Have you ever gone out at dusk or after dark with a flashlight and shined it into the woods or the edge of the lawn or bushes in your yard and seen eyes that seemed to glow looking back?
In what seems like another lifetime, I used to search for wolf spiders and other nocturnal animals at least once a week with 15 or so kids at a time as we ventured into the forest on night walks.
We kept the beam of our flashlights low searching the sides of the trails for small, but bright lights shining back at us.
Eyeshine is caused by light striking a special membrane behind the retina of the eye called the tapetum. It reflects the light back out of the eye to the light source, making it look like the eyes are glowing. Most animals with eyeshine are nocturnal hunters. By using the light twice, it allows them to see better at night.
Most wolf spiders (Lycosidae) hunt in the dimmer light of dusk and moonlight. Their four large posterior eyes have well-developed tapeta which help them spot prey movement in such low light conditions. At night, wolf spiders can be easily spotted because the tapeta in their large eyes shine brightly.
Other animals have eyeshine for the same purpose. Eyeshine can be different colors including pink, orange, yellow and green.