In regards to Jane's comment on solitary Carpenter bees....
At least a few species of the genus Xylocapa have the habit of nesting
together.  Essig, in "Insects of Western North America" (now out of print)
says that Xylocapa varipuncta makes burrows that are 5-12 inches long
that may or may not be straight but which follow the grain of the wood.
Several burrows may have a common entrance.  In large numbers, carpenter
bees can be damaging to building timbers and telephone poles.
A very interesting critter, none the less.
 
Dave Pehling
WSU Coop. Extension
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