Wildlife Spotting

I found this cocoon attached to a wall. It seemed very fresh, and was made with what looked like silk lines. It was translucent, and it was possible to see a green larva or caterpillar inside it. Interlaced with the silk lines there was what looked like black spines. My guess is that, when building this cocoon, a caterpillar added its urticating hairs to it, for giving it some protection. But of course, I am open to suggestions...