do the ants really need the worker caste? They are infertile and can, at best, lay infertile eggs that develop into males. No new colonies or queens will be the result of their eggs. So why do they sacrifice their ability to produce their own children?

The answer is actually quite interesting, even from a homo sapiens perspective. The ant workers might seem unselfish (altruistic), but their lives of sterility is no altruistic sacrifice. Take yourself as an example, and some simple maths will solve their secret:

You are your mother and father’s offspring – meaning that you are genetically 50% your mother and 50% your father. Your own child, a daughter, carries half of your genes. Ants do not share the same genetical system as us concerning offspring. The males are produced out of an unfertilized egg, meaning the queen does not add seed to it. This way the males are given only one set of chromosomes, meaning he is 100% of his mother's genes. The males do not have a father. This relationship results in the males providing less of a diverse gene pool to the queens he chooses to mate with, compared to the queens themselves. So when the queen lays a fertilized egg (for example a worker) she will mix half of herself (the egg) with half of the male (the seed). But because the male does not have a father, his gene pool is only half as faceted as the queen’s. This way, their daughters will be more related to their mother than their father. They are 75 % of their mother because the male can only contribute with one set of chromosomes, 25%.

And if you remember your own gene relationship with your child, you’ll be able to compare the two. Your child shares 50% of your genes, while the ants share up to 75%. This means, that in order to maximize their genetic offspring, it is more economically efficient for them to raise their siblings rather than raising their own children. This is not possible in a solitary life, without the infertile worker caste. (3)


1. Bert Holldobler & Edward O. Wilson (1995) “Journey to the ants” p. 12

2. Bert Holldobler & Edward O. Wilson (1995) “Journey to the ants” p. 106

3. Bert Holldobler & Edward O. Wilson (1995) “Journey to the ants” p. 99

Further reading