Why do carpenter bees drill holes in wood?

The single most useful fact about carpenter bees is that they are not eating your wood. A female bee bores her nearly perfect, roughly half-inch entry hole, turns to follow the grain, and excavates a series of small chambers, each stocked with a ball of pollen and a single egg. That's the entire purpose of the tunnel: a nursery for the next generation, built once per bee per season. The bees themselves feed on flower nectar and pollen, exactly like any other bee, and get nothing nutritionally from the wood they've removed.

That distinction matters because it changes what kind of problem this is. A pest that eats wood for food — a termite, for instance — keeps consuming as long as it's present, and the damage compounds continuously. A carpenter bee finishes her tunnel, provisions it, and her work in that hole is essentially done for the season.

Per University of Maryland Extension, 'the nest of a single bee will not cause structural damage.' A new tunnel runs about four to six inches — cosmetically noticeable, structurally irrelevant. If that were the whole story, this would be a purely cosmetic page.

It isn't the whole story, because carpenter bees have a habit that matters: they frequently reuse and extend an existing tunnel rather than boring an entirely new one each season, provided the wood stays unpainted and unsealed. University of Maryland and University of Georgia Extension both document reused galleries reaching extreme lengths — up to roughly ten feet — in wood that's gone untreated for years. That's the honest compounding pathway: not the hole itself, but the same hole, reopened and lengthened, season after season, on a board nobody ever painted.

There's a secondary mechanism worth naming honestly, because it changes the worst-case picture: woodpeckers hunt carpenter-bee larvae inside occupied tunnels, and they excavate the wood around the gallery to get at them. A tunnel that a bee alone would have left at four to six inches can end up substantially enlarged by woodpecker activity going after the grubs inside it — often turning a cosmetic hole into a visibly damaged patch of siding or fascia.

This is why the two genuinely compounding pathways in this whole picture are (1) multi-year reuse of the same unsealed tunnel and (2) woodpecker follow-on into an active gallery — not the simple fact that a bee drilled a hole this spring. A single finished, abandoned tunnel that gets promptly filled and painted essentially stops there; it's the untreated, repeatedly reused board that develops a real problem.