Four-toothed Mason Wasp

The four-toothed mason wasp is a new one on me.  Saw it in the same place I have been doing the bird/bug/flower hike in the morning.  It eats small caterpillars, pollen, and one source says it also feeds on nectar.

This wasp lives mainly in eastern North America, nesting alone in abandoned bee or mud dauber nests. 

I have no clue why it's called "four-toothed".  It's also called carpenter wasp or mason wasp.