In recent years, we've seen a major influx of carpenter bees in the northeast. When the weather gets warmer, pest control companies will be fielding calls daily about these insects, usually being mis-identified as bumble bees. Carpenter bees somewhat resemble bumble bees, except bumble bees have dense yellow hairs on the abdomen and large pollen baskets on the hind legs. Various species of bumble bees and carpenter bees are similar in size. Bumble bees typically nest in the ground whereas carpenter bees nest in wood.

   Carpenter bee damage to wood initially is minor, and carpenter bees seldom cause consequential structural damage. However, their repeated colonization of the same wood can eventually cause considerable wood damage. Carpenter bees nest in a wide range of softwoods and hardwoods, particularly if the wood is weathered. Eastern species of carpenter bees prefer softwoods such as cedar, redwood, cypress, pine, and fir. The bees can more easily tunnel through woods that are soft and that have a straight grain. Carpenter bees attack structural timbers and other wood products, including fence posts, utility poles, firewood, arbors, and lawn furniture. In buildings, carpenter bees nest in bare wood near roof eaves and gables, fascia boards, porch ceilings, decks, railings, siding, shingles, shutters, and other weathered wood (Figure 1). These bees avoid wood that is well painted or covered with bark.

   The carpenter bee entrance hole in wood may not necessarily be in an exposed area. For example, the inner lip of fascia boards is a common site of attack. Except for the yellowish to brownish streaks of excrement and pollen on surfaces below entry holes (Figure 2), the damage would likely go unnoticed. Nail holes, exposed saw cuts, and unpainted wood are attractive sites for the bees to start their excavations.

» Prevention

   Keep all exposed wood surfaces well painted with a polyurethane or oil-base paint to deter attack by carpenter bees. Periodically inspect painted surfaces, because the coatings will begin to deteriorate due to weathering, leaving exposed wood that the bees then can easily attack. Wood stains will not prevent damage. Consider using aluminum, asbestos, asphalt, vinyl siding, and similar non-wood materials that are not damaged by carpenter bees. Seal existing gallery entrance holes to discourage carpenter bees that are looking for potential nesting sites.

» Mechanical Measures

   A non-insecticidal management approach is to deny carpenter bees access to their galleries by sealing each entrance hole. Thoroughly plug the hole with caulking compound, wood putty, or a wooden dowel affixed with wood glue. If possible, also fill the entire gallery system with a sealant. Carpenter bee galleries are a critical resource, since the bees spend much of their time inside a gallery, and they require its protective conditions to survive the winter. Bees that are trapped inside a caulked gallery typically will not chew out due to behavioral constraints. This barrier approach has promise for reducing future carpenter bee infestations.
   In new nests, the single female often can be swatted and killed, or she can be captured and crushed or otherwise destroyed. Larvae and pupae can be killed by inserting a sturdy wire into the entrance hole and probing into the gallery as deeply as possible.

» Professional Treatment

   As a preventive, pest control companies will apply an insecticide to wood in early spring before carpenter bees begin excavating nests. The insecticide kills the bees that contact it on the wood’s surface. Similar treatment will also knock down infestations after they have begun. We obtain excellent results against carpenter bees by spraying wood with pyrethroids (bifenthrin, cyfluthrin, deltamethrin, permethrin, etc.).
   Insecticides that act as stomach poisons, such as borates, typically are ineffective against carpenter bees, which do not ingest the wood that they excavate.

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