Purdue Extension Service

Vanderburgh County, Indiana

Carpenter Bees

By Larry Caplan, Extension Horticulture Educator, Vanderburgh County, IN

For the Evansville Courier and Press, June 14, 2009

For the last two weeks, I've talked about various insect pests. I find myself needing to do so again, for a pest that's been a problem for the last several years: carpenter bees.

Large, black bees are hovering around and drilling holes into homes, out-buildings, wooden furniture and decks. They resemble, and are often mistaken for, bumble bees. The most notable difference is that the carpenter bee has a black, shiny abdomen, compared to the hairy and often yellowish abdomen of the bumble bee.

In nature, carpenter bees will usually chew tunnels into dead tree limbs to build their nests. In more urban areas, though, they will frequently attack bare, unpainted and weathered softwoods including redwood, cedar, cypress and pine. Harder woods and those pressure treated or painted are less attractive to carpenter bees.

What you will see is a one-half inch hole chewed into the wood. The tunnel then turns on a right angle and follows the wood grain for 6 or 8 inches. The female creates separate cells within this tunnel, and places a ball of pollen and one egg in each. The eggs hatch in midsummer, and the larvae feed on the pollen. Adult bees will emerge from the chambers in the fall. These adults will then either create new holes or enlarge holes made previously in order to pass the winter within them. Only one generation exists per year. Carpenter bees then emerge again in April and May to repeat this cycle.

The damage to the wood isn't immediately severe, although several years of attack can weaken the wood considerably.

Although they look scary, carpenter bees are usually not dangerous. The males will aggressively patrol around the nests, and will dive at people and pets who invade their territory. This is all bluff, though; males do not have stingers, and cannot harm anyone. The females do have stingers, but since they don't normally defend the nest (like honeybees will), she will only sting if you try to grab her.

There's no really good answer for controlling carpenter bees. Using hardwoods that are less attractive to carpenter bees or making woods less attractive by painting, pressure treating or varnishing is the best preventative control (stain and water treatment products won't do the job). Liquid sprays containing carbaryl (Sevin) or synthetic pyrethroids (such as cyfluthrin or permethrin) can be applied to wood surfaces so that bees die upon landing or boring there.

Hovering bees can be killed by using aerosol sprays labeled for wasp or bee control. Once holes are drilled, an insecticide powder or dust (carbaryl, boric acid or diatomaceous earth) can be puffed into the tunnel opening. The tunnels must be left open for a few days to allow the returning bees to contact the insecticide. Afterwards, the holes should be plugged using caulking, a short dowel or wood putty and then repainted to discourage future use.

For more information on things that are "bugging" you, contact the Purdue Extension Service at (812) 435-5287.