Carpenter bees can be persistent pests. It is sometimes difficult to get rid of them completely because of the depth and breadth of their excavation galleries, but there are some extermination methods that are fairly effective for carpenter bee extermination.

The best method of treating for carpenter bees is to locate the tunnels during the day and mark them with a piece of chalk. Tie the chalk to a dowel, if it is necessary. Treating the bees is best done at night, during cool weather when the bees are more sedentary, if this is possible.

Tape a piece of red cellophane over a flashlight to create a red light. The carpenter bees are unable to see the red light, but you should have enough light to see the tunnel entrances. If it is necessary to treat the bees during the day when they are active, you will want to first spray them with a wasp or hornet spray containing pyrethrum so you are able to operate as necessary.

Wear protective clothing, to avoid stings from disturbed female bees (male carpenter bees are the most commonly seen, and they do not sting. However, they do dive aggressively at any intruder, and they are very territorial.)

Wearing gloves and a mask to avoid inhaling any insecticide is a good idea. Any clothing you wear during treatment should be laundered immediately, and you should wash well after performing the extermination.

Carpenter bees that have established themselves under eaves or in soffits may cause you to engage the services of a professional who deals with extermination, since it is highly likely that you will be exposed to spray or powder as it trickles down.

A spray insecticide can protect the wood from carpenter bees for short periods of time, especially in the spring or summer, when it’s easy to visibly locate areas of carpenter bee activity. Sprays can be effective as a preventative, although it is important to spray the wood before you note any nesting activity. A preventative insecticide has limited effectiveness for two reasons: 1) It’s difficult to find every exposed piece of wood on a house so that it can all be treated, and 2) Insecticides begin to break down and erode within only a few months or even weeks after application, so that there may not be a lethal dose of the product on the wood when the carpenter bees appear.

There have been some reports of effective results with a microencapsulated pyrethroid with the active ingredient of lambda-cyhalothrin. This is only approved for use by licensed pest control applicators, but does seem to be useful.

There are other pyrethroids, such as bifenthrin, cyfluthrin, deltamethrin, and permethrin that are used effectively against carpenter bees.

To use the powder method of extermination, the powdered insecticide should be injected as deeply as possible into each entrance hole to the excavations. It should also be placed on the nearby wood surfaces. The powder should be allowed to remain in place, undisturbed, for several days so that the incoming and outgoing bees will pick up the poison and bring it into the tunnels.

After two days, you can also plug all entrance holes for added protection.