How did the cicadas decide that they would wait a prime number of year before emerging?

So how do the cicadas know how to calculate prime numbers? ... They're cicadas. The pattern probably emerged as a result of Darwinian natural selection: cicadas that naturally matured in easily divisible years were gobbled up by predators, and simply didn't live long enough to produce as many offspring.

1. Why do cicadas come out in prime number years?
2. Why do cicadas wait 17 years to emerge?
3. How do periodical cicadas know when to emerge?
4. Why do cicadas emerge in large numbers?

Why do cicadas come out in prime number years?

The overwhelming number of cicadas emerging at once is protective. It's a strategy called predator satiation. ... Both 13 and 17 are prime numbers, meaning they're divisible only by 1 and themselves. This means that emergences rarely overlap with predator population cycles that occur in shorter intervals.

Why do cicadas wait 17 years to emerge?

As trees go through their seasonal cycles, shedding and growing leaves, the composition of their sap changes. And when cicada nymphs feed on that sap, they likely pick up clues about the passage of time. The 17th iteration of the trees' seasonal cycle gives the nymphs their final cue: it's time to emerge.

How do periodical cicadas know when to emerge?

The cicada nymphs hatch from their eggs in trees. ... No one knows for sure, but scientists speculate that periodical cicadas have an internal molecular clock that allows them to sense the passage of time through changes in the tree sap that they eat.

Why do cicadas emerge in large numbers?

An abundance of prey allows predators to reproduce in greater numbers, so for example birds with a life cycle that is a factor of the cicadas' would be in abundance the next time they emerged. This could establish a rhythm resulting in lots of predators regularly being around in years when there were lots of prey.