Glowing Pathfinder Bugs, a playful piece by Squidsoup commissioned by Folly, has been shown at several Portable Pixel Playground events in 2008 and 2009.

The bugs analyse the shape (topography) of the sand around them, preferring to move gently downhill. This means they can be shepherded, enclosed within walls of sand, encouraged to meet each other (at which point strange metamorphoses happen; they merge into larger caterpillars then, if you're lucky, into butterflies). If they get frightened, the pop and disappear. And with kids, this is what happens most often...

More info:
squidsoup.org/bugs
folly.co.uk/node/1358