Carpenter bee or bumble bee? How to tell, and why it matters

Every April and May, big bees start hovering around porches and eaves in Southeast Michigan, and a neat round hole shows up in the deck rail. Most people call them bumble bees.

They are usually carpenter bees, and the difference decides what, if anything, you should do.

Carpenter bee, bumble bee and honey bee, side by side

Sizes and nests are from Penn State Extension and the University of Minnesota. Penn State's rule of thumb is simple: if a number of large bees are hovering near the eaves or drilling in wood, you have carpenter bees.

Where each one nests

Carpenter bees nest in wood, but they do not eat it. The female drills a nearly perfectly round hole about 1/2 an inch across, usually against the grain. About an inch in, she turns and tunnels along the grain, and she lays her eggs in 6 to 8 sealed chambers, each stocked with pollen, per Penn State. They prefer wood more than two inches thick, and they go after unpainted wood: doors, window sills, eaves, railings and lawn furniture.

In Ann Arbor, MSU's diagnostician reported whole neighborhoods losing cedar fascia and soffit boards to them. Carpenter bees drill any soft wood, MSU says, but they love cedar and redwood, the same woods builders use for trim because they resist rot.

So round it "appears to have been drilled by your sharpest drill bit."

Michigan State University Extension

Bumble bees nest in the ground far more than in wood. UMN says their colonies are often in deserted rodent nests, compost piles and under things on the ground. A few species nest higher, in tree or wall cavities, or even a birdhouse.

The hole, the sawdust and the stain

Fresh sawdust below a new hole

The stain below an older hole

Look for three things together: a clean round hole, a little pile of coarse sawdust under it, and a yellowish stain running down the wood. Penn State says the bees commonly defecate on the surface right below the opening, and that is the stain.

One bee in one season does little harm. The trouble is that the next year's bees come back to the same tunnels and extend them, and Penn State says that over the years this can cause considerable structural damage.

Do carpenter bees or bumble bees sting?

• Male carpenter bees cannot sting. They are the ones you notice: they hover near the nest, chase other insects, and dart at people who move quickly, per Penn State.
• Female carpenter bees can sting, but seldom do. Penn State says she has to be extremely provoked, as in handled.
• Bumble bees are not aggressive unless you reach into the nest or step on it, UMN says. Like wasps, they can sting more than once.

Bees nesting in the ground

A steady stream of fuzzy bees going in and out of a hole in the lawn or a flower bed is most likely a bumble bee nest. UMN's advice: if you can avoid the spot, leave it alone. The colony dies in the fall. Some common species are done by early August, and the rest by September. A small fence around the entrance prevents accidents.

UMN also points out that about one in three bumble bee species is in decline, and the rusty patched bumble bee is listed as endangered under the Endangered Species Act.

If the insects at the hole are slick, yellow and black, and angry in late summer, they are not bees. That is a yellow jacket nest, and it is a different job. See how to tell yellow jackets, paper wasps and hornets apart.

Honey bees: we call a specialist

We never kill honey bees. If what you have is honey bees, in a wall or in a swarm on a branch, we call in a specialist who can move them.

A swarm looks alarming but, UMN says, is not dangerous under most circumstances. It is a colony looking for a new home, and it usually moves on by itself within an hour to a few days. Stay back and keep others away from it. Honey bee colonies inside buildings are less common, UMN says, and the first step is to have the bee identified.

What to do about carpenter bees

• Treat the holes, not the whole house. MSU and Penn State both say the treatment goes into the gallery openings. Penn State notes that working in eaves and soffits is why many homeowners hire a licensed company for it.
• Do not plug the holes right away. Penn State says the bees need to pass through the treated entrance, and so do any young bees still inside. Fill the holes in the fall.
• Fill, then paint. Once the galleries are dead, fill them with wood putty or dowels and paint or varnish the wood.

Which wood to paint

Carpenter bees want bare, weathered softwood. MSU says painting or otherwise sealing the wood is reported to discourage them. Penn State recommends paint or varnish, and notes that stained wood is not usually protected. The boards to watch are the ones they already use: end grain on deck rails, fascia, soffits and porch ceilings. The bees come back to familiar wood each spring, which is why our carpenter bee treatment starts with the old holes.

Common questions

About this page

Nick Russler, Owner, Honorable Pest Control

Written by Nick Russler, owner of Honorable Pest Control in Ann Arbor, Michigan. The facts here come from Michigan State University Extension, Penn State Extension and the University of Minnesota Extension, all read on September 26, 2026. If something here is out of date or wrong, tell us and we will fix it.