By Eddie Ayers, County Extension Agent
Where did this sawdust come from? Who has been drilling into my wood siding? The culprit is a large bee that resembles a bumblebee and is often flying around porches, decks, and eaves of homes as well as boring into wood. These insects are known as carpenter bees.
Adult carpenter bees are large, one inch (or slightly longer) robust insects. They are blackish in color with yellowish hairs mostly on the thorax. The abdomen is shiny black and is bare of hairs on top. This helps to distinguish it from bumblebees that are similar in size and coloration, but bumblebees have yellowish hairs on top of the abdomen. The eggs, larvae, and pupae are seldom seen since they are out of sight in cells within galleries constructed in wood.
The carpenter bee becomes destructive by tunneling into solid wood, things like poles, fences, and buildings. The tunnels may extend to a depth of a foot or more and are divided into cells by partitions made from sawdust or plant fragments cemented together by saliva. The food for the young is primarily pollen. These bees, which are not aggressive, are a nuisance from spring on into early summer. The female can sting when cornered, but the male cannot sting.
Controlling carpenter bees can be a challenge. Wood surfaces painted with oil-based paints are not attacked, but you must do a thorough job of painting all of the exposed wood. They are able to find the tiniest of areas not painted. Because they are so big, you can kill them by swatting them with swatters or rackets when they fly by, but that is time consuming and not very efficient.
There are several insecticides that are recommended for treatment of carpenter bees. Most “ready to use” insecticides will kill them when applied directly to them. Another option is to treat the nests directly in late evening when all the bees have settled in for the night. Spray the insecticide into the hole that leads to their nest. New on the market is a foam containing prallethrin and lambda-cyhalothrin.
Two things to keep in mind when treating carpenter bees, first most of the insecticides that will kill them are toxic to all types of bees. Also, even though they cause property damage, carpenter bees are pollinators and if they are not boring into your house you may want to leave them alone. If you use insecticides, remember to read and follow the labeled directions and you will probably need to treat the area every two weeks. For extra control, apply petroleum jelly, wood putty, a dowel, or even gum over the hole after treatment. This will make it harder for them to escape. Do not cover the hole during the day as they will bore another hole next to it when they return to the nest.
There are also several traps on the market, but there has not been enough UGA research to determine which one works best. One tip that I have heard about is that if you are using a trap, it works better if you put a dead bee in the trap first. It seems the other bees come to see what is wrong and get caught. If you have one that has worked, please let me know.