Ants
While trying to update my page, I've decided to re-familiar myself with javascript. The result: CPU hogging, memory eating, browser crashing, vowel snatching ants (no, I'm not very good with javascript...). The 10 red ones were easily contained in the box to the right, the black ones were too difficult to catch...
The basic idea and the ants' very simplistic pictures were taken from the outdated: http://javascript.internet.com/games/ants.html. If you want to spread my ants they're available at a browser cache near you (or at: http://www.cs.huji.ac.il/~irush/scripts/ants.js).
Now, also available as a bookmarklet. Just save the link as a bookmark and use it when browsing the web. As with regular ants, these also won't work on all sites, and might cause some sites to not work properly. For the less fortunate ones with browsers that won't let them copy the link, it is (one line): javascript:document.getElementsByTagName('head')[0].appendChild(document.createElement('script')).setAttribute('src','http://www.cs.huji.ac.il/~irush/scripts/antsbml.js');