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Carpenter bee infestation guide for buildings:
This article describes carpenter bees (Xylocopa spp. - about 500 species) and how to inspect a building for carpenter bee damage. We explain and illustrate how to identify carpenter bees - what carpenter bees look like, why and where they attack buildings, and how to cure a carpenter bee infestation using pesticides or other methods.
We describe building details that increase the risk of carpenter bee infestation - which tells you where to look for damage as well as how to prevent carpenter bee infestations in buildings without reliance on pesticides.
We also describe how to distinguish carpenter bees from other insect or other types of building damage and how to tell a carpenter bee from other insects. We include examples of building damage caused by carpenter bees. And we provide citations to authoritative sources for more carpenter bee identification & control information.
Early Signs of Carpenter Bee Activity on a Building
Often the first evidence you may see of carpenter bee activity will be a perfectly round hole about 5/16" in diameter in the edge of exterior trim boards at a soffit or fascia (photos further below on this page).
But two very good clues of carpenter bee activity at a building are only slightly more subtle: carpenter bee tracking marks on building siding or walls just below wood trim (photo above) or a neat little pile of fresh sawdust beneath a hole where a carpenter be is busy tearing away at a wooden trim board (photo below).
Look for tracking, sawdust, exit holes, or the insects themselves. But look first for these splashes on building siding that may indicate carpenter bee activity. Two more examples of these bee marks are shown just below.
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Carpenter Bee Entry & Exit Holes in Building Wood Trim or Wooden Structural Members
Those 5/16" to 1/2" perfectly round holes carpenter bees cut into (usually) the edges of wood trim or other exposed lumber are made by the female carpenter bee to prepare a nest, typically six to ten inches deep into the wood.
When carpenter bee damage holes appear in the face of a trim board more often they are oblate, as shown in photo at left.
In these nicely drilled openings into building wood trim or even deck or porch framing, the female carpenter bee deposits eggs that hatch into larvae and develop into young adult carpenter bees, feeding initially on pollen stored in the nest by the parents.
Because carpenter bees like to return to the same nest each year, the length or depth of these nests can become much larger, extending many feet along the interior of wood trim or other boards on building exteriors.
Watch out: Because the holes made by carpenter bees (for purposes of nesting and laying eggs) are so perfectly round and because often you see only those openings they can be mistaken for drill marks. Don't confuse insect damage or holes such as those made by carpenter bees or powder post beetles with mechanically made drill holes in wood boards, beams, or other structural components on or in buildings.
At Drill Marks we show drill marks in wood caused by an amateur pest treatment attempt. While to an experienced eye, holes in wood caused by insects are easily distinguished from those caused by humans using a drill or hammer and nail, on occasion someone is fooled. Below in our photographs of carpenter bee damage to two different buildings we illustrate two cases of holes that are caused by insects, not mechanical events on buildings: powder post beetle holes in wood, and carpenter bee holes in wood.
Both of these examples of carpenter bee damage are old - weather and decay have softened the edges of carpenter bee openings and exits in the wood.
What to Do About Carpenter Bees: 4 options: kill vs. seal vs. replace wood vs. vacuuming?
Unlike more serious wood destroying insects such as CARPENTER ANTS or TERMITES, carpenter bees are solitary insects, so using the term "infestation" to describe carpenter bee activity on a building can be a bit over-stated.
Nonetheless, as our deck photograph above shows, left unattended these bees can eventually cause extensive damage to a building or to a wooden deck or more often its wood trim. Unlike carpenter ants and termites, carpenter bees do not invade deeply into a structure - their activity is usually found on external trim and exposed wood structural members such as the deck above. But you can also see that this deck has been severely damaged.
Avoid killing carpenter bees (or any other bees) if at all possible: Certainly don't kill a carpenter bee out of fear of being stung. Female carpenter bees (shown at left) are capable of stinging but are not aggressive. Male carpenter bees have no stinger.
We don't like to kill carpenter bees unnecessarily as they are solitary insects and as they are important pollinators for some (open faced) flowers. But where an individual is causing a lot of trouble, a quick squirt of insect killer spray into an active carpenter bee-drilled opening is usually enough to send the bee elsewhere (or kill it if it's inside the opening at the time).
Where killing carpenter bees becomes necessary because of an extensive colony and significant building damage, dry insecticide powder blown into nest openings can kill hatching larvae as will an (easier to use) spray insecticide with residual effects. Use a sprayer with a plastic straw-type nozzle that can be inserted right into the carpenter bee nest opening. (Don't spray insecticide in your own face during this operation.)
The University of California Integrated Pest Management Program also recommends using a desiccant dust (diatomaceous earth or boric acid), inserting it into the nest openings. The dust kills the developing insects by a combination of abrasion and drying out. However desiccant dusts remain effective only if the dust stays dry - which may be optimistic when this approach is used on exterior trim openings, especially shallow ones, located in climates subjected to wind-blown rain.
Fill carpenter bee nest holes, seal surfaces: Because carpenter bees like to return to the same nest each year, when the holes are empty, try making the nesting site less attractive by filling existing holes with caulk or hard wood putty, and keep the surfaces of exposed wood coated with paint or a preservative stain.
Replace badly damaged wood: For trim boards that have been extensively damaged (making filling holes inappropriate) we replace the board with preservative treated lumber, making sure to follow the manufacturer's directions for also treating and sealing cut ends of the wood.
In our OPINION, advice of some experts to use hardwood for all exterior repairs is simply not practical - people do not pay for oak boards for soffits and fascias.
Vacuuming out carpenter bees? we have read at least one source who recommends vacuuming out the carpenter bee nest to attempt to remove any bees or larvae - an idea which may sound ecologically sound but in our OPINION is a bit iffy: imagine dragging your shop vac up a fifteen foot ladder and then, in mid-air, trying to suck bees out of a 5/16" to 1/2" hole in the edge of a board. And what happens to people standing on a ladder, holding a vacuum cleaner, when the bees get mad?
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 Jeffrey Hahn, Colleen Cannon, and Mark Ascerno, "Carpenter Ants", University of Minnesota Extension, retrieved 9/19/2012, original source: http://www.extension.umn.edu/distribution/housingandclothing/dk1015.html, copy on file as [Carpenter_Ants_UMinn.pdf]
 Wikipedia provided background information about some topics discussed at this website provided this citation is also found in the same article along with a " retrieved on" date. NOTE: because Wikipedia entries are fluid and can be amended in real time, we cite the retrieval date of Wikipedia citations and we do not assert that the information found there is necessarily authoritative.
Carpenter Bees, retrieved 9/22/12, original source: http://en.wikipedia.org/wiki/Carpenter_bee
Following references 5-7 cited by above.
 Jones, Susan. "Fact Sheet Carpenter Bees". Ohio State University Extension, retrieved 9/22/12, original source http://ohioline.osu.edu/hyg-fact/2000/2074.html
 Minckley, R.L. 1998. A cladistic analysis and classification of the subgenera and genera of the large carpenter bees, tribe Xylocopini (Hymenoptera: Apidae). Scientific Papers, Natural History Museum, University of Kansas 9:1–47. Archive.org. Retrieved 09/22/2012, original source http://www.archive.org/details/cladisticanalysi00minc
 "U.C. Riverside Entomology Research Museum: "Carpenter Bees" Order Hymenoptera Family Apidae, genus Xylocopa". Entmuseum.ucr.edu. Retrieved 9/22/12, original source: http://entmuseum.ucr.edu/bug_spotlight/posted Images-pages/34.htm
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