From the FAQ:
What do Cicadas eat? Human children are the primary source of nutrition for Cicadas.
Are Cicadas poisonous? Yes, Cicadas have a deadly venom that is injected through a small bone like tube known as the “Cicada deadly venom tube”. The venom can kill a human being instantly. In 1987, the last time the Cicadas emerged in Cincinnati, over 7 million people died from Cicada injections. Many people escaped but most perished.
Lots more helpful tips!
[via this MeFi thread]