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Carpenter Bee Prevention and Treatment

Carpenter Bee Prevention and Treatment

Carpenter bees resemble yellow jackets or large bumble bees but their abdomen is black, shiny and without hair. Their body size ranges from 3/4 to 1 inch in length and has a blue-black to black color with a green or purplish metallic sheen. The male carpenter bee has white head markings, and is the most visible of the species. Aggressive, they often hover in front of people who are near their nest, but males are incapable of stinging and pose no risk when encountered. The more passive female is capable of inflicting a painful sting when provoked, and can be identified by their unmarked, black heads.

Twice a year, in the spring and fall, log homes are invaded by these insects. The holes they bore compromise wood’s structural integrity, cause stains, and attract woodpeckers. Carpenter bees do not ingest or feed on wood itself, but females bore into timbers to create nest sites. Wintering over in abandoned nest tunnels, adult carpenter bees emerge in the spring (April or early May). At this time, females excavate new tunnels and clear out existing ones. Several females will share a common tunnel hole and nest in the same general area.

Carpenter bees reuse and often enlarge favorable nest sites existing within a home, sometimes extending a tunnel by as much as ten feet. Repeated inhabitation by several generations of bees leads to branching and interconnection of tunnel systems which can cover a significant area. Re-infestation, nest expansion and their consequent damage continue until corrective steps are taken. Siding and other thin wood can be completely penetrated leading to possible rot and moisture problems. Generally carpenter bees prefer to tunnel into weathered, bare wood but they will attack wood that is stained or thinly coated with paint.

After a nesting site has been excavated or cleared out, a female will provision the nest with a mass of pollen and nectar, upon which she lays her eggs. The gallery is then sealed with a mixture of saliva and wood pulp, and the process of laying eggs is repeated until the female has completed a total of six broad galleries. Adolescent carpenter bees emerge from the galleries in the late summer and return to existing tunnels to hibernate in the fall.

Control & Prevention

To control existing carpenter bee populations, each nest site must be found and individually treated. Treatment should be either in the form of a preventative insecticide or borate additive or a retroactive insecticide or borate dust. Insecticides and borate additives are generally mixed in with stains or top coats to prevent insects from initially damaging the home. Insecticide and borate dust, such as Drione Dust or Armor Guard has a long term residual effect, remaining in bee tunnels instead of being absorbed into the timber. This form of treatment both kills adult bees as they travel in and out of the tunnel entrance and, after the entrance has been plugged, kills adolescent bees attempting to exit the brood galleries after hatching.

How to Locate the Nests:

Check carefully for the entrance holes on common nesting areas such as structural timbers, eaves, window trim, fascia boards, siding, wooden shakes, decks and outdoor furniture. These holes appear about 1/2” in diameter, often have course saw-dust on surfaces below the hole, and most often occur in areas protected from the weather. You may also observe woodpecker damage to the structure as they attempt to reach larvae in the galleries. Burrowing sounds from the female bee, which sound like a vibration within the wood surface, are also signs of active infestation.

Recommendations for Treatment:

To initially treat a discovered nest site, we strongly recommend an application of Drione Dust directly to the entrance tunnel. This insecticide has excellent residual characteristics as well as a relatively fast “knock-down” effect, and is best applied with a professional-grade bellow. The use of such a bellow decreases chances of aggravating nesting females and increases chances for optimal dust coverage inside the tunnel. An extension tube may be needed to insure complete tunnel coverage. We provide this service or can provide materials for the “do-it-yourselfer”.

After initial treatment, the nest site should be left open for a period of 2-weeks before being plugged. This increases the chances for exposure to other bees visiting the nest, and the nesting hole site must then be plugged to insure complete eradication. For plugging the nest entrance hole we recommend caulking with the acrylic base Energy Seal. This product discourages further drilling and accepts stain to match the finish of your home. When plugging the hole, only the first 1/4” of the tunnel should be filled so the residual insecticide can remain active in the tunnel. Alternatively, short pieces of appropriately sized wooden dowel rod (slightly larger diameter than the entrance hole) can be pre-cut and tapped flush into the hole with a hammer.

While existing damage should be treated and sealed, a preventative solution to carpenter bee control includes adding a contact insecticide to the final coat of stain or acrylic top coat when re-staining or re-coating your home. Additionally, any log home that is stripped down to bare wood will benefit from the application of a Borate treatment both a preservative and pesticide. We include these services at no extra charge to our surface refinishing customers.

Caution must be exercised when working with any type of insecticide as they are extremely hazardous when improperly used. Read and follow all label and manufacturers’ instructions when using these products. For assistance, supplies, or log home care services including carpenter bee treatment please contact us.