This week, the question was: What is this on the underside of this crepe myrtle limb?
This is a praying mantid ootheca. An ootheca is a protective structure in which the adult female lays her eggs. It is constructed out of a frothy secretion from her ovipositor that dries into a hard, foam-like material. The ootheca protects the eggs from the weather and predators throughout the winter until the eggs hatch in the spring. Here is a good article with more info.