The side of our house seems to attract Organ Pipe Mud Dauber Wasps during nesting season.
One pair of wasps built this impressive structure behind the patio door, beside the bathroom window:
The female wasp built six tubes over the course of an August week, carrying blobs of mud the size of her head and abdomen from sources about 30 seconds away (1 minute round trip). Each blob produces half of one serration around the tube, with a seam running down the middle, and requires 20 seconds to smooth into place. We got tired just watching her!
Each tube has many compartments, each containing a wasp larva and a paralyzed spider, with a mud cap inside the end:
We watched the wasps attack, sting, and remove spiders of a specific size from the corners of our window frames.
The young wasps in the innermost tube may not make it out alive, because they must chew through at least one outer tube before flying away:
Perhaps layering the outer tubes around a central tube makes for a more compact and durable nest, with the possible sacrifice of offspring in the center.
The new wasps will likely emerge next spring.