They make slits in twigs or branches to insert their eggs. Nymphs that hatch from the eggs drop to the ground, burrow into the soil and find tree roots to feed on until they emerge 13 years later. They don't bite or sting, and are not known to be toxic or to transmit disease. But they are a threat to small trees with trunk diameters of 2 inches or less, Nixon said. Their egg-laying may cause branches to snap off in windy conditions.
Insecticides are only marginally effective.
Young trees with small trunks can be protected with hardware cloth, screening or tree wrap during the few weeks that the adult periodical cicadas are present. If you live in an area where the periodical cicadas are expected, it doesn't necessarily mean you will see them. If an area has been cleared of trees and shrubs within the last 100 years, or if it was originally a prairie, periodical cicadas are unlikely to be present, Nixon said. These insects don't fly very far from where they emerge. That, combined with their long generation time, means they spread very slowly.