That video is very interesting. I have heard they swarm every 7 years. Do not know is this is true or not.
It appears, depending on the species, the larva burrows underground for 2, 13, or 17 years, then emerges to mate again. Here is a link with some info:
http://www.cicadas-pictures.com/cicadas_life_cycle.htm
In Oak Creek Canyon, the ‘chorus’ seems to run up and down the canyon, in a strange, rolling sound. It gets louder and louder, then gradually fades into a quiet ‘screeching’, then repeats.