Dr. Arikawa was working on sensory stimuli of Japanese yellow swallowtails when they discovered that the butterflies have light sensors on their genitalia. They have since found similar light sensors on a number of other butterfly genitalia. Also, I’m not an expert, but it appears the male butterfly in this image is hanging from his dick.

Arikawa, K., 2001. Hindsight of butterflies: the Papilio butterfly has light sensitivity in the genitalia, which appears to be crucial for reproductive behavior. Bioscience, 51(3), pp.219-225.

This is a series of little illustrated factoids about animal reproduction, posted daily. I’d love to hear your suggestions/ feedback. I also post these on my insta.