Lichens are eaten by a surprisingly wide range of animals, from large Arctic mammals to tiny moth larvae. Despite producing hundreds of chemical compounds that deter many would-be grazers, lichens serve as a critical food source for caribou, certain primates, flying squirrels, snails, and specialized insects. Humans have eaten them too, for centuries.
Caribou and Reindeer
No animal is more closely associated with lichen consumption than the caribou. In northwest Alaska, lichens make up roughly 71% of caribou diets in late winter, with mosses and shrubs filling in the rest. Caribou dig through snow to reach ground-dwelling lichens, particularly species in the genus Cladonia, sometimes called “reindeer lichen” for exactly this reason.
Lichens are rich in carbohydrates but low in protein. Some lichen species contain polysaccharides that can account for up to 57% of their dry weight, making them a reliable energy source during harsh months when other forage is buried or dormant. Pregnant female caribou tend to eat slightly fewer lichens than males and non-pregnant females, likely supplementing their diet with higher-protein foods to support fetal development. Still, lichens remain the dominant food item across the herd for the entire winter season, and caribou populations are closely tied to the health of lichen-rich habitats.
Yunnan Snub-Nosed Monkeys
High in the mountains of southwestern China, the Yunnan snub-nosed monkey holds a unique distinction: it is the only higher primate whose primary food source is not a plant. These monkeys eat lichens year-round, with lichens comprising about 67% of all recorded feeding observations. They favor tree-hanging species like Usnea (old man’s beard) and Bryoria, pulling long strands from the branches of conifers and oaks in their high-altitude forest habitat.
This is an unusual dietary strategy for a primate. Most monkeys and apes rely on fruit, leaves, or insects. But at elevations above 3,000 meters, where fruit is scarce and winters are long, lichens provide a dependable food source that hangs from nearly every tree. The monkeys have adapted their foraging behavior around it, spending much of their day moving through the canopy harvesting lichen rather than searching for seasonal fruit.
Northern Flying Squirrels
In the conifer forests of western North America, the northern flying squirrel depends heavily on lichens during winter. Scat analysis from squirrels in central Idaho found that 86% of winter droppings contained algal cells from Bryoria, a hair-like lichen that drapes from tree branches. In summer, that figure dropped to 25%, as the squirrels shifted toward fungi, seeds, and other foods.
Flying squirrels also use Bryoria lichens as nesting material, weaving them into insulated dens inside tree cavities. This dual relationship, as both food and shelter, makes lichen-rich old-growth forests especially important habitat for these squirrels. In turn, flying squirrels are a key prey species for the northern spotted owl, so lichen health ripples through the food web.
Snails and Slugs
Gastropods are among the most common lichen grazers worldwide. At least nine snail species found on rocks and tree bark in European temperate forests regularly feed on lichens, and their grazing can significantly shape which lichen species thrive in a given area. Research has shown that lichen-feeding snails can limit the establishment and survival of young lichen colonies, effectively acting as a filter on lichen community composition.
But the relationship is more complicated than simple herbivory. When snails eat lichens, fragments of the lichen pass through their digestive systems and emerge viable in their droppings. Slugs can move at least 15 meters from a feeding site, carrying lichen fragments to new locations. This means gastropods may actually help lichens colonize new habitat through dispersal, even as they consume them. Rather than a purely destructive relationship, snail grazing appears to be a double-edged interaction that both limits and spreads lichen populations.
Lichen Tiger Moths
Among insects, the most dedicated lichen consumers are the larvae of lichen tiger moths, a group of roughly 4,000 species in the subfamily Lithosiini. Unlike other caterpillars that might nibble lichens occasionally, these larvae are obligate lichen feeders, meaning lichens are their required food source. They’ve evolved specialized mouthparts with a hardened grinding surface called a mola that lets them break through the tough outer layer of a lichen’s body.
These caterpillars don’t just eat lichens for calories. They absorb defensive chemicals from the lichens and store them in their own tissues, retaining these toxins through metamorphosis into adulthood. This chemical armor, borrowed directly from their food, helps protect them from predators at every life stage. Researchers believe this ability to feed on chemically defended lichens and then co-opt those defenses was the key innovation that allowed lichen tiger moths to diversify into thousands of species.
How Lichens Defend Themselves
Lichens are not passive food. They produce over 700 known secondary compounds, many of which serve to deter herbivores and prevent colonization by pathogens. Usnic acid, vulpinic acid, and stictic acid are among the most studied. These compounds can taste bitter, disrupt digestion, or be outright toxic. Vulpinic acid, found in wolf lichen, is poisonous enough that Indigenous peoples in parts of North America historically used it as a wolf poison.
These chemical defenses explain why relatively few animals eat lichens compared to leafy plants. The species that do consume lichens have generally evolved specific adaptations to tolerate or exploit the chemistry, whether that’s the caribou’s specialized gut microbiome, the moth larva’s toxin-sequestering tissues, or the snail’s ability to pass lichen fragments through its digestive tract intact.
Humans as Lichen Eaters
People have eaten lichens for centuries, though almost always with careful preparation. Wila, made from the lichen Bryoria fremontii, was an important food for Indigenous peoples in parts of North America, typically prepared through pit cooking, a slow process that breaks down tough polysaccharides and removes bitter compounds. Rock tripe, a group of leafy lichens in the genera Umbilicaria and Lasallia, has served as an emergency food across North America and remains part of traditional cuisine in Korea and Japan, where one species is used in various dishes.
In the Himalayas and southwestern China, several lichen species are prepared as vegetables through stewing, steaming, frying, or making soup. The common thread across cultures is that lichens are almost never eaten raw. Cooking processes are often complex and specifically designed to remove toxins, reflecting the same chemical defenses that deter animal herbivores. Without proper preparation, many edible lichens would cause nausea or digestive problems.