Really Large Oothecum?

I was out walking when I happened to notice a strange thing among the Salvia leucantha that borders a vacant lot in the center of Old Town. It's funny how your perception is influenced by previous perceptions: in this case I had been noticing monarch butterfly activity in some milkweed nearby, and saw a newly emerged adult butterfly fanning its wings on the fence by the salvia, and knowing how mature caterpillars often wander in search of some upright woody stems to pupate on, well, I had caterpillar images in mind as I scanned the sage. At first I thought this was a parasitized or fungus-ridden caterpillar. The attachment at the top resembles the anal prolegs gripping a twig pre-pupally; the thing is the shape and size of a mature monarch caterpillar. But touching it reminded me of the styrofoam texture of a mantis egg case . . . an oothecum. I had not previously seen one this shape or size.

Later on back at home I found an oothecum, not quite as large but similarly shaped, hidden among the parkway shrubbery.

Unfortunately someone pruned the salvia where the really large oothecum was waiting to hatch, piled the trimmings in a heap, and then carted them off to the green waste recycler I presume before I could go back and take another look at it (and maybe clip it off the plant and sneak it home) to confirm its mantis-ness.