Ferns are an ancient and diverse group of plants that have existed on Earth for over 300 million years. They thrive in a variety of climates, from humid tropical rainforests to cooler, more temperate regions. These non-flowering plants do not reproduce with seeds but instead use spores.
Animals That Consume Ferns
Many animals incorporate ferns into their diets, though often not as a primary food source. Large herbivores like deer, elk, and moose will browse on fern fronds, especially when other more preferred vegetation is scarce, such as during winter months or in areas with high animal populations. White-tailed deer, for example, may eat ferns when other vegetation is scarce. Elk graze on ferns in forested areas, and specific types like western sword fern are important food sources for Roosevelt elk and black-tailed deer. Moose also consume several fern species, including royal fern, though ferns typically constitute an insignificant portion of their overall diet.
Smaller mammals, such as rabbits, voles, mice, and squirrels, may also consume ferns. The mountain beaver, a rodent found in the Pacific Northwest, is a notable fern consumer, with over 75% of its diet consisting of ferns like bracken and sword fern. Mice and voles might eat the rhizomes or lower portions of ferns, especially if other food sources are limited.
Insects also interact with ferns as a food source, though fewer insect species specialize on ferns compared to flowering plants. Caterpillars, including specific types like the Florida fern caterpillar, feed on young fern fronds. Sawflies and certain true bugs, such as aphids, are more commonly found feeding on ferns, often by sucking plant juices rather than chewing tissues. Slugs and snails are also known to consume fern foliage.
Considerations for Fern Consumption
While a variety of animals consume ferns, the edibility and safety of these plants vary significantly by species and the amount consumed. Some ferns contain compounds that can be toxic to animals, particularly in large quantities or over extended periods. Bracken fern (Pteridium aquilinum) is one of the most widely distributed and notorious toxic ferns. It contains ptaquiloside, a carcinogenic compound, and thiaminase, which can lead to vitamin B1 deficiency in affected animals.
Livestock such as cattle, horses, and sheep can be poisoned by bracken fern, with symptoms ranging from blood disorders and blindness to cancerous tumors in the urinary bladder. The toxic effects are cumulative, meaning prolonged consumption of even small amounts can be harmful. Animals often instinctively avoid toxic plants if other food is available, but they may consume them when forage is scarce, such as during droughts or in overgrazed pastures.
The “fiddleheads,” or young, coiled fronds of some ferns, are consumed by certain animals, and by humans after specific preparation. However, the most toxic parts of ferns, including bracken fern, are often the rhizomes (underground stems), followed by the fiddleheads and young leaves. Cooking and preparation can reduce the toxicity of some ferns, but it may not eliminate all harmful compounds.