On Aug 3, 2011, frogymon from Lisle, IL (Zone 5a) wrote:
Grubs spend 2-3 years under ground eating roots of trees/shrubs and surface during summer evenings from mid-June through mid-August when humidity conditions are favorable. They crawl up any vertical surface and break out of their exoskeleton, unfurl their wings and fly off once they are dry. The male's mating call can be heard throughout the day, a shrill whirring sound that is unmistakable. Unless there are extremely high numbers of these cicadas, they do not cause any appreciable damage to the mature plants they favor.