The Sound of Science - 'Cicada Songs'

It’s that time of year again: when cicada songs flood our warm summer nights, announcing their presence as they attract mates. As a kid I was told they only came out every 7 years. I was confused because I heard them every year. It turns out whomever told me they emerge every 7 years was wrong on two counts: some species of cicadas emerge every year, and some emerge every 13 or 17 years.