positively glowing

The fireflies flashing in the air are all males. Down in the grass, Dr. Lewis points out, females are sitting and observing. They look for flash patterns of males of their own species, and sometimes they respond with a single flash of their own, always at a precise interval after the male’s. Dr. Lewis takes out a penlight and clicks it twice, in perfect Photinus greeni. A female Photinus greeni flashes back.

- Seduction and Deceit in a Firefly's Flashes