Carpenter bee calls and samples continue to arrive, and the reported distribution has spread northward since the last update on this "southern" insect. See the map below.
Carpenter bees look like bumble bees but behave much differently. While bumble bees are social (large colonies living together) and live in the ground or in existing cavities, carpenter bees are solitary and nest by drilling holes into exposed, bare wood such as deck joists, shed rafters and fascia boards. To compare the bees, look at the upper surface of the abdomen: Carpenter bees are bare and shiny black; bumble bees have a hairy abdomen with at least some yellow markings.
Carpenter bees bore perfectly round holes the size of your finger into the surface of bare wood. The tunnel turns and follows the grain of the wood for several inches. Inside the tunnel the female places pollen on which the larvae feed. New adults emerge in late summer.
Coarse sawdust the color of fresh-cut wood beneath the entry hole is a common symptom of activity, as are the burrowing sounds you may hear from within the wood. Female carpenter bees may excavate new tunnels for egg laying, or enlarge and reuse old ones. The extent of damage to wood that has been used for nesting year after year may be considerable.
Bare, unpainted or weathered softwoods are preferred, especially redwood, cedar, cypress and pine. Painted or pressure-treated wood is much less susceptible to attack.
For more information on carpenter bees I recommend University of Kentucky Extension EntFact # 611.
The map below shows the reported distribution of carpenter bees in Iowa as of June 18, 2010. If you see or hear of carpenter bees in your county, please drop us a line (email address: insects @iastate.edu).
Reported Distribution of Carpenter Bees in Iowa, 2010