Every gardener owes a big debt to bees. Bumblebees are some of the world’s most efficient pollinators, and many flowering plants would be in trouble without them. A healthy bee population is an all-round good thing for your yard, and you should do everything you can to encourage them. Well, bumblebees at least. There are some bees you definitely don’t want around, and one of these is the wood bee.
Wood bees, also known as carpenter bees, are closely related to bumblebees and look very similar. The only visible difference is that their abdomen is solid black, without any yellow stripes. Their behavior is very different though. They’re less aggressive – only the females have stings, and they won’t use them unless provoked – but their other habits are very destructive. Bumblebees make nests where between 50 and 400 bees live, usually in old rodent burrows or hidden in long grass. They’re nowhere near as big and elaborate as the hives built by honey bees but they’re still organized colonies with an egg-laying queen tended by workers. Wood bees are more solitary. Each bee makes its own tiny nest, although if you find one there will probably be more nearby. The problem is wood bees live in tunnels bored into wood, and as more of them move in the damage to the wood increases.
Wood bees evolved to live in trees, but they’re not fussy; they’ll colonize any wood. Their tunnels often run along under the surface too, so it doesn’t have to be a very thick piece of wood – an inch is more than enough. Beams, weatherboards, your deck – anything built of timber is a potential home, and if the bees aren’t dealt with they’ll progressively weaken it by boring new tunnels. Some tunnels more than ten feet long have been found, and that means a fair amount of wood has been removed from your home.
Signs of wood bees aren’t hard to spot. They work like giant woodworm, using their hard mouth parts as a cutting tool to drill circular tunnels about 2/3 of an inch wide, so the holes are quite visible. If the bees are attacking something you’ll also find a sawdust-like residue below the holes. If you find these traces watch for a while; if you see bees emerging or landing you have a wood bee problem, and you need to deal with it as soon as possible.
There are a few things you can do to discourage wood bees from setting up home. Keep all exterior woodwork painted. stained or varnished; that isn’t guaranteed to keep them out but it does help. Bare wood is an open invitation to them. The bees do have natural predators and almost any insect-eating bird will snap them up if it gets the chance, but beware of woodpeckers. They’ll happily eat the bees, but they do it by pecking holes into the wood to get at them in their tunnels – and that causes even more damage than the bees do.
Wood bees are very sensitive to vibration, so if you have an infestation you might be able to drive them out by making a noise. Set up a radio next to the affected area, crank up the bass and tune in to a 24-hour music station. This has the advantage of not involving any poisons, but if it doesn’t work you’re going to have to resort to chemical warfare.
There are some very simple ways to kill wood bees in their burrows. The easiest is to squirt gasoline or diesel into the holes – this will kill any bees or larva in there. The downside is you can’t use this method on trees because it will kill them too; obviously there’s also a fire hazard. Carburetor cleaner or WD40 can also be used, and both of these come in spray cans with handy nozzle extensions, but the same issues apply. If you decide to use any of these substances make sure you wear gloves and an approved safety mask – you don’t want to be inhaling them.
A safer option is to use a commercial insecticide; this probably won’t work as rapidly but it doesn’t cause a fire risk and can be used on live trees. Choose a powder insecticide; liquids and sprays can be absorbed into the wood before killing the bees or larvae. Dust the poison into the holes as deep as you can, and leave it there. Bees will pick it up as they enter or leave the tunnels, and if there are larvae beyond the reach of the dust they’ll get a dose when they hatch and leave the nest.
Whatever method you use to get rid of the bees, once they’ve gone you need to prevent them coming back. This is essential; wood bees leave scents in their tunnels that will attract more bees to the same location, and empty tunnels will simply attract new occupants. If you see a wood bee leaving its hole to go foraging you can take the opportunity to shut it out with a temporary plug. Obviously don’t use wood for this, because it will just bore its way straight back in again. Instead roll up a piece of steel wool and jam that into the entrance. You can even do that with the bees inside – eventually they’ll starve to death. Of course there’s a risk that they’ll manage to drill a new exit hole, so avoid doing this if possible.
Steel wool will rust eventually and in any case it doesn’t look great, so you should permanently repair the holes as soon as possible. Seal them with caulking or putty and sand them level with the surface, then give the wood a bee-resistant finish. Any form of wood treatment will help deter bees and keep the timber in good condition, but polyurethane paint seems to be the most effective at keeping them out.
Wood bees can be a real pest, but they’re big enough to be noticeable so you can usually catch them before they do too much damage. The important thing is to seal the holes once you’ve dealt with the bees and keep your woodwork in good condition to prevent them returning. Do that and you can concentrate on encouraging those beneficial bumblebees.