Carpenter bees are large, yellow and black (or blue-black) bees that become active in early spring.  This bee is commonly 2/3 to 1 inch long, usually with a shiny abdomen and a yellow thorax.  Its look-alike cousins (bumble bees) have a fuzzy abdomen.  Although it is rare to be stung by one, their sheer size is scary and people generally stay clear of them.  Bumble bees do not bore into wood, as do carpenter bees.

Carpenter bees get their name from their ability to drill through wood and nest in the hole.  Their drilling creates a near-perfect hole, approximately 1/2 inch in diameter.  The hole is usually located on the underside of the wood surface; including siding, soffits, decks, overhangs, fence posts and window frames.   Although the hole appears to be only an inch or two deep, it rarely ends there.  

The female carpenter bee will turn 90 degrees and bore a channel from 6 inches to as long as 4 feet.  This channel serves as a main corridor from which she will drill small chambers a few inches deep.  These chambers become egg holders.  She will deposit an egg, bring in a mass of pollen for the newly hatched larvae to feed on, and then seal it all off to ensure its development before she repeats the process for the next egg.

The male spends most of his time flying around the nest playing guard. This is ironic as nature has left him ill prepared: he has no stinger.

The female can sting but she is normally very docile. A single pair (male and female) occupies each nest.  It is not uncommon to find several pair of carpenter bees nesting in one structure.  They frequently nest near each other and often in the same area year after year, causing extensive damage.  You may find old holes near newer ones.  Sometimes the female will renovate an old nest gallery and reuse it.