Carpenter bee damage to deck — Leiden, Zuid-Holland

Carpenter bees bore perfectly round half-inch holes into untreated wood, creating tunnels up to ten inches deep where they lay eggs. Over several seasons, repeated nesting weakens deck boards, fascia, railings, and pergola beams — the structural damage compounds because daughters return to the same tunnels and extend them. Sawdust piles below the holes and yellowish staining from bee excrement are telltale signs. A pest control technician can treat active galleries with residual insecticide dust, seal entrance holes after the brood cycle completes, and recommend surface treatments or wood replacement to prevent reinfestation.