Bayou-Diversity (5 August 2018) In my family there are stories about lean times during the Depression when rabbits were a welcomed source of protein in the household larder. Most were shot at night with the aid of a carbide lantern. Rabbits were detected by their eyeshine in the dim glow of the light. Boys, new to the venture, were reminded that because rabbits' eyes are on the side of their head, only one eye could be seen at a time. And if, when walking through the lonely swamp at night, a person were to detect a creature with two eyes shining, he should remember that such physiology is a trait of many predators that can see much better at night than a mere boy.
The cause of much hope and apprehension during these undertakings was a cluster of highly refractive crystals behind the retinas of the shining eyes. Known as tapetum (ta-PEA-tum) lucidum, these organs make the pupils of some animals appear to glow when struck by an outside light source. Animals with the brightest eyeshine usually have more rods and fewer cones in their retinas resulting in excellent night vision but also color-blindness. Not all animals have a tapetum or eyeshine. Humans don't. Those animals that do have eyeshine tend to be mostly nocturnal and include many mammals but also spiders, some fish, frogs, and alligators. The color of eyeshine also varies by species. Horses have blue eyeshine, fish have white eyeshine, and that of the possum and many rodents is red. The eyeshine of cats and canids, which include cougars and wolves is yellow, a fact not lost on my hungry kinfolks when they spotted two glowing orbs in the heart of the D'Arbonne Swamp.