In fluid mechanics, the cheerio effect is the tendency for small wettable floating objects to attract one another. An example of the cheerio effect is the phenomenon whereby breakfast cereal tends to clump together or cling to the sides of a bowl of milk. It is named for the breakfast cereal Cheerios and is due to surface tension and buoyancy. The same effect governs the behaviour of bubbles on the surface of fizzy drinks.
--Wikipedia on the cheerio effect