While most people believe carpenter ants eat wood, they actually only nest in the wood:
"The worker ant finds an entry route by gnawing a clean tunnel parallel to the wood grain wherever a crack or crevice exists. The wood is chewed and discarded outside the tunnel."
-- Backyard Bug Brigade (Environment Canada)
This tunnelling is what causes damage to houses and why carpenter ants are considered a pest. But, since I found this nest in some wood at the side of a path I happily snapped many photos; there are more on Flickr, tagged carpenterants.
Incidentally, in looking for info on carpenter ants I happened on this very creepy image of a tissue box infested with the critters. ::shudder::
tags: ants, entomology, photography.