What damage do carpenter ants cause?

Ask most homeowners what carpenter ants damage, and the mental picture is an army of ants eating through a house's frame the way termites are imagined to. That's not how carpenter ants work, and it's not the honest ranking of what actually gets damaged. UNH Cooperative Extension does place carpenter ants alongside termites among New Hampshire's most troublesome structural pests — that classification is earned — but the mechanism and the real driver behind it are different enough to change how the risk should be ranked.

Carpenter ants excavate wood to create nest space; they cannot digest cellulose and gain no nutrition from the wood itself, unlike termites. More importantly, they overwhelmingly select wood that's already damp or decaying from an existing moisture problem — a roof leak, failed window flashing, a slow plumbing drip, or poor grading. That's why this ledger ranks the moisture and decay defect first: it's the actual root cause, and the carpenter ants are a symptom pointing at it, not the origin of the problem.

The ant galleries themselves rank second, and genuinely so — University of Maryland Extension notes that tunneling 'may cause serious structural damage if it occurs in key timbers,' though 'nest sites rarely exceed a few square feet.' That's a real, bounded threat, not a house-eating one, and it develops over years rather than weeks.

Below the structural rows, satellite nests in insulation or wall voids are more nuisance than threat — they may displace some insulation but rarely represent meaningful structural loss on their own. Frass, the coarse, pencil-shaving-like debris carpenter ants push out of their galleries, ranks lowest of all: it's appearance only, and its real value is as a diagnostic clue that tells you where a colony is working, not as damage in itself. Treating frass discovery with the same urgency as a compromised sill misreads what the evidence actually supports.