Carpenter bees

Overview

Carpenter bees, Xylocarpa sp., are large bees that resemble bumble bees. They can be distinguished from bumble bees by their shiny black abdomens with yellow hairs only on the first abdominal segment. Bumble bees have yellow hairs on other abdominal segments as well. They are solitary and do not form colonies. Males have a white- or cream-colored spot on their head between the mandibles that looks like a “nose”. Carpenter bees are pollinators and therefore are considered beneficial. They can, however, damage untreated wood, especially cedar, around the home and garden where they excavate tunnels in which to rear their young. If they are not in a place where they are bothering anyone they can be left alone.

Symptoms and Diagnosis

Carpenter bees excavate tunnels, 4-6 inches long and about ½ inch in diameter in rotten or soft, untreated wood where females lay their eggs and the young develop. Additional damage can occur when woodpeckers peck holes in the wood in search of the developing larvae. The first sign that you may have a problem with carpenter bees is when they fly close to your face when you are close to their nest. Males may appear aggressive but they can not sting. Females can sting if handled.

Life Cycle

Carpenter bees go through complete metamorphosis. Adults emerge from the pupal stage in August or September, feed, and then return to their old nests where they overwinter. They emerge in April and mate. Females lay eggs in existing tunnels or seek out new locations. Females have strong mandibles which they use to excavate tunnels in softwoods, such as cedar. They can advance a tunnel by about 1 inch in six days. They lay an egg and pack in pollen and nectar to feed the larvae, seal the cell, and then start another cell. A tunnel will contain several cells. After the female completes egg laying she dies. There is only one generation a year. Adults live only one year.

Integrated Pest Management Strategies

1. Prevention. Keep all exposed wood surfaces well painted with a polyurethane or oil-base paint to deter attack. Wood stains will not prevent damage. Consider using aluminum, asphalt, vinyl, or 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.

2. Mechanical measures. When dealing with carpenter bees, it is preferable to locate tunnel entrances during the daytime, but treat after dark on a cool evening when carpenter bees are less active. Males lack stingers but female bees can inflict a painful sting if disturbed when provisioning their nest. Wear protective clothing to avoid any stings during treatment.

Deny carpenter bees access to their galleries by sealing each entrance hole. Thoroughly plug the hole with a caulking compound, wood putty, or a wooden dowel affixed with wood glue. If possible, also fill the entire gallery system with a sealant. 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.

3. Contact a professional if structural damage is occurring. Most treatments available are registered only for use by licensed applicators. 

Organic Strategies

Strategies 1 and 2 are strictly organic approaches.

Pesticide Disclaimer: 

Remember, not following the pesticide label before usage is a violation of federal law.