Carpenter bees are large, wood-boring insects that burrow into sound lumber such as rafters, deck joists, fascia boards and other exposed bare wood. Carpenter bees are traditionally thought of as a "southern" insect. However, in the past 20 years their distribution in Iowa has expanded to reach Nevada, Ames and Boone. The current reported distribution in Iowa is shown in the map below. If you see or hear of carpenter bees in a county not yet marked, please drop us a line (email address: insects @iastate.edu).
Carpenter bees look like bumble bees. Both are three-fourths to 1 inch long. Carpenter bees have a bare, shiny-black abdomen, while bumble bees have a hairy abdomen with at least some yellow markings. The behavior of the two bees is much different. 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.
Carpenter bees bore perfectly round holes the size of your finger into the surface of bare wood. Large quantities of coarse sawdust that fall from the nest openings are often the first sign of an infestation. 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.
Limited activity by carpenter bees can usually be tolerated. If treatment is warranted apply insecticide dust or "wasp and hornet" aerosol spray to individual carpenter bee nests. Nesting can be prevented by application of paint or stain.
More details are available in our online article at www./hortnews.extension.iastate.edu