Moth larvae?

I noticed this cocoon like object on a privet leaf. I don't know if it's a moth, or maybe a spider, responsible. I will try and keep an eye on it. The mysteries of nature!
Lots of large white, red admirals and commas around the privet so that was lovely. Not quick enough to photograph them though!
Very sadly, the swallow nest fell down from the garage eaves. R found 5 dead very young chicks in the nest just lying on the ground.  I read that their nests can be precarious and fall. Very sad.