What kind of nest is this? Photographed in the lower level of the National...
What kind of nest is this? Photographed in the lower level of the National Archives facility in College Park, MD - surrounded by woods on University of MM property. There are a lot if them and I have additional photos but could only load one here.
Prince George's County Maryland
From your photo this looks like a mud dauber wasp nest. The wasp is not aggressive. Knock down the nest if located in an undesirable area. See our Plant diagnostic Website for more information http://plantdiagnostics.umd.edu/level3.cfm?causeID=1031