Cicadas are not harmful to humans and they rarely cause significant plant damage. However, the eggs are laid in slits in twigs, so during large emergences of periodical cicadas they can cause substantial damage to branches of trees and shrubs.
Cicadas make a variety of sounds, including very loud buzzing sounds. The males have tymbal organs that include rib like bands on a membrane that can be vibrated very rapidly by a special muscle.
Check out the USDA Forest Service Web page on the Gypsy Moth in North America.  The page contains many links to additional gypsy moth information.
Have you visited the Children's Butterfly Site?
The broods of periodical cicadas (species in the genus Magicicada), and the locations and years of adult emergence, are well documented on the University of Florida’s Singing Insects of North Am
Cicadas are insects in the order Homoptera, and they are related to planthoppers and aphids. They have piercing-sucking mouthparts, which they use to pierce plants and suck out the plant juices.