The cicadas have been underground for thirteen years, feeding on the sap of roots. Now, the concentrated power of all those years of photosynthesis is unleashed in their songs. Their massed buzzing turns into a roar that penetrates buildings and overpowers conversation.
Around Sewanee, these insects are much more common in the valleys and low mountain slopes than they are in the uplands. Presumably, the cicadas thrive where the soil is deep, rich and full of well-provisioned plant roots.