You will see round holes and a coarse sawdust-like substance called frass underneath the holes. You may find old holes near the newer ones. Old nests can be used year after year by the carpenter bee. During the spring, the males seek out the females, hovering around females that found some unfinished wood, such as under eaves, railings, etc. The males are territorial and will confront you if you enter their territory, but they are incapable of stinging.
Females have a stinger, but are very docile.
Females will nest in a all types of wood, but prefer weathered and unpainted wood. Male carpenter bees tend to be territorial and can buzz around you if you approach closely, sometimes hovering a short distance in front of your face or buzzing around your head. Since males have no stinger, these actions are just for show and intimidation. The female bee can squeeze through incredibly tiny places to bore into untreated wood. In the early spring, before the carpenter bees can begin to bore into the wood an once of prevention is worth a pound of cure.