I've been washing a fleece these last two weeks. And of course, you can find all sorts of things trapped in the fleece by the sticky lanolin. Hay, straw, burrs, corn and this...
No it's not a japanese beetle. It looks like one, only on steroids. I have always just called them that, the beetle on steroids. I think it's real name is the June fruit beetle.
I have these at my house, and I purchased the fleece in the state next to me, so I am sure they are local there too. It's hard to get a photo of the very shiny green shell but they are startling to see. Startling too, to be swishing your hand through the fleece in the rinse water and feel something about the size of a pecan. I'm amazed it stayed so intact, it was hard to dislodge from the fleece and you can see the strands still sticking to it.
All in all, I'd rather find nothing in a fleece, but given a choice, I'll take this critter over live moth larva, or sticky burrs.