About a week and a half ago, we started noticing a strange whirring sound outdoors. At first, I ignored it, thinking that it must be machinery doing work somewhere out on the road. But it was constant and sometimes, loud enough that we could hear it inside the house. When the newspaper ran an article about it, we realized we were hearing an unusual natural phenomenon - 13-year cicadas. These harmless but noisy bugs have the longest developmental period of all N. American insects, growing underground as nymphs for 13-17 years, depending on which brood they belong to. We're being treated to the song of Brood XIX, which last emerged in 1998, and won't be heard again until MB is 21 years old. Read more here.
This video is a good example of the sound. It isn't quite this loud in our yard, thankfully.