Cincinnati Zoo bug expert Randy Morgan says Monday's scattered showers may have only been "wet" enough to cause a small percentage of the Brood X cicadas to leave their homes in the soil. Once out of the ground, the billions of cicadas will head next to trees or elevated locations to molt. Morgan says you can't exactly set your clocks by the cicada invasion. Different soil temperatures and conditions will cause the little, annoying creatures to emerge. Their estimated time of arrival is still sometime between May 9 and May 19th..