Spotlight: Beetles playing with light!

Christmas beetles are master manipulators of light. Not only can they be mirrored, shiny, glossy, iridescent and metallic, they can also use nano mirrors to manipulate light to create a polarising effect. While filtering the light, Christmas beetles slow it down and twist it to the left. In other words, the reflections of these beetles are polarised, changing how we see them; in the picture to the right, beetles on the left are how we see them, on the right is through a polarising filter!

With normal glasses for 3D movies, the left lens allows the polarised light to get to our eyes, but the right lens blocks all the polarised light:

Why do they do this? Puzzling….