decibels, the same intensity as a jack hammer. >> how do they know after 17 years when to emerge. >> there is a series of bio- chemical cascades, hormones that rise and fall that set off a trigger. and if you have a certain hormone level and the temperature of the soil is 64 degrees it's go time, they have three or four weeks to get the job done. they need to find a mate, do the actual mating, females need to lay the egg, and then death occurs. >> reporter: if you are a cicada that is a really, really exciting time. >> if you spend your entire juvenile stage, 17 years >> repr:cadaberingou have three. says n to worry, they don't bite or sting. >> they actually pose no harm to humans.goy fi n make the next generation of cicadas. >> and because of our warmingara emerging anywhere from a week to