Many thanks to Belita for hosting this week. A very interesting theme, with many possible variations!! I had to think about this one for a while and do some searching of my archive. I finally came up with two 'contrast' shots and two 'difference' shots.
1) Contrast 1: Natural contrast of light and dark. Thistles at sunset.
2) Difference 1: Bumblebee (left) and Honeybee (right)
3) Contrast 2: Artificial contrast of light and dark. Candle against dark background.
4) Difference 2: Life and lifelessness. Small plant growing in the cinders of a lava field. Sunset Crater, Arizona.