Cicadas are amazing animals, particularly the Magicicadas. Different types live underground for either 13 or 17 years before emerging in huge numbers to breed and then return underground. One group of cicadas (known as Brood XIX) is currently appearing across Tennessee and other states.
The really interesting thing here is that their lifecycles are prime numbers. It turns out that only appearing every 13 or 17 years minimizes the amount of competition that the cicadas face when they emerge.
This is interesting from a evolutionary game theory perspective because it is possible to consider how the ‘strategy’ of only appearing in prime number years can be a successful one.
Imagine we started with three groups of cicadas, one group that appears every 12 years, one group that appears every 16 years and one group that appears every 17 years. Every 48 years the 12 year group and the 16 year group will appear at the same time. When this happens they will cross-breed and end up with a mix of lengths of time between appearances. This will spread the population out over different times so they will emerge in smaller groups and a bigger percentage of those groups will be eaten. There is safety in numbers so it is better to emerge as a big group.
The 17 year group will only appear with one of the other groups every 204 (17 x 12) years or 272 (17 x 16) years. This will mean that they do not cross-breed with other groups very often and nearly always emerge as one big group. This means that they do better over a long period of time than the 12 and 16 year populations that meet much more often.
The moral of the story is that sometimes it is better to look for a strategy that avoids competition rather than trying to beat the competition.
If you want to see what millions of cicadas all appearing at once looks and sounds like then check out the video:
The modelling of the different populations has been done and you can read more about it here.