What effect do carpenter ants have on wood when they chew it?

Carpenter ants significantly affect wood by creating irregular but clean galleries as they chew. As they excavate wood, they remove chunks to create nesting sites, leaving behind smooth, polished surfaces which differentiate their work from that of termites, who generally cause more extensive damage with their tunneling. The irregularity of the galleries is due to their nesting habits, as they do not follow the grain of the wood but rather carve out spaces that suit their needs for shelter and reproduction. This behavior is crucial to recognize because it indicates potential structural concerns; although the wood retains some of its integrity, the presence of these galleries can compromise the overall strength of the wooden structure if left unchecked.

The other options are not correct because carpenter ants do not limit their chewing to just softwoods, nor do they impact the wood only in a minor way. Their chewing does not follow the grain exclusively, and they certainly can affect the wood's structural integrity, depending on the extent of their infestation.