From The Idle Screen:
Screen saver featuring everybody's favorite, the cockroach. Try the full version free of charge, payment is by the honor system. Up to 25 realistic roaches in slightly different random sizes and speeds run across your desktop. You can choose to have an extra-large roach generated every once in a while, and speed and size can be adjusted to suit your system and preference. Roaches randomly change directions like real ones do. Version 2.0 adds transparency and roaches can now scamper across the users current desktop.