OSU Honey Bee Lab

A picture of a carpenter bee.

Carpenter bees sometimes become a nuisance outdoors when they fly very erratically (hover) around the heads of people, causing fear. Homeowners complain not only about the aggressive nature, but about the round holes bored into wood trim near eaves and gables of homes, facia boards, porch ceilings, outdoor wooden furniture, decks, railings, fence posts, telephone poles, siding, shingles, dead tree limbs and other weathered wood. Initial damage is minor, but new tunnels may be excavated and old ones enlarged, causing considerable wood damage. Also, the yellow, coarse sawdust from borings beneath their entry hole contain their waste materials, leaving unsightly stains.

Identification

Carpenter bees resemble bumble bees. They are large, 3/4 to 1 inch long, heavy-bodied, blue-black to black colored with a green or purplish metallic sheen. The thorax is covered with bright yellow, orange or white hairs and the abdomen, especially on the top side, is black, shiny and bare without hairs. It is the males, with white markings on their head, that fly around aggressively, but they are harmless since they lack a stinger. Females have black heads, are docile and rarely sting. They have a dense brush of hairs on the hind legs whereas bumble bees have large pollen baskets and numerous, yellow hairs on the abdomen. Larvae are saclike, white and legless with brown, globular heads that bear small mouthparts. The pupal stage is passed in a silent cocoon.

Life Cycle and Habits

Both male and female carpenter bees overwinter as adults within their old nest tunnels. Adults emerge in the spring (April and early May) and mate. Females provision the tunnels or galleries with bee bread (mixture of pollen and regurgitated nectar), lay an egg on top of the mass and close the cell with chewed wood pulp. She excavates the gallery with her mandibles (mouthparts) at the rate of one inch in six days. The gallery has a clean-cut round entrance hole with sharp edges 3/8 to 1/2 inch wide (dime-sized) on the lateral wood surface. The gallery continues inward for one to two inches, then turns sharply at a 90 degree right angle running in the same direction as the wood grain for four to six inches or up to 10 feet long, if used by many bees. Damage from a pair of bees is slight, but if used by many bees over several years, damage can be extensive.

Each female may have six to eight sealed brood cells in a linear row in one gallery as she backs outward. Larvae develop on the pollen/nectar food mass provided, with the life cycle completed in 30 to 40 days. New adults chew through the cell partitions and emerge in late August. They collect and store pollen in the existing galleries, return to the tunnels to hibernate and mate the following spring. The previous year's adults die. They are not social insects and there is one generation per year.

Control Measures

Infestations are usually first detected by finding large amounts of sawdust droppings on the ground below the area being drilled or by observing bees going in and out of the round, circular holes in the wood affected. These bees attack all species of dried, seasoned wood, preferring softwoods such as cedar, redwood, cypress, pine and fir. Nail holes, exposed saw cuts and unpainted wood are attractive nesting sites. They may refurbish an existing tunnel instead of boring a new one or new tunnels may be constructed near old ones with infestations persisting for several years.

Prevention

Keep all exposed wood surfaces well painted (oil base or polyurethane) to reduce attack. Wood stains will not prevent damage. Aluminum, asbestos, asphalt, vinyl siding and similar non-wood materials will not be damaged. If practical, remove and replace damaged wood with chemical pressure-treated wood to discourage nest construction.

Insecticides

During the daytime, locate tunnel entrances and after dark, on a cool evening when carpenter bees are less active, treat directly into the nest entrance and on a wide area of adjacent wood surface. Do not plug the entrance since bees should be allowed to pass freely to distribute the insecticide within the holes. If tunnels are plugged before bees are killed, they may chew new openings elsewhere. Dust applications are usually more residual and effective than sprays due to the nature of the gallery construction. Even newly emerged bees will contact the dust when leaving the opening. After treatment, some wait until adult activity ceases or until autumn before sealing the hole with caulking compound or wood putty. This procedure reduces wood deterioration and possible future infestation. Be sure to wear protective clothing to avoid any stings during treatment.

Dusts include bendiocarb (Ficam), boric acid (Perma-Dust), carbaryl (Sevin) or pyrethrins (Microcare). Other pesticides, either with some formulations restricted or restricted to be applied only by a licensed pesticide operator or applicator, include bendiocarb + pyrethrins (Ficam Plus), bifenthrin (Biflex), chlorpyrifos (Duration, Dursban, Empire, Engage, Tenure), cyfluthrin (Optem, Tempo), cypermethrin (Cynoff, Cyper-Active, Demon), deltamethrin (Suspend), fenvalerate (Tribute), permethrin (Astro, Dragnet, Flee, Prelude, Torpedo) and tralomethrin (Saga). Homeowners can use liquid sprays of carbaryl, diazinon, propoxur (Baygon), pyrethrins and resmethrin. Always read the label and follow directions and safety precautions.

Disclaimer

This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author, The Ohio State University and Ohio State University Extension assume no liability resulting from the use of these recommendations.

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.

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