Carpenter Bees

Injury:

Carpenter bees bore into wood to make a home for the young. Bees may drill a large number of 1/2 inch diameter holes (in the case of Xylocopa virginica, a common species in the Northeast) in preferred sites. Often the same nesting sites are used year after year, and the same tunnels reused. The damage is primarily to fascia boards. Nail holes, exposed saw cuts and unpainted wood are attractive nesting sites to these insects. Porches, garages, shed ceilings and trim, railings, roof overhangs and out of doors wooden furniture are common nesting sites. Continued borings may weaken some wooden structures and the yellow "sawdust and pollen" waste materials may stain cars, clothing or furniture.

Behavior:

The males are territorial and in the spring they often guard the potential nest sites. They discourage intruders by hovering or darting at any moving thing which ventures into the nesting area. This can create a "human annoyance" factor and it is one that often startles and concerns the homeowner. Males do not sting.

Description:

Carpenter bees are large black and yellow insects about one inch long that closely resemble bumblebees (Fig. 1). The thorax is covered with yellowish hairs and the abdomen is a shiny black without hairs.

Life Cycle:

Carpenter bees nest in dry wood and occasionally hollow stems. They overwinter as juvenile adults in the tunnels from the previous year. Those that survive the winter mate in the spring (April to June) and then begin nesting activities. They often refurbish old tunnels in preference to boring new ones. The tunnel may be a foot or more in length. The eggs are placed in cells in a tunnel constructed by the bee (Fig. 2). In each cell the female places nectar and pollen she has gathered from flowers as provisions for the young. The larvae hatch and feed on the pollen and nectar and then pass through the pupa stage. New adults emerge before cold weather sets in during the early fall.

The female carpenter bee, like many other bees, can sting but it is uncommon for her to do so.

Management:

Remember, carpenter bees are pollinators and therefore considered beneficial. If they are not in a place where they are bothering anyone, they can be left alone. The majority of the tunneling damage is just to fascia boards. Some people remove the boards with the bees in them, placing them out of the way, and replace with new boards. New boards should be painted or finished promptly to discourage carpenter bees taking up residence.

Well-painted finished structures are a deterrent to carpenter bees. Sometimes, however, the bees persist and it is necessary to treat. Treatment with an insecticide and sealing of the tunnel is recommended. Treatment is usually best done before nesting activity gets underway - nesting and the rearing of young occurs in the late spring or early summer in most years. Treat when the bees are seen early in the spring.

Some commercial wasp and hornet sprays list carpenter bees on the label, and are effective and easy to use. The material should be applied after dark on a cool evening (when the bees are less active) to the tunnel entrances and along exposed surfaces. A few days after application, if no activity is observed, the holes should be plugged deeply with putty or caulking compound. If the tunnels are plugged without first killing the insects, carpenter bees trapped inside will bore new openings.

The active ingredients in some labeled pesticide preparations may contain the insecticide Baygon, cyfluthrin or deltamethrin, permethrin, or tetramethrin.

Boric acid and deltamethrin may also be available in dust formulations - and the dust is puffed into the nest opening (the round hole in the wood), so that bees passing in or out come in contact with it. Boric acid is considered a low toxicity insecticide, but it may be difficult to find homeowner formulations labeled for carpenter bee control. Some people feel they get better results with the dust.

With Baygon, the manufacturer recommends sealing openings with small pieces of stainless steel wool after spray application.

Whatever the treatment that you choose, after activity is no longer observed, repairs should be made to the wood.

Reprinted from Carpenter Bees prepared by Carolyn Klass, Sr. Extension Associate, and Edgar M. Raffensperger, Professor, Department of Entomology, Cornell University, 6/72. Slightly revised by Carolyn Klass, 4/05.

This publication contains pesticide recommendations. Changes in pesticide regulations occur constantly and human errors are still possible. Some materials mentioned may no longer be available, and some uses may no longer be legal.

Recommendations and pesticide use may vary depending on on which state you live in.

Read the label before applying any pesticide.

TK: 2/2007

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