The carpenter bees are the most common wood boring bees that people see. The carpenter bees are in the family Anthophoridae. They attack wood siding, eaves, windowsills, decks and railings, and even patio furniture. Some of the leafcutting bees in the family Megachilidae have been known to attack siding on homes and barns.
The wood boring bees make a half an inch hole in the wood. When the hole is an inch deep, the bee turns the tunnel to follow the grain of the wood. The tunnels are normally 5″ or 6″ deep. Sometimes several female bees work together to extend old tunnels from previous years. Scientists have found wood-boring bee tunnels that extended more than 10' into the wood.
The wood boring bees can deface a home with their tunneling. Many times several bees make their tunnels in the same area. If they are allowed to work undisturbed, after a time they can cause structural damage.
The female bee places a small supply of pollen and nectar at the end of the tunnel. She places an egg next to the food and seals the chamber. She makes a second chamber beside the first. By the time she has finished, she will have built a series of egg chambers. When the last chamber I built, the female bee leaves.
When the eggs hatch, the larvae will eat the food that was provided. The larvae develop inside the chambers. When they have matured into adult bees, they break the partition that sealed the chamber and come out. They find mates and start the cycle again.
Insecticide can control these wood-boring bees. Dust or wettable powder insecticides are most effective because they do not soak into the wood. Insecticide must be injected into each tunnel. The challenge is to make the application without spilling any insecticide on the surface. There is also a risk of insecticide splashing back into the face of the person making the application. Many people prefer to have a pest control professional make the treatments.
After the treatment, the homeowner should wait a few days before sealing the holes. The adult bees can be exposed to the insecticide by crawling in and out of the tunnels. The new bees will be exposed when they hatch.
Caulking or wood dowels are good for plugging the holes. It is not clear whether painting wood actually prevents wood boring bees from attacking. Scientists agree that wood-boring bees are less likely to attack painted wood than bare wood.