Carpenter Bees

L-18269-01

Noel N. Troxclair, Jr. and Michael E. Merchant*

Carpenter bees are so named because of theirpreference for nesting in pith (the soft tissuein some plant stems) and wood. Common

throughout Texas, carpenter bees sometimesdamage structural wood.

To control these bees, it is important to be ableto identify them and to know their biology andbehavior. Steps for effective control include pre-venting damage, locating and applying insecti-cides to the nesting sites, and taking remedialaction to prevent further damage.

DescriptionThirty-five species of carpenter bees can be

found throughout the United States and Canada.Most species are rather small and nest in pithyor hollow stems of plants; others prefer rottingor decaying wood. The largest carpenter beesbelong to the genus Xylocopa and range from 3/4to 1 inch long.

Seven species in this group nest in soundwood and can damage structures. Although soft-wood (such as redwood, cypress, cedar and pine)is preferred, they can attack hardwood after ithas been softened by decay or exposure to theelements.

Carpenter bees are usually shiny or metallicblue-black with a greenish to purplish sheen.Some male carpenter bees have yellow areas onthe face, and males of a few species may be par-tially to entirely buff or pale yellow.

Xylocopa carpenter bees closely resemble bum-blebees in size and color. The bodies of bothtypes of bees are mostly covered with yellow,

orange or black hairs. Carpenter bees can be distinguished, however, by the lack of hairs onthe top of the abdomen.

On the rear legs, female carpenter bees have adense brush of hairs, whereas female bumble-bees have large pollen baskets.*Assistant Professor and Extension Entomologist, and Associate

Professor and Extension Urban Entomologist; The Texas A&MUniversity System.

Carpenter bee: Note the absence of hairs on the top of the abdomen.

Bumble bee: Note the hair covering the top of the abdomen.

Carpenter bee nests are easily distinguishedfrom those of other wood-boring insects. Nestentrances are almost perfectly round and, for thecommon carpenter bee, about 1/2 inch in diame-ter. No other insect produces as large an openingwith a perfectly round shape.

Biology and behaviorCarpenter bees spend the winter in nest tun-

nels built by previous generations. Cold weathercauses many bees to die over the winter.Surviving adults usually emerge in April andMay and seek nectar for food.

Within a few weeks after emergence, the adultbees mate and begin building their nests. Duringthis time, carpenter bees are most active andnoticeable. Females are often seen hoveringbelow a nest entrance, waiting for a mate.

Male carpenter bees may fly aggressively atand around people as part of their territorialbehavior. This activity is harmless, however, asmales cannot sting. Females can inflict a painfulsting, but do so only if handled or provoked.

Fertilized female bees generally prepare thenest site. They may clean out and reuse an oldtunnel with no additional boring; lengthen an oldgallery; create a new tunnel from an existingentrance used by several bees; or bore an entire-ly new gallery.

New galleries are formed by boring into thewood at a right angle to the surface. The clean-cut entrance hole is about half an inch in diame-ter and extends vertically into the wood, up toan inch deep. The nest tunnel is then excavatedin either direction at right angles to the entrancehole. Galleries average 4 to 6 inches long, butmay be up to 12 inches long.

After a gallery has been prepared, the femaleprepares a special “bee-bread” to feed her off-spring. To make it, she mixes collected pollenwith regurgitated nectar and places it at the endof the tunnel. The female then lays her egg—oneof the largest in the insect world—on this food.

Finally, she creates a “brood cell” by sealing offthe tunnel end with a disk made from chewedwood fibers.

The process is repeated until a series of six tonine cells have been formed. Each cell containsall the food needed for the developing larva.

The amount of time it takes for carpenter beesto mature depends on the temperature, species,geographical location and weather conditions.The normal development time from egg to adultranges from 35 days to longer than 3 months.

As the adult carpenter bees emerge, they borethrough the other cell partitions and crawl overless-mature siblings to escape from the nest.

After emergence, carpenter beesfeed on the nectar and pollen of manytypes of flowers, often cutting into theflower to enter well-protected nec-taries. Favored flower types includemints, honeysuckles, passion flower,bluebonnets and various otherlegumes.

There are two or more generationsper year of carpenter bees in much ofTexas. In warmer areas of south

Texas, carpenter bee activity and breeding maycontinue throughout the year.

Economic importance and damage

Carpenter bees become pests when they:■ Weaken the structural strength of lumber;■ Cause costly leaks in wooden cisterns;■ Cause aesthetic damage to wood by boring

holes and by leaving stains on wood andpainted surfaces of buildings;

Carpenter bee gallery entrance hole.

