Carpenter Bees. How to Stop the Holes in Your Wood

Eastern carpenter bees are large and robust, about 3/4 to 1 inch long. The top of the abdomen is largely bare and shiny black, and the thorax has yellow, orange or white hairs.¹

Bumble bees are the lookalike. They have a much narrower head than thorax, a hairy yellow-marked abdomen and large pollen baskets. They are social and nest in the ground.¹ The bare abdomen is the quick test.

In California UC IPM features the valley carpenter bee. Females are 5/8 to 1 inch and shiny black or metallic blue. Males usually have pale thorax hair, and the male valley bee is golden brown.²

In Ohio, females have an entirely black head and males have yellow or white head marks.¹ Compare the photos above, then read about other bees and wasps if yours is not a carpenter bee.

Carpenter bees are solitary. Each female has her own gallery, although many may share one piece of wood.¹ Adults come out in April and early May in Ohio, and males hover near nesting females.¹

The female makes a round entrance hole slightly less than half an inch wide. She turns 90 degrees and tunnels 4 to 6 inches along the grain at about 1 inch every six days.¹ Each gallery holds six to 10 brood cells.¹

Egg to adult takes about seven weeks. New adults feed from late August and spend the winter in the old gallery.¹ UC IPM gives about 3 months and one generation a year in California.²

The same galleries get reused and extended, since new digging is slow.¹ That is why the damage grows year after year.

• A round hole about half an inch wide in fascia, eaves, decks, railings or siding.¹
• Coarse sawdust on the ground or deck below the hole.¹
• Yellowish to brownish streaks of droppings and dislodged pollen under hidden holes.¹
• Big bees hovering and dive-bombing near the wood. These are mostly males, which cannot sting.¹
• Woodpecker holes in the same board, since woodpeckers hunt the larvae and overwintering adults.¹
• Bees buzzing in and out of an old hole in spring.¹

Look at unpainted wood first. Nail holes and saw cuts can attract them too.¹

The sting risk is low. Males cannot sting and only look scary when they dive-bomb. Females are docile and sting only when handled, though a female can sting more than once.¹ UC IPM says females sting only when provoked or roughly handled.²

The damage is slow. Initial damage is minor and serious structural harm is uncommon.¹ Over years, galleries can reach 10 feet, and linked tunnels can weaken wood enough that it should be replaced.¹ UC IPM says severe damage is rare.²

Woodpeckers can add holes while hunting bee larvae.¹ Carpenter bees are also pollinators of many crop and noncrop plants.²

A bee sting can be serious for the few people with an allergy, so see the main guide for sting care.

Dust works best. Ohio State says pyrethroid dusts such as cyfluthrin, bifenthrin, deltamethrin and permethrin are the most effective and longest lasting option. Treat at night on a cool evening, puff the dust deep into each hole, and wait a few days before plugging so the bees spread it.¹

Surface sprays are a short-term shield. Apply them in early spring before the females dig. They break down in weeks to months.¹ UC IPM agrees on timing, early spring before nesting or fall after adults settle in.²

Do not treat from late spring through summer. Brood chambers are sealed with wood particles that block pesticides, so it does not work. Do not fill tunnels before the bees have come out.²

Ohio State says wood stain does not stop them, and stomach-poison products such as borates are ineffective, since the bees do not eat wood.¹ After the bees die, seal holes with steel wool and caulk or putty, then paint.^1,2 Many of the dusts are sold only to licensed pros.²

One national cost guide puts carpenter bee removal at an average of $794, with a range of $88 to $1,500.³ If carpentry repairs are needed, the total can approach $2,000.³

Repairs are where the money goes. The same guide lists soffit repair at $6 to $20 per linear foot and drywall repair at an average of $512.³

Other things move the price. Hard-to-reach spots such as walls, ceilings and roofs cost more than an easy spot. City work costs more than suburban or rural work.³

Honey bees are a different job. A beekeeper may remove a live hive for nothing, and live removal averages $445.³ Prices are national, so ask for local quotes that name the method.

• Paint or varnish exposed wood. Ohio State says use polyurethane or oil-based paint, and check it as it weathers.¹
• Do not count on stain. It does not prevent damage.¹
• Choose aluminum, vinyl siding or other materials the bees do not damage.¹
• Build exposed parts from hardwoods when you can.²
• Fill cracks and holes in wood. After the bees are out, plug unused holes with steel wool and caulk, then paint.²
• Cover rough timber ends with wire screening or metal flashing.²
• Apply a surface treatment in early spring, before females begin to dig.¹

In Ohio, adults come out in April and early May.¹ Males hover near nesting females while the females drill.¹

Egg to adult takes about seven weeks, so a new generation appears later in summer. New adults feed from late August and then overwinter.¹ The best treatment windows are early spring, before digging begins, and fall, once adults settle in for the winter.²

In California, adults emerge in spring to mate and nest, and there is one generation per year.² New adults come out in late summer, feed and overwinter, often in old tunnels.²

Ohio carpenter bees are the eastern species. They prefer softwoods such as cedar, redwood, cypress, pine and fir.¹ They avoid well-painted or bark-covered wood.¹

Common targets are fascia boards, eaves, gables, decks, railings, siding, shutters and fence posts.¹ The Ohio State fact sheet HYG-2074 is the Extension guide to read first.¹

Dusts for holes are the pro-grade fix. In Ohio, a person who applies pesticides to another party's property for pay needs a commercial applicator license from the Ohio Department of Agriculture.⁴ Category 10a covers general pest control, and a license needs passing exams with a 70 percent score.⁴

UC IPM covers the valley carpenter bee, Xylocopa varipuncta, and its relatives. Females bore into sound wood, and sometimes decaying wood. Nests are tunnels about 1/2 inch wide and 6 to 10 inches deep, split into chambers with an egg and pollen.²

Western species often use oak, eucalyptus and redwood.¹ UC IPM says sound, unpainted wood without bark is preferred, and most hardwoods are avoided.²

UC IPM says insecticide use is generally not recommended under most conditions and is best kept for heavy infestations or high structural risk.² Some pesticides are limited to licensed applicators.² The California Structural Pest Control Board has a Verify a Company or Licensee page.⁵