Illustration of a cross-section through a cave showing the three distinct zones. At the start of the cave is the entrance zone. This zone receives sunlight. Plants can grow in this zone and the temperature is variable. Animals, including racoons, use this area to nest, feed or rest. The next zone is the twilight zone. It receives very little light and has minor fluctuations in temperature. Insects, spiders and bats inhabit this zone. The deepest zone is the dark zone. It receives no light and has a constant temperature. Animals living in this zone are adapted to the dark conditions. Some will never leave the cave. These animals lack skin pigment and have no, or very poorly developed, eyes.