bumblebee(s?) in my house

Asked May 19, 2018, 4:30 PM EDT

For the last 5 days a bumblebee (or a carpenter bee, are they big and black and yellow too?) has appeared in my kitchen and attempts to exist through a closed window. I open the sliding window and pop the screen, and it flies out. I close it all again. I have repeated this several times.

The kitchen is not near an outside door, but this bumblebee (or more than one?) has been in my house 8 times. I have no idea where it comes from, no obvious entrance, unless perhaps a dog door two rooms away, or perhaps behind a built-in dishwasher there is some kind of cavity or tiny opening to the outside? I've checked the cabinets and under the sink.
What would cause this behavior and would the bee return again and again, or does this mean there is a bumblebee nest in my house wall and each occurrence is another bee? Of note, today is a cold 47F and I’ve seen no bumblebee activity in my kitchen nor in the garden. Thank you, Chris

Adams County Colorado

1 Response

This is curious and it is unusual for you to find multiple bumble bees in a home, particularly at this time of year.

A little background. Bumble bees produce colonies, but they create brand new colonies each year. The only stage that survives winter are fertile female queens, produced in late summer, which seek out protected places to hide through winter. In spring these queens "wake up" and seek a place to start a colony. Usually they will establish a colony in some kind of cavity with a bit of insulation - abandoned rodent burrows are common sites. If the queen is successful in starting a colony she will rear workers (infertile females) that will then take over much of the colony tasks and allow it to grow. (The workers are smaller, sometimes much smaller, than the queen.) Usually bumble bee colonies peak out with several dozen individuals in mid-late summer, at which time there are some new (next year) queens produced as well as some males. At the end of the year the colony is abandoned and, except for the new queens, everything dies out - all the workers, the old queen and the males.

My first guess as to what is happening is that you are seeing a series of queens that spent the winter somewhere within the home and are emerging. Perhaps there was a cavity behind a wall that they found last fall and several decided to use this as a site to get through the winter. And, for some reason - perhaps a blockage of the entrance they used to get behind the wall? - they are exiting into the interior of the home. If this is the case you are releasing different queens, and each will not be returning after you have released them but will be attempting to start their colony somewhere outdoors.

The other possibility is that somehow a colony is established somewhere within the building, perhaps in an old rodent/bird nest that was behind the wall. This would be very uncommon, as bumble bees usually nest in the ground or near the ground and not in walls of homes. Furthermore, at this time of year the bumble bee colonies are very small - consisting of the queen and, at most, less than a dozen small workers.

From your description, of several large bumble bees at this time of year, I suspect the first explanation is far more likely, that what you are seeing are overwintered queens trying to move outdoors but accidentally enter the living area. If so, this should be over very soon as the queens that were indoors either find a way outside or die indoors.

FYI, you mentionned carpenter bees. That might be a possiblity in some areas of the US, but not in eastern Colorado. The large carpenter bees (Xylocopa species) that somewhat resemble bumble bees do not occur in this state except in a small area along the Utah border.