When I returned home and looked it up I realized it was a Spongillafly in the family Sisridae. They are related to lacewings but to my mind the adult looks more like a caddisfly. The larvae live in the stream and feed on fresh water sponges. I was hoping we had sponges in the river but I have never seen them. Anyway the larvae move up onto the side of the bank when they are ready to pupate. So this isn’t an egg sac after all, it is a pupa. This larva crawled out of the water and up onto the underside of this rock where it built this elaborate cocoon.
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