"In the same years in which the little girl had begun collecting butterflies, the district they were in had suffered from a serious plague of may-beetles. The children were furious with the beetles and crushed them unmercifully. At that time my patient had seen a man who tore the wings off may-beetles and then ate their bodies." --Sigmund Freud, "The Interpretation of Dreams"

• The beetle-eating man seems a bit mad, though harmless enough after a little talking to. The PCs may be on the verge of losing interest until he begins ranting about the "Bug Thing" in woods. He says he's eating the beetles so it'll think he's one of them when it gets to town and starts looking for food...
• When the PCs approach the man, he seems hardly capable of answering a single question. When he finally opens his mouth, keen-eyed PCs may notice that he's not eating the beetles at all; they're still crawling around in there. As soon as the PCs look ready to apprehend him, his entire body dissolves into a swarm of bugs and he escapes down the nearest sewer grate...
• After the may-beetle plague commences, some people just seem... different. Less kind, less emotional, less human. No one really knows what to do until they stumble upon one of the townsfolk in a strange chrysalis with one of the beetles. Knowledgeable PCs may be able to figure out that the beetle has its victim paralyzed and it switching bodies with it. It may dawn on the PCs now that it's only those who seemed different that took pleasure crushing the beetles...