In fact Cicadas emerge on 7, 13 and 17 year periods. The theory for this 'prime number' periodic cycle is quite interesting: https://www.abc.net.au/science/ar

In fact Cicadas emerge on 7, 13 and 17 year periods. The theory for this 'prime number' periodic cycle is quite interesting: https://www.abc.net.au/science/articles/2001/11/27/421251.htm https://www.abc.net.au/science/articles/2001/11/27/421251.ht...