Do they sting? Are they otherwise harmful? I'm glad holestory asked because I've seen something similar to these on my stone steps leading down to my house. My bugs may the the same ones. I think mine are dark charcoal gray and red. They are pretty.
On the side of the cement(?), it is the red mark with two black stripes at one end - it has a dark shadow above it on the cement. (I believe that the pinkish color up top is the inside of an upper piece of cement.)