Why don't we look at Cicadas
These are winged insects that evolved around 1.8 million years ago. What is interesting is that their life cycles follow prime numbers. They emerge, mate and die quickly during the spring of either the 13th or 17th year. On these such years, they build an exit tunnel where millions quickly exit and overcome any predators, such as birds, by using their vast numbers to their advantage.
Why every 13 and 17 years?
This way, it will be impossible for any other life cycle to line up with the life cycle of the Cicada.
For example, lets suppose they emerged every 12th year. This would have animals with life cycles of 2, 3, 4, and 6 years to line up perfectly every time they emerged.
The life cycle being a prime number is, what scientists predict, what has been their greatest strength in their survival for over 1 million years.
The cicada example is a brilliant way to introduce prime numbers — nature handing students the 'why' before the definition. Your 12-year contrast example is the key move: when kids see that a 12-year cycle would be perfectly matched by predators with 2, 3, 4, and 6-year cycles, the idea that primes have no divisors stops being abstract. It's exactly the sort of cross-curricular hook that makes math memorable. I run factorcalculator.org, a free site with prime number and factorization tools that teachers use to explore these patterns with students.
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