Caulobacter crescentus can be found as a sparse constituent of freshwater streams and lakes -- and tap water. The bacterium isn't dangerous, but marvelous. Somehow the species manages to eke out a living without access to much food. It also is capable of creating two kinds of cells -- "stalk" cells (the two cells in the lower part of the picture) and "swarmer" cells (the two cells above). Stalk cells possess a long, rigid organelle that attaches to rocks using an incredibly strong natural glue. Once anchored, the cells may produce mobile swarmers, which use their flagella to colonize faraway pebbles.