Animal Eyeshine

My house cat Mikey likes to sneak up on me when I'm reading. He gets behind the drapes of the picture window, slinks toward my reading chair, and then, when he's right beside my ear, lets out a meow to let me know he has successfully stalked me once again. When I look at him, his eyes are glowing orbs of silver-green, reflecting the light of the reading lamp over my shoulder. That glow is called eyeshine. It's the same phenomenon our primitive ancestors saw on the predators waiting just outside the circle of light from the campfire. Eyeshine is a feature of nocturnal animals. It's caused by a special membrane behind the retina of the eye that allows them to see better in the dark. That membrane, called the tapetum, is a retroreflector that redirects visible light back through the retina. This increases the light available to the eyes' photoreceptors, enabling night vision. That reflected light also travels right back along the light path to the source, presenting as eyeshine, or glow-in-the-dark eyes. This effect is most commonly seen in deer, presenting as glowing, white eyeshine. The paralyzing deer-in-the-headlights effect occurs because their eyes are already fully dilated, and they are blinded by the sudden abundance of light. The deer react by standing still and waiting for their eyes to adjust. Some folks use this to see or count deer, which are crepuscular creatures —active at twilight, an hour before or after daylight. Poachers take advantage of this to "jack" deer — spotlighting and shooting them as they freeze in place. For this reason, "shining" deer is illegal during the hunting season (September 1 through December 31) in New Hampshire. In addition to all nocturnal carnivores and some mammals, alligators and bullfrogs also have eyeshine. I know this because my cousin in Florida took me gator shining when I was a teenager, and my grandfather took me frog hunting when I was still in grade school. Alligators have red eyeshine and bullfrogs have green. I discovered barred owls also have red eyeshine when I took a flash photo of one. My trail camera's infrared flash photos show me coyotes have yellow-green eyeshine. Eyeshine is also common in some spiders. I discovered the effect when I took my youngest son, a middle-schooler at the time, out in the dark to help blood trail a deer a friend had arrowed. When we got to the point where we were on hands and knees searching out the drops of blood, Devin said, "Hey, look at this." It was a wolf spider with bright, green glowing eyes! The reason we don't always see eyeshine is that our own eyes have to be in that reflected light path. I've walked through the woods using a flashlight held waist level many times and never saw bright spider eyes. But once I put on a headlamp, I started seeing little specks of light on the forest floor. Closer examination showed me those wolf spiders, which don't build webs, but are nocturnal hunters. Wolf spiders are quite common, so try this at home, out in the yard after dark — unless, of course, you have arachnophobia. Cutlines--these game camera photos show deer eyeshine from an infrared flash.