The spider with the green spot is a male. The other one is a female and they’ve just mated. Now she’s killing and eating him. No great surprise. They are spiders. What is really rare, probably unique, is that males of this species, Pisauria mira, usually tie up the female before copulation. Researchers at the University of Nebraska, Lincoln, thought this kind of bondage, unknown in other species, might be a protection against cannnibalism. But they weren’t sure. In the wild, it seems, males always wrap the females’ legs in spider silk. So they ran tests in the lab, blocking the silk producing spinnerets of some males with dental silicone. That’s the green stuff. For others they dabbed them with the silicone, but didn’t block the spinnerets. As expected, the males who were able to tie up their mates had more successful matings, and a much better chance of escaping with their lives.