Carpenter bees are black, solitary bees. They look like bumble bees but with bare, shiny backs instead of hairy backs. Carpenter bees do not create hives as homes but drill into wood in order to lay their eggs. The holes they drill are perfectly round and about 1/4 inch in diameter. They will drill into most species of wood, even pressure treated wood. As carpenter bees drill, you may see sawdust coming out of the hole and piling up beneath. Lots of holes can appear in a short period of time since it only takes a couple of hours for a carpenter bee to drill one hole a few inches deep.
The time when most carpenter bee activity occurs is in early spring when male and female bees come out after spending the winter in old nest tunnels. Male carpenter bees can be aggressive as they try to ward off intruders while the female drills a tunnel to lay eggs, but they are essentially harmless as they have no stinger. Females have a stinger but only use it if molested. In addition to making new holes, carpenter bees also enlarge old tunnels. If these old holes are left unattended for several years, serious damage to a wood member may result.
Both male and female carpenter bees clean out old nest cavities in the late fall where they prepare for the winter season. Carpenter bees tend to migrate back to the same area from which they emerged. To prevent logs and wood members from becoming riddled by these bees, you can take certain measures mentioned below.
CARPENTER BEE TREATMENT
Treatment depends on the time of year and if bees are present. If the female is drilling away when you find a hole, spray a contact pesticide like a wasp and hornet spray or WD-40 into the hole. She will back out quickly and die. Immediately afterwards, you must fill the hole with wood putty or Energy Seal. You need to treat the hole even if it appears empty since the bee may be resting and, if left alive, will drill back through the plug you’ve just made.
If you find carpenter bee holes in late spring or early summer (and it’s difficult to tell if there are bee larvae developing in the tunnels), run a length of flexible wire into the tunnels in order to break through the pollen plugs separating the chambers before spraying a pesticide (or WD-40) into the hole and sealing it up. (If you use WD-40, you need to push the tube into the hole as far as it will go to break through the chamber walls then spray as you pull it out.) The same procedure should be done on holes found in the fall or winter to kill any bees that may be over-wintering.
CARPENTER BEE PREVENTION
Carpenter bees will attack wood that is stained. On the other hand, painted wood surfaces are rarely attacked since the bees don’t recognize it as wood. They seem to rarely drill through a gloss topcoat on top of a stain as it appears to act somewhat like a painted surface. The slick, hard surface may also not appeal to them.
To keep carpenter bees from drilling into wood, spray pesticides that contain either cypermethrin, deltamethrin, or bifenthrin (such as Ortho Home Defense Max) onto wood surfaces. When it comes to carpenter bees, these products act more as repellents than contact poisons. However, this kind of treatment will have to be repeated every three to four weeks as the effectiveness of these applications lasts only about that long. Pesticides should only be used during the peak periods of activity in the spring and maybe again in late fall. Follow label directions, and read and understand any precautions that must be taken when using these products.
(Reference: PermaChink Systems, Inc.)