Carpenter bees are large black solitary bees that resemble bumblebees, unlike bumblebees with bare, shiny backs. Carpenter bees lay their eggs in woods, whereas honey bees breed in hives. Their holes are a quarter-inch in diameter and precisely circular. Carpenter bees prefer softwoods like cedar, redwood, and cypress, although they will also attack pine and other wood types. Carpenter bees can attack pressure-treated wood as well. Coarse sawdust can be seen flowing out of the hole and piling up beneath the bee as it drills into the wood. A carpenter bee can drill a hole a few inches deep in just a few hours, which means a large number of holes can be seen in a short amount of time.
The most active period for carpenter bees is early spring when male and female bees emerge from old nest tunnels after spending the winter there. The female bee drills into a suitable spot after they have partnered and married, while the male stays nearby to guard off intruders. Carpenter bees' aggressive behavior often frightens people, yet because they lack a stinger, they are generally harmless. Females only use their stingers if they are threatened. The bee will turn and excavate a tunnel down the grain of the wood once the initial hole has been drilled through the surface. This tunnel, which can be several inches long, serves as the cavity where the female lays her eggs. Carpenter bees not only make new holes but also widen old tunnels, which can cause severe damage to a wood part if left unchecked.
Late in the fall, both male and female carpenter bees will clean out old nest cavities where they over-winter. Since carpenter bees tend to return to the same location where they emerged, it's important to take preventative measures to keep them from infesting logs and wood members.
Preventation: Carpenter bee holes should be treated and sealed if you can reach them, as existing holes attract more carpenter bees. Fill the hole with wood putty or Energy Seal right away. Even if the hole appears to be empty, you should treat it since the bee may be resting and, if left alive, would drill back through the plug you've just inserted.
Treatment: One of the most effective ways to prevent carpenter bees is by applying paint on wood because bees don't perceive painted wood as wood. We've noticed that a gloss topcoat on top of a stain behaves similarly to a painted surface in that carpenter bees rarely drill through it. Spraying insecticides containing cypermethrin, deltamethrin, or bifenthrin (Ortho Home Defense Max) on wood surfaces is one approach to discourage carpenter bees from drilling into it.
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