University of Maryland Extension

Carpenter Bees

carpenter bee and stain on siding
Carpenter bee on siding

Carpenter bees are about 1/2 to 1 inch long and robust. They look like bumble bees, but the top of the abdomen is bare and shiny. Bumble bees have a hairy abdomen. Carpenter bees bore into wood particularly porch, garage and shed ceilings and trim, railings, decks, etc. The resulting holes are almost a perfect circle about a 1/2 inch across. Inside the tunnels will branch repeatedly. Carpenter bees do not eat the wood they tunnel in. They feed on pollen and nectar. The female carpenter bee has a dark face and can sting, but seldom does. The male has a yellow face, and may buzz or fly aggressively around your head and home, but cannot sting.
Indications of carpenter bees in a structure may include piles of coarse sawdust-like material below 1/2 inch holes and tan or black stains on structures. The stains consist of waste material excreted by the female bee as she excavates the wood. The waste material turns black with mold as it ages and can stain structures. It should be removed after the bees have been controlled.

The most effective deterrent to carpenter bees are well painted, finished surfaces. Nail holes or exposed saw cuts are attractive starting points for tunnels, especially when not painted or treated. If tunnels are evident, treatment with an insecticide and sealing of the tunnel is recommended. Wasp, hornet and bee aerosols are effective and probably the easiest control materials to use. Apply the aerosol material into the tunnel entrances and along exposed surfaces. Labeled insecticide dusts are also effective when a small amount is puffed into each hole. A week after insecticide application, close the tunnel with a deep plug of wood putty. Apply insecticides after dark. If you choose to apply pesticides in the daylight, wait until the female leaves the nest before application. Treat for carpenter bees in the spring, just as the bees become active or in the late summer.

Carpenter bees are a native species, are not aggressive and are only noticeable in late spring-early summer. Control is not necessary unless they are damaging wooden structures. 

carpenter bee hole
Holes are almost a perfect circle about a
1/2 inch across
 
carpenter bee waste
Stains consist of waste material excreted 
by the female bee as she excavates the wood
 

Additional Information

Publication: (PDF) HG 29 Carpenter Bees

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