Many area residents are observing large flying insects resembling hornets that are boring holes into wooden structures around their homes. These insects are carpenter bees. They make these holes for their nests and as places to lay their eggs in the wood. Although they seldom cause major damage, their activity can cause the wood to weaken over time. Also, they leave holes in the wood, stains on building surfaces and unsightly sawdust.
Because of the resemblance to them, carpenter bees are frequently confused with bumblebees. Carpenter bees are three quarters of an inch to one inch in length. Their bodies are covered with yellow, orange or white hairs, and they have black, shiny abdomens. Bumblebees are smaller and have hairy black or yellow abdomens. Carpenter bees build their nests in wood, whereas bumblebees have nests in the ground. Neither will sting unless handled.
Initially, female carpenter bees bore holes that are half an inch wide and one inch deep. Then they turn sideways at a 90 degree angle and bore two to four inches lengthwise. The wood is not their source of food. The purpose of the holes is to provide them with shelter and a place to lay their eggs. One nest is not a reason for concern; however, their continual boring activity can eventually weaken wooden structures.
Although difficult to control, steps can be taken to deter them and reduce their damage. Since exposed wood is more attractive to them, the wood should be painted with an oil based or polyurethane paint. Wood stains provide little protection. Carpenter bees do not attack surfaces that are not composed of wood, such as vinyl siding. Liquid insecticide treatments that are labeled for use on the perimeters of structures can be applied to the surface of the wood to reduce carpenter bee activity. Treatments will have to be reapplied within 30 days since the chemicals start to break down soon after application.
If the bees have already bored holes into the wood, they should be sprayed with aerosol insecticides labeled for flying insect control. Spray directly into the holes in the late evening or early morning when the bees are inside the holes. This insecticidal treatment kills both adult carpenter bees and their larvae. After a day, seal the holes with wood putty or a similar material to prevent re-infestation. Additionally, apply paint or varnish to the repaired surfaces.
Although carpenter bees can be pestiferous, by taking a few simple steps, their damage can be reduced.
Timothy Daly is an Agriculture and Natural Resources Agent with Gwinnett County Cooperative Extension. He can be reached at 678-377-4010 or Timothy.firstname.lastname@example.org.