This is the head capsule of a 4th instar Polyphemus moth. They shed their skin as they grow and the face usually pops off intact. So naturally I have a bunch of wee containers with wee caterpillar faces waiting to be photographed. Why? I don't know, they look pretty cool and there's a decent variety once you start looking.
It's about 4.5mm wide and photographed using a dfa100mm at minimum focus distance plus a raynox dcr250 for about 2x magnification. Same face left and right, it is a composite, plus a focus stacking test of my diy rail, more info in the link for the interested:
And the rail I put together, it's crude but astonishingly works. I've a few more bits and bobs coming in the mail to refine things, I'll probably make a dedicated post when I have more time.