Mosses are small, non-vascular plants that form dense green clumps or mats in damp, shady environments. Unlike most plants, they do not have true roots, stems, or leaves, instead absorbing water and nutrients directly through their simple leaf-like structures. While moss is not a primary food source for many animals, some species do consume it, highlighting its role in various ecosystems. This consumption can be a matter of survival, especially in harsh conditions where other vegetation is scarce.
Animals That Consume Moss
A variety of animals, from tiny invertebrates to large mammals, incorporate moss into their diets. Invertebrates such as slugs and snails graze on moss, using specialized feeding organs like a radula to scrape off bits. Certain insects, including some beetle larvae and springtails, also feed on moss, breaking down the plant material for nutrients. Peloridiids, often called moss bugs, are flightless insects found in the Southern Hemisphere that exclusively feed on mosses and liverworts.
Among vertebrates, several mammals rely on moss, particularly in challenging environments. Reindeer and caribou in Arctic and subarctic regions consume moss, especially in winter when other forage is scarce, serving as an alternative to their preferred lichens. Musk oxen in the Canadian Arctic, Alaska, and Siberia also include moss in their winter diet, particularly where lichens are sparse. Arctic lemmings commonly eat moss, as it remains available under snow in harsh conditions. The American pika, a small mountain mammal, can have moss account for up to 60% of its diet, thriving in cold, high-elevation habitats.
Some bird species also consume moss, though it is less common than for mammals. Barnacle geese, for instance, feed heavily on mosses during winter months, especially when other food sources are limited. Other geese species, such as snow geese and pink-footed geese, have been observed feeding on mosses during their breeding season in Arctic and subarctic regions. The Red Grouse is also known to consume moss capsules. While direct consumption is less frequent, some birds might incidentally ingest moss while foraging for insects or other small organisms living within moss beds.
Amphibians and reptiles do not consume moss as a primary food source. However, some small frogs and certain reptiles may ingest small amounts of moss incidentally while hunting prey within moss-rich habitats. Moss beds also provide moisture and shelter for these animals.
Why Moss is Eaten and Its Nutritional Role
Animals consume moss for various reasons, often when other, more nutritious food sources are unavailable. This is particularly true in harsh environments like the Arctic tundra, where moss can be one of the few plants accessible during winter. In these conditions, moss serves as an important survival food, even if its nutritional content is low. For instance, a reindeer would need to consume about 7 kilograms of moss to obtain the same energy from half a kilogram of tundra grass.
Moss has a low caloric and protein content and is high in fiber, making it challenging to digest. Despite these limitations, it can offer certain benefits. Moss has a high water content, which can serve as a source of hydration for animals in dry conditions. Some moss species, particularly those in Arctic regions, contain high levels of arachidonic acid. This compound is important for maintaining cell function at low temperatures, effectively providing a natural antifreeze compound that helps animals like barnacle geese and reindeer cope with extreme cold.
For animals that consume moss regularly, like pikas, specialized digestive adaptations are often present. Pikas, for example, can re-ingest their feces to allow gut microbes to further break down the fibrous moss, enhancing nutrient extraction. This process can make the consumed moss up to six times more nutritious for them. While mosses contain various secondary metabolites, some of which may have biological activity, these compounds are not cited as a primary reason for consumption.