I first noticed this mud-dauber wasp nest in my backyard in January. It’s the work of a female black and yellow mud dauber, Sceliphron caementarium. The mud-pellet nest is right outside my back door, on one of the mini I-beams that support the balcony. The nest had probably been built late last summer, or even early fall (I missed the construction process completely!). Eggs were laid along with a cache of paralyzed spiders for the larvae to feed upon when they hatched. The larvae made their own cocoons inside here and metamorphosed into adult wasps.
On Monday, June 13, I noticed three holes in the mud. The wasps were finally digging themselves out. They had emerged either earlier that day or, more likely, over the weekend, while I was out of town. While I was puttering around the Back 40 that afternoon, another hole appeared. On the 14th, there was no activity. On the 15th, another. Ditto the 16th and the 17th. Was one wasp a day emerging? No, because I actually saw one of the inch-long wasps emerge on Friday. It came out of an existing hole. And it came out quickly, dropping down to the metal, and then flying off. Looks like they are ready to rock as soon as they emerge. Too fast for this paparazzo. This morning there were still six holes.
Since the gathering of spiders to stock the nest must take time, I assume the female wasp lays her eggs individually, hence the asynchronous emergence.
And now they’re out there, over Brooklyn. Will one return here to build a new nest this fall? Also of interest: as the blue dauber wasp uses old black and yellow dauber nests for its brood, will this structure find a second use?
Backyard and Beyond 
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