I had left a small plastic pot overturned on top of small post next to the garden, and when I took it off a few days ago, I discovered this lady and her babies beneath it. (Click the photo to see her larger.)
She is a European paper wasp, a new and rapidly spreading arrival in Colorado (first spotted here in 2001). I found this out thanks to a helpful Colorado State University Extension fact sheet written by Whitney Cranshaw, the don of Colorado creepy-crawlies.
This fertilized queen spent the winter by herself in some sheltered spot, then started building her nest, making paper from wood that she had chewed to pulp. Her little colony will grow throughout the summer, then die off next fall, leaving behind a few more queens to start the process anew.
To give you an idea of her size, that post is just 1.5 inches square. I marked it with an arrow in the photo below. Please ignore the rest of the mess that is my garden.
I'm debating whether to let her stay there. Unlike yellowjackets (which look a lot like her, but fatter), she is not a scavenger, preferring to feast on caterpillars and other insects, many of them garden pests. But as her brood grows, I fear the wasplets may become more defensive of that space, which you can see is right next to the garden faucet. I also wonder if wasps eat honeybees.
I guess I'd better get more info and make a decision soon!