Yesterday afternoon the outside temperature went up to 35° C (95° F). During that time the birdbath in the backyard was quite popular with the local wasps. There were 2 species. Soon after I posted their photos on BugGuide (here and here), they got identified as Polistes dominula (or dominulus), the European paper wasp (the yellow-banded one) and Polistes fuscatus, the northern paper wasp (the darker one with red marks). The former has been introduced to North America from Europe or Asia.
I noticed that the European paper wasps (above) could land on and take off directly from the surface of the water. The northern paper wasps, on the other hand, seemed to prefer to land on the wall of the bath right above the meniscus. As you can see in the picture below, they support themselves by pushing against the surface of the water with their front legs.