It's fallen off your wiper arm. There's another part to it that hooks behind the wiper blade deflector. It's not uncommon for them to fall off.
Sorry, I should get out more!
I've just replaced mine (£5 from an alfa dealer - it's the same part) - it's a stability arm for the drivers-side wiper. Without it the blade get's a little loose and flops about, especially at motorway speeds.
Mine broke in exactly the same place as emtree's - I guess they get brittle over time an UV exposure.
When fitted the arm points down between the wiper and the wind deflector thingy ;o)