It's always interesting to get inquiries from people about bees hovering around their decks, gutters or siding. Some are amazed to find perfectly round 3/8" holes that look as if a vandal had done damage. This little "vandal" is a carpenter bee. A carpenter bee looks similar to a bumble bee. Here are the differences between the two:
- Carpenter bees have a shiny black, hairless upper abdomen surface with yellow colored hairs on the mid-section or thorax while bumble bees have a hairy yellow upper abdominal surface
- Carpenter bees nest in wood whereas bumble bees nest in the ground
Though carpenter bees are very large and intimidating, unlike their wasp relatives (hornets and yellowjackets), they are not generally aggressive. Though capable of stinging (females only), these insect don't usual sting unless provoked. The males may hover around and intimidate people as they pass.
Carpenter bees are very interesting in that they will enter primarily unpainted softwoods such as pine and chew that nice, 3/8" entry hole. After chewing a relatively short entrance, the bee will chew another tunnel, several inches long at a ninety degree angle to the opening. Here a female will lay eggs starting from the back, working toward the gallery opening. These bees nest inside of the wood. There is one generation of these insects annually with most of the activity in the Spring. These bees are known to return to previously used galleries from year to year although other bees can make new galleries as well.
The most common sites for these intruders include fascia board (often behind the gutters), deck railings, unpainted lawn furniture, posts and unpainted playground equipment.
Carpenter Bee Management
Some people don't mind these insect that much. As with other bees, they are beneficial as pollinators of flowers. However, other people are not as happy to have carpenter bees around and seek ways to eliminate them.
There are three ways of dealing with the problem: pesticides and repellants and exclusion. The most effective type of pesticide application for existing, active Carpenter Bee galleries is dust. Unlike liquid products which are absorbed into the porous wood, surface, dust remains on top of the wood and available for the insect to contact. Another big advantage of dust is that the application is targeted for this pest within the gallery with little impact on non target organisms such as people, pets and other animals and insects.
There are several such products available on the market for this problem. The best are non repellent products such as carbaryl (Sevin) dust. We sell Apicide, a carbaryl dust product for those wishing to treat the problem. This product may be applied into the entrance of active carpenter bee galleries. Only a small amount is needed for each gallery opening.
For overall control around a structure, commercial applicators are best equipped to apply insecticides that will repel and kill carpenter bees. There are a couple of active ingredient, cypermethrin and lambda-cyhalothrin, which are sold as Demon Max, Cynoff EC, Demand CS and other trade names. These products are applied to exposed wood areas such as along soffits, under gutters or other vulnerable areas. This type of application is helpful where there are a lot of Carpenter Bees hovering around and the targeting of individual gallery openings is not practical. These products are restricted items which we do not offer for sale to the general public. We recommend that they be applied by a commercial pest control/pest management professional.
Another options is to apply a repellant called Outlast NBS 30 which contains several plant oils that naturally repel carpenter bees. The product can be mixed with water for short term control, but for best results, it should be mixed it into paint, stain or sealant (e.g. Thompson's Water Seal©. When applied as directed, this product will repel insects such as Carpenter Bees for for two years or longer. Outlast NBS-30 should be applied to all vulnerable areas to prevent damage to the wood. Targeting the areas where insects return year after year may be a good long term control strategy.
Finally, exclusion can be used after there is clear evidence that galleries are not longer in use. Because of the nature of carpenter bees, it is best to seal inactive openings toward the later part of the spring season sometime in late May or early June because carpenter bees may deposit eggs within the galleries as summer approaches. Sealing the holes late may result in new openings appearing as the young hatch out later in the year or next year after over-wintering within the wood.
Exclusion includes sealing the holes with wood putty or caulking and then painting or applying a polyurethane coating to the wood. Note that the coatings are merely deterrents so that one cannot be certain that bees will not attack the wood again. Where possible, wrapping wood with aluminum flashing is a good deterrent. Plastic siding may be used to cover wood siding to prevent infestation by carpenter bees. Wood-like plastic boards may also be used in place of structural wood such as fascia to discourage damage from carpenter bees.
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