Wood Pile Surprise

I knew (hoped?) when I began dismantling the wood pile against our shed that I'd find something neat hidden in the damp logs.  As expected there was a midden - piles and piles of cracked acorns eaten by the chipmunks we see darting about the yard.  Inside the wet and rotted wood were sow bugs of all ages, beetles and earthworms.  And then, I saw something unusual.  A lump of mud.  But this otherwise ordinary lump had carefully carved chambers.  And within those chambers, plump yellow pupae nestled peacefully.

One of the chambers contained a dead spider, legs neatly tucked against its body. What insect had engineered such a intricate ball of life and death?

This wonderous sarcophagus was the work of a mud dauber, a type of thin-waisted wasp. I'm not positive, but judging from the nest's location and shape, I believe it was built by a Yellow and Black mud dauber (Sceliphron caementarium).  The female carries mud in her mandibles to a chosen location (they like eaves, wood piles, sheds, etc.) and constructs hollow tubes.  She then plasters them over with additional mud to form a nest.  Each chamber is stuffed with a spider she has paralyzed.  Next, the female lays an egg in each chamber and seals it shut.  The spider will serve as a meal for the developing larva.

An interesting fact:  mud daubers of different species (there are 5 in the U.S.) prefer different spiders.