L-1826

Carpenter Bees Philip J. Hamman and John M. Owens

Carpenter bees are common in Texas and ordinarily their tunneling is of little or no consequence.  However structural repairs may be necessary if colonies are present year after year in the same timber. Effective control includes prevention, persistence in locating the nesting site and insecticide applications.

 At least twelve species of carpenter bees occur in the United States. Their nesting activity varies; some prefer rotting decayed wood, others thc pithy or hollow stems of plants. Some species become economically important when they nest in sound structural wood. Carpenter bees which nest in wood generally are large 3/4 to 1 inch long. They are metallic blue-black with green or purplish reflections and are covered with orange or bright yellow hair. Carpenter bees resemble bumblebees in size and coloration except for the top of the abdomen (tail section) which is black and largely devoid of hair. Bumblebees have some yellow hair on the top of the abdomen. Female carpenter bees also have a dense brush of hairs on the hind legs whereas bumblebees have unusually large pollen baskets.

Both male and unfertilized female carpenter bees overwinter in nest tunnels constructed the previous summer. They usually emerge from the tunnels in April or May. Mating occurs within a few wecks and nest construction follows immediatcly.

The fertilized female often cleans out and reuses an old gallery without further burrowing. She may also lengthen an existing gallery or tunnel into wood to construct an entirely new gallery. In establishing a nesting site the female bores into wood at a right angle to the surface. The characteristic entrance tunnel is clean cut 1/2 to 1 inch deep and approximately l/2 inch wide—about the size of a dime. The female bee then turns at right angles and hurrows With the wood grain sometimes as much as 6 to 8 inches in either direction. She collects pollen and mixes it with regurgitated nectar to form a dough-like mass. She deposits one egg on this "bee-bread" and seals off the tunnel with a partition composed of a chewed wood pulp. This procedure is repeated until a linear series of six to nine cells is formed. Each cell contains a food mass for the hatching larva. The complete developmental cycle from egg to pupa occurs in this enclosed cell and the larva exists solely on this food mass.

The time required for development to the adult stage depends on the species of bee geographical location and weather conditions The developmental period ususually is slightly more than a month but it may take as long as three months. Emergence usually occurs in late August or September. There may be two or more generations of carpenter bees each year in many areas of Texas. Continuous generations may occur in south Texas.

Newly-formed adults chew through cell partitions to emerge. In so doing they crawl over immature individuals not ready to emerge. The sexually mature bees do not mate in the fal1 but prepare for overwintering by gathering pollen. Usually little or no nest construction occurs in the fall. Carpenter bees are active in the spring with the female hovering in front of the nest entrance awaiting the male for mating.  Males at this time are very aggressive and menacing when disturbed but fortunately cannot sting. Female carpenter bees will sting only if molested.

Carpenter bees prefer softwoods such as redwood, cypress, cedar, and pine tor nesting sites. Hardwoods occasionally are used, but only after they have been softened by exposure or decay. Damage to structures is usually slight and amounts to only cosmetic defacement.

When subsequent generations expand old galleries, or construct new ones in the same picce of wood, serious damage may result. Abandoned nests of carpenter bees may be inhabited by wasps, ants, other bees and scavengers such as dermestid and darkling beetles. The "little carpenter bees," genus Ceratina, tunnel in pithy or hollow stem plants and may cause damage to certain ornamental plantings. They can be controlled by eliminating the plant or by careful pruning.

Carpenter bee activity is commonly found around wood fences, patio covers, wood Shingles, roof eaves, porch ceilings, doors, and windowsills.  Unfinished wood or wood that is well weathered or poorly painted or stained is preferred for nest construction.

Remove infested wood and replace it with pressure-treated wood Maintain a sound continuous coating of paint or white wash on all exposed wood.  Plug newly excavated nests with doweling to discourage further activity and to protect the wood from deterioration.

If the nest has been completed, apply dusts or sprays of insecticide products containing propoxur (Baygon ®), malathion, pyrethrins, resmethrin, or carbaryl (Sevin ®) into the nest entrance and on a wide area of wood surface around the entrance hole.  Wait 12 to 24 hours after application, then plug the hole. New adult carpenter bees will continue to emerge from completed nests if insecticides are not used before plugging. By waiting a short time before plugging the nest entrance after application bees returning to the nest and those attracted to the wood will be eliminated. Take precautions to avoid being stung while treating carpenter bees.  Females are very
aggressive, particularly during nesting activity.

Insecticide label clearances are subject to changes and changes may have occurred since this publication was printed. The pesticide USER is always responsible for the effects of pesticides on his own plants or household goods as well as problems caused by drift from his property to other property or plants. Always read and follow carefully the instructions on the container label.