In Australia there’s a spider known as Thwaitesia argentiopunctata, a/k/a the Mirror Spider. Apparently they have cousins in Southeast Asia as well, as photographer Nicky Bay has been shooting them in his home city-state of Singapore. Writes Bay:
For several years, I have been observing the odd behavior of the Mirror Spider (Thwaitesia sp.) where the “silver-plates” on the abdomen seem to shrink when the spider is agitated (or perhaps threatened), revealing the actual abdomen.
At rest, the silver plates expand and the spaces between the plates close up to become an almost uniform reflective surface.