Want to really creep someone out. Try my free Spiders Screensaver. I am not responsible for wet pants, thrown computers, etc...
Spiders:
http://tinyurl.com/9ljdobc
If the Spooky Spiders creeped you out then this one will annoy the heck out of you.
In Screen Saver Settings, if you turn off Exit on Mouse Events, the flies will react to your mouse movement. Just remember you need press a key such as Esc to exit out of the screen saver.
Flies:
http://tinyurl.com/95lsaqa
Note: All installers are Digitally Signed with my name, Steve Blosser to ensure the integrity and saftey of the files.