There are a couple of big bumble bees that seem to be digging a hole into our deck railing. Why are they doing that? They’re pretty aggressive and don’t want to let us onto our deck! F. C., Hopkinton, NH

First off, I can assure you that they’re not bumble bees. Bumble bees usually nest in ground colonies, not in wood. What you are almost certainly seeing is a pair of nesting carpenter bees (see Is It a Carpenter Bee or Bumble Bee?). Yes, some do look very much like bumble bees – same size and shape and same yellow and black coloration. The primary difference is that bumble bees have fuzzy thoraxes and abdomens while the abdomen of a carpenter bee is black, shiny, and hairless on top.

Here’s the good news about carpenter bee nests:

1. Carpenter bees are not really aggressive, they just pretend to be. It’s the male bee that patrols the nest area while the female does all the nest building work (insert joke here!). He swoops and buzzes at any perceived threat to the nest…but he doesn’t have a stinger (see Male Carpenter Bees Are “In Your Face,” But Can’t Sting!). The female can sting but she is busy, after all, and not aggressive.
2. These bees will be very busy for a few days excavating a nest hole in your deck railing (see What Caused Round Holes in Eaves?). Inside the dime-sized opening are several brood cells, each with an egg and a pollen ball for the hatching larva to feed on. Once the nest burrow is complete and provisioned, the carpenter bee pair move on. Usually the whole process takes less than a week.
3. Carpenter bees, like all other bees, are important and beneficial pollinators and should be controlled only if they are a problem or doing damage.

And the bad news about carpenter bee nests:

1. It’s common to have more than one carpenter bee pair building nests in a desirable area, and carpenter bees often return to the same nest sites year after year (see Yes, Carpenter Bees Can Nest Again in Your Deck). Although the damage from a single nest is mostly cosmetic and easily filled or repaired, holes from a number of carpenter bee nests can be more serious.
2. Carpenter bee larvae that are fattening up inside their nest cells are an invitation to woodpeckers (see The Woodpecker-Carpenter Bee Connection). This is where the real damage happens as woodpeckers hack away at the nest trying to reach the bee larvae inside. If left unmolested, adult carpenter bees will emerge from the nest opening in late summer.20
3. If carpenter bees are doing a job on your home, give Colonial Pest a call. We can treat the nest area and the nests themselves to prevent new bees from emerging in late summer and continuing the cycle. We also have a program to keep woodpeckers from pecking at your house or deck. Give us a call today!