Low-altitude pikas survive by eating moss, but very few other animals can do so because moss is a very poor-quality food, says National Geographic. Fairfax County Public Schools reports that a few small mites and crustaceans eat moss, but most small animals use it as shelter material rather than food.
Fairfax County Public Schools reports that moss is very important in the ecosystem, although not as a food source. According to National Geographic, moss is a poor-quality food because it is 80 percent indigestible fiber and does not provide sufficient nutrients. Most mammals cannot survive by eating moss exclusively, although many occasionally nibble at it. Pikas use a tactic called copraphagia to extract maximal nutrition from moss: they eat their own feces and re-digest it.
Caribou and reindeer feed primarily on a plant called caribou moss during mid-winter. However, according to Blue Planet Biomes, caribou moss isn't technically a moss; it's actually a lichen. A true moss, called Arctic moss, is eaten by some migrating birds.
Fairfax County Public Schools reports that many small animals rely on moss as a shelter material, and during droughts they may access it as a source of water. Many birds line their nests with mosses.