Carpenter Bee 101

BACKGROUND INFORMATION:

Twice a year, in the spring and fall, log homes come under the invasion of pesky insects commonly known as "carpenter bees." These insects bi-annually cause cosmetic structural damage by boring holes into timbers, an act that can compromise structural integrity; cause unsightly stains, and attract woodpeckers. However through understanding the physical behavioral characteristics of carpenter bees, corrective steps can be successfully applied to drive away or eliminate these unwelcome house-guests.

Carpenter bees resemble bumble bees, but are distinct in that their abdomen is shiny with fringes of hairs on some segments. Body size normally ranges from 3/4 to 1 inch long and has a blue-black to b1ack color wi1h a green or purplish metallic sheen. The thorax is covered with bright yellow, orange or white hairs and the abdomen, especially on the top side, is black, shiny and bare without hairs. The more visible of the carpenter bees, with white head markings, is the male of the species. Males, despite being aggressive and often hovering in front of people who are near their nest, are incapable of stinging and pose no risk when encountered. However, the more passive female is capable of inflicting a painful sting when provoked or agitated. Females can be identified from males by their unmarked, black heads.

Despite popular conception, carpenter bees do not ingest or feed on wood itself. Rather, females bore into house timbers to create nest sites. Wintering over in abandoned nest tunnels, adult carpenter bees emerge in the spring (April or early May) to feed on nectar and mate. At this time, female carpenter bees set about excavating new tunnels and or clearing out existing tunnels. Although not being and overly social insect, several females often share a common tunnel entry hole (about 1/2 inch in diameter) and nest in the same general area. When boring, female bees will tunnel approximately an inch across the grain of the timber and then turn at a right angle to follow the grain of the wood in a straight line. The only exception for this common tunnel pattering occurs when the entry of the bees is through the end of a board or timber. A new tunnel will extend four to six inches along the grain.

Alternatively, carpenter bees with reuse and, often, enlarge favorable nest sites existing within a home. In the case of an older timber that has been repeatedly inhabited, a tunnel may extend six to ten feet. Further, repeated inhabitation by several generations of bees generally leads to the branching and interconnection of tunnel systems which can cover a significant area. Re-infestation, nest expansion, and their consequent damage may continue year to year if corrective steps are not taken immediately. The amount of damage that can occur is dirctley proportional to the amount of suitable wood available for nesting. Siding and other thin wood, when targeted by carpenter bees, can be completely penetrated, leading to possible rot and moisture problems in the structure. Generally, carpenter bees prefer to tunnel into weathered bare wood. They will, however, attack wood that is stained or thinly coated with paint. Carpenter bees prefer redwood, Douglas Fir, Cypress, Cedar, White and Yellow Pine, but will nest in other types of wood. 

After a nesting site bas been excavated or cleared out, a female carpenter bee will provision the new nest or broad gallery, with a mass of pollen and nectar, upon which she will lay her eggs. With this complete, the gallery is sealed by the female with a mixture of saliva and wood pulp. This process of stockpiling, egg laying and sealing 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 will return to hibernate in existing tunnels just as the generation before them. In the spring, these new adult bees will reemerge and the entire process begins once again.

CONTROL & PREVENTION:

To control existing carpenter bee populations, each nest site must be found and individually treated. Treatment should be in the form of a preventative insecticide or borate additive or a retroactive insecticide or borate dust. Insecticide and borate additives are generally mixed in with stains or top coats to prevent insects, such as carpenter bees from initially damaging the home. Insecticide and borate dust, such as Delta Dust or Armor Guard, has a long term residual effect for maximum coverage of the bee tunnel and will thus resist simply being absorbed into the timber. The purpose of this form of treatment is two fold: to kill adult bees as they travel in and out of the tunnel entrance and, after the entrance has been plugged, to kill adolescent bees attempting to exit the brood galleries after hatching.

HOW TO FIND 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. Other tell-tale signs of a carpenter bee infestation are: 

• Course saw dust like substance, the color of freshly sawed below on surfaces below an entry hole;
• Yellow-brown fecal drips on the wood below the entry hole;

• Woodpeckers landing on the structure and trying to reach larvae in the galleries
• Burrowing sounds from the female bee, this sounds like a vibration on the wood surface.

RECOMMENDATIONS FOR TREATMENT:

To initially treat a discovered nest site; Timeless Wood Care Products recommends Delta Dust. This insecticide has an excellent residual characteristic as well as a relatively fast "knock-down" effect. We recommend that Delta Dust be applied with a professional grade bellow. The use of such a bellow duster decreases chances of aggravating nesting females and increases chances for optimal dust coverage inside the tunnel.

An extension tube may need to be attached to the bellow "duster" to insure that the tunnel is fully coated. After completing an initial treatment with Delta Dust, the nest site should be left open for at least a week before being plugged. This week period will increase the chances of killing the highest number of adult bees and larvae. However, it must be emphasized that the nesting hole site must be plugged to insure complete eradication.

For plugging the nest entrance hole, we recommend the acrylic base Energy Seal. This product will discourage further drilling while simultaneously accepting stain to match the color of your home. When applying Energy Seal only the first 1/4 inch of the tunnel should be filled so that the residual Delta Dust may remain active in the remainder of the tunnel. A low toxicity borate dust may be used in place of Delta Dust, however, while borate products are relatively effective in eliminating carpenter bee larvae, they will usually not affect the tunneling processes of the adult bees. In other words, such products are effective in halting future generations of bees and discouraging adult hibernation but are ineffective in the immediate "knock-down" of active adults.

Another approach, should you be re-staining or recoating a log home is the use of a borate (Shell Guard or Armor Guard) or "NBS-30” additive with a stain or top coat. Borate additives have a preventative effect similar to the retroactive effect of borate dust; while carpenter bees larvae are eliminated, tunneling adults are not. Similar to preventative borate treatment, "NBS-30" is an insecticide that will bond with applied coatings. Overall, “NBS-30" appears to be 80% effective in discouraging insects which interact and/or damage wood surfaces. Under ideal conditions, "NBS-30" additive is effective for up to three years­

However, caution must be given because Delta Dust and NBS-30 are insecticides that are extremely hazardous to humans and domestic animals when improperly used or accidentally exposed. Protective gloves and face mask must be worn when working with either chemical product. Further, all instructions and precautions provided for each product should be carefully read and followed to prevent negative health effects. 

INSECTICIDE DUST TREATMENT INSTRUCTIONS 

• Read and follow all instructions on the products supplied in kit
• Wear the supplied latex gloves and face mask when loading and dispensing insecticide at all times.
• Fill bellow "duster" 2/3 full of either Delta Dust or Armor Guard dust insecticide and replace rubber filler cap on duster securely
• Insert the nozzle or extension tube into the area to be treated and gently pump the bellow duster, coating the nest with a liberal amount of dust insecticide (should the dust become clogged, remove the brass screw on the bellow duster plug and use the cleaning extension attached to the plug to clean out any clogs from the nozzle).
• When interacting with the insecticides avoid inhalation or contact with skin, eyes, etc. Always stand upwind from area you are dusting. Also avoid exposing plants and animals to insecticide dust.
• After a week reapply dust to holes and plug 1/4 inch deep with Energy Seal.