CICADAS: life cycle
11. After succumbing to the romantic ballads, the cicadas mate. Afterwards, adult female cicada lay eggs by piercing plant stems with their ovipositor. The ovipositor is an egg-laying spike located at the tip of the female's abdomen. The spike inserts the eggs into the slit created in the stem. The eggs eventually hatch into small, wingless cicadas known as nymphs. The nymphs eventually fall to the ground and dig below the surface. Here they stay for 17 years [Brood X species], slowly growing into adults. The nymphs live on the sap from plant roots while they grow. They shed their skin at intervals throughout the 17-year process. 12. When the nymphs reach full size, they dig their way to the surface with specially adapted front legs that act as tiny shovels. They surface around nightfall in late spring or early summer. The nymphs then climb to higher ground and shed their skin for the last time. Now fully-winged adult cicadas, they leave their old, empty, nymphal skin behind. Show Time 13. The exact numbers of cicada broods is debated, but a common belief among scientists is that there are at least 13 broods of 17-year cicadas, plus another five broods that emerge every 13 years. Every once in a while, a 13-year brood will emerge at the same time as a 17-year brood, creating tremendous noise pollution.	14. The last to emerge, Brood IX, was seen in the spring of 2003 in parts of West Virginia, Virginia and North Carolina. Do They Bite? 15. Even though they are swarming this summer [2004], you don't have to worry about getting bitten. Cicadas are harmless. They may cause some slowing of the growth of trees from the amount of sap the cicadas consume, but they won't cause permanent damage. Cicadas don't bite or sting in any way. The worst they will do is annoy you with their incessant singing. Limited Run 16. The life span of an adult cicada is short. As mysteriously as they arrive, they will disappear. Most will be eaten by birds and other predators. Even the nymphs are not safe below the ground, as they are often preyed upon by beetle larvae and other ground-dwelling parasites.  17. If you live to be 75 years old, you will only have about four opportunities in your life to hear the song of the Brood X cicadas. If you live in an infested area, you won't be able to miss it. But if you don't, it might be worth your time to go out of your way to hear one of nature's most powerful and elusive performers.
Adapted from: http://science.howstuffworks.com/cicada.htm