Sceliphron caementarium (Black and Yellow Mud Dauber).
Size: approx. 20-30 mm. Photo: 07/18/11, 9 am.

This looks like a 'black and yellow mud dauber' (Sceliphron caementarium). These solitary (thread-waisted) wasps build their nests on houses etc. The mud nests consist of several vertical tubes. The species name is the Latin word for mason. The wasps are about one inch long, do not defend their nests aggressively, and stings are reportedly rare. The small image was taken on 05/27/17. 

bug guide: