Flying black insect burrowing into hanging planters?

[Emma]

I've noticed over the past few days, there has been a dark colored (black or possibly iridescently dark) flying insect around the size of a bumble bee that flies underneath each of my hanging planters and goes inside of the drainage holes for a little while and comes back out.
It is very fast and I can't seem to get a good look at it. It visits around the same time every day.
It seems sort of round. I don't think I see any sort of stinger.

Any guess as to what it is?

 

[Chuck]

Without a picture a wild guess would be a carpenter bee