In "Swarm," Bruce Stirling takes the reader inside the Nest, a vast honeycomb of caverns within an asteroid orbiting Betelgeuse, peopled by hundreds of thousands of large, insectlike aliens, including eight-legged, furred workers the size of Great Danes, and horse-sized warriors with heavy, fanged heads. In "The Screwfly Solution," Raccoona Sheldon creates a world much like modern America, except that something--an insect virus, a mass religious delusion,...