I don't know how I managed to avoid earlier versions of the Flyz Screensaver, but I just came across version 1.1.2 on VersionTracker and I am pleased to see they've "fixed a bug that was causing the flies and maggots to accumulate at the bottom-left corner of Intel Mac screens" and "increased the maximum number of flies to 40." W00t!
If you like being grossed out, or like grossing out others, the Flyz Screensaver might be an appropriate download for you. Flyz is "an infestation of ewwey, gooey, flies and maggots, making a mess of your Mac's screen." And if that's not appealing enough, perhaps the price tag (free, although there's an enhanced version for $5) will lure you in.
Of course some people already have a similar effect without having to download anything at all!
Oh, how I long for the days when Flying Toasters was enough to keep us entertained when our screens were idle...