Carpenter bees will tunnel into wood in order to build a nest. Typical sites include wood siding, eaves, window trim, decks, and wooden outdoor furniture. These wood-destroying bees generate sawdust piles and frass, a mixture of excrement and body parts, around the entry holes.
When carpenter bees tunnel, they make a perfectly round hole around the size of a nickel and go in roughly an inch, making a sharp turn. Inside this tunnel they lay their eggs and place a ball of pollen for the eggs to feed on. They continue to bring new pollen back to the nest through the spring and summer.