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Nature Notebook – Tapetum

On a recent night hike the scouts and I slowly moved our flashlight beams across the creek. Then we saw them…tiny sparkles visible only when light passed over the area. We had found spider eye shine!

The sparkles appear when a light beam reflects off a specialized structure present in most nocturnal animal eyes. The tapetum is a thin layer of cells that acts like a mirror. Any “stray” light beams that miss the photoreceptors located on the retina, run into the tapetum and reflected back to the photoreceptors for a second chance of absorption. This allows nocturnal animals to maximize whatever light is available to them at night.

The reflective surface of the tapetum is also responsible for the creepy glowing eyes of night animals. The colors are influenced by the presence of substances such as riboflavin or zinc in the tapetum as well as retinal pigments and even age of the animal.