The cicadas are coming, and there will be millions of them. In some places, concentrations of the dinosaur-era insects will be as high as 1.5 million per acre. The natural phenomenon has been taking place every 17 years since the Ice Age. Some people will be thrilled to see the cacophonous swarm. Others, Purdue University entomologist Cliff Sadof points out, may look at the millions of flapping, bumbling insects with disgust. For both types of people, there's good and bad news: These cicadas will not all be in the same place. Some areas may have massive concentrations — heavily wooded neighborhoods have a good chance of getting swarmed. But some areas won't have any cicadas at all.