Plagues and other great diseases are important parts of history and some settings. They defy man and may even defy God in their swift and terrible punishment upon the body of society.
The PCs discover a large white ball in the branches of a tree, or in a niche in a cave. Unless magically examined, or by a PC with a specialty in insects, it is a plain, smooth white ball. After a short time, it hatches and releases hundreds of spiders, cockroaches, some other nasty bug