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Factsheet: Least-toxic Control of Carpenter Bees
Pest type: Insects
Carpenter bees are most often confused with bumblebees. They are large, about 1 inch (25 mm) long and have a noticeably hairy thorax and legs, but a hairless abdomen. The abdomen is metallic or iridescent, and may reflect blue, blue-black, bronze, purple, green or buff, depending upon the species.
Carpenter bees have distinct preferences for certain species of softwoods, and do not attack wood that is soft due to decay or tunnel in wood with bark still on it. Their favorites include southern yellow pine, white pine, California redwood, cedar, Douglas fir, and cypress. They chew with their mouthparts into structures, most frequently attacking roof trim and siding, exterior columns, steps, decks, and porch beams and railings. Their entrance is usually against the grain, except where it starts on the end of a board. Approximately 1 inch into the wood, the tunnel turns abruptly at a right angle, and, in newly excavated areas, travels with the grain from 4-6 inches. Several bees working together over a period of time can form a system of galleries extending as far as 6-9 feet into the timber.
The threshold (the number of carpenter bees necessary to generate concern and action) for carpenter bees depends on the wood that is being damaged. If the bees are chewing on a piece of wood with little value, the threshold would be higher than if the damage was being done to a historic home.
Carpenter bees should be protected whenever possible; they are valuable pollinators and do not pose a threat to humans. They tunnel very slowly and their damage is very easily curbed.
They fly and hover with little regard to human activity. Males cannot sting and pose no threat to humans, though their interactions are noisy and may seem threatening as they defend and challenge each other over their territories. Females concentrate on provisioning their nests and are most often seen entering and emerging from large entrance holes in wood or in flowers searching for pollen. They can sting, but won’t, although they may bite if handled roughly.
Do not build external structures with unpainted and unvarnished wood that carpenter bees find attractive. Roof trim, siding, exterior columns, steps, decks, porch beams, and railings are all possible nesting grounds. Keep exposed wood in vulnerable areas covered with paint or varnish, or metal or fiberglass materials.
Fill depressions in wood, which will attract female carpenter bees, before painting. Repaint as often as necessary to keep up with weathering, paying particular attention to undersides of siding and trim.
Woodpeckers and other birds are common predators of young carpenter bees, so make efforts to promote beneficial birds in the area.
When a nest is detected, seal it off or replace the damaged wood. After the bees have emerged, plug holes in wood with steel wool and staple on metal screen. Soft material such as wood putty or caulk will not prevent bee re-entry. You can also use aluminum, asphalt or fiberglass materials. The best time to physically renovate the structure is in the spring after the bees have left their nest.
Attract woodpeckers and other birds, which often feed on carpenter bees, to your landscape.
Look at your product labels and try to avoid products containing those chemicals listed below:
(A = acute health effects, C = chronic health effects, SW = surface water contaminant, GW = ground water contaminant, W = wildlife poison, B = bee poison, LT = long-range transport)
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