Wood damage caused by carpenter bee gallery construction.

■ Tunnel in and damage ornamental plants;■ Threaten and annoy people.Carpenter bees attack telephone poles, wood-

en fences, eaves, railings, doors, windowsills,outdoor furniture, wooden siding and shingles,and other wooden items.

Succeeding generations of carpenter bees con-tinually expand old tunnels or create new gal-leries in the same wood. The accumulated dam-age may be enough to compromise the structuralstrength of lumber.

Over several years and generations, averagetunnel lengths may extend more than 3 yards.When several females use a single entrance hole,the wood may become completely honeycombedand seriously weakened.

PreventionPrevention is the first step in managing car-

penter bees. Problems with carpenter bees usual-ly arise when preventive measures are not taken,or have failed because of weathering and aging.

Although carpenter bees may attack wood pro-tected by a good coat of paint, they are particu-larly attracted to unprotected or exposed wood.Unfortunately for those who like the naturallook of wood, stains provide inadequate protec-tion from attack by carpenter bees. Woodsealants may deter attack temporarily, but asthey deteriorate over time, the wood becomessusceptible.

Oil-based or polyurethane paints or pressure-treated wood is the most effective for discourag-ing carpenter bees from using structural woodfor nests. If maintained periodically, latex paintsusually discourage attacks.

Covering the wood with metal flashing or awire screen may be used as a last resort wherecarpenter bee activity recurs.

ControlWhen control is necessary, find and treat all

the nest entrances. Because piles of sawdust areusually located directly below active nests, lookfor the perfectly round, dime-sized entry holesabove sawdust piles. Or, watch to see where thebees disappear into the wood.

Carpenter bees usually make their entry holesin well-lighted areas with overhead protection.However, if the entry hole is in the open, it willbe on the side away from prevailing winds.

Remove the damaged wood as needed andreplace it with pressure-treated or painted wood.Plug newly excavated nests with hardwood dow-eling or plastic wood to deter additional carpen-ter bee activity and to protect the wood fromfurther deterioration.

For established nests, apply insecticide dustsor sprays into each entrance hole and to thewood surface for several inches around the hole.Insecticide dusts containing carbaryl (Sevin®),pyrethrins, cyfluthrin, or deltamethrin* can beblown into nest entrances with an insecticideduster or squeeze bottle.

Diatomaceous earth or silica gel* desiccantsmay provide temporary control. Also effective inpenetrating nest cavities are aerosol insecticidescontaining pyrethins, resmethrin, or insecticideslabeled for such use.

When nests are out of reach or too numerousto treat individually, limited control can beachieved by treating the wood around entranceholes with a residual insecticide labeled for useon or around structures.

Pyrethroid insecticides, such as bifenthrin,cyfluthrin, cypermethrin,* deltamethrin,* esfen-valerate, lambda-cyhalothrin* and permethrin,are the most effective. Pest management profes-sionals should select wettable powder ormicroencapsulated formualtions for the bestresidual control.

After application, wait 12 to 24 hours beforeplugging entry holes. Waiting a short period aftertreating with insecticide will eliminate returningbees that were away from the nest and any oth-

* Generally available only to pest management professionals.

Sawdust accumulation below carpenter bee entry hole.

ers that might be attracted to the wood. Newlyemerged carpenter bee adults from a completednest will bore out if the gallery is not treatedwith insecticide before plugging.

Female carpenter bees can become aggressivewhen disturbed during nesting activities, so takeprecautions against being stung when treatinggalleries.

Bee conservation: For those who prefer tokeep a few carpenter bees around, try providingan acceptable nesting site as an alternative toyour home or deck. A small bundle of softwoodlumber, such as cedar or redwood, placed off theground in a sunny part of the garden can suc-cessfully attract bees.

Encourage bees to take up residence by start-ing a few shallow holes, using a 1/2-inch drill bit,in the end grain of the wood. Make sure the

wood pieces are wide and long enough to sup-port the nest. Pieces 4 by 4 inches wide and atleast 2 to 3 feet long should provide a roomyhome for your bees.

Other wood-destroying insects or their damagemay be found when inspecting for carpenterbees. For information on those insects, see L-1781, Subterranean Termites; L-1782, DrywoodTermites; L-1783, Carpenter Ants; and L-1784,Structure-Infesting Wood-Boring Beetles.

Insecticide labels are subject to revision, andchanges may have occurred since this publica-tion was printed. Always read the label of a pes-ticide before buying it.

The pesticide USER is always responsible forthe effects of pesticides that are applied. Alwaysread and carefully follow label directionsbefore using a pesticide.