Fungi are eaten by an enormous range of organisms, from microscopic worms in the soil to large mammals and, of course, humans. Flies and beetles alone account for the most species-rich groups of fungal feeders, but the list extends to slugs, snails, squirrels, deer, primates, nematodes, and even other fungi. Understanding what eats fungi reveals how central they are to food webs in nearly every ecosystem on Earth.
Insects: The Largest Group of Fungal Feeders
Among all animals that eat fungi, insects contain the greatest number of species that do so. Flies (Diptera) and beetles (Coleoptera) are the two most species-rich groups. Some are obligate fungivores, meaning fungi are their sole food source, while others eat fungi alongside decaying wood or other organic material. Many wood-dwelling beetles depend on fungi that break down lignin and cellulose in dead trees, feeding on the fungal tissue that colonizes the wood rather than the wood itself.
The diversity of fungus-eating beetles is striking. Some of the smallest beetles in the world, including the feather-winged beetles (Ptiliidae), feed on fungi. Rove beetles (Staphylinidae), one of the largest and least-studied beetle families, include both predatory species and specialized fungivores that live in moist mushroom habitats. Adults of round fungus beetles (Leiodidae) eat fungal spores, while their larvae feed on slime molds. Decaying mushrooms also attract carrion beetles, water scavenger beetles, and scarabs. Even the masses of spores produced on the surface of rotting plant material host their own specialist beetle communities.
Leafcutter Ants Farm Their Own Fungi
One of the most remarkable relationships between insects and fungi involves leafcutter ants, which don’t just eat fungi but actively cultivate them. These ants harvest fresh plant material and carry it back to underground gardens where they use it as a growing medium for a specific fungal species. The fungus breaks down the plant matter into nutrients the ants can’t access on their own, then produces nutrient-rich swellings called gongylidia on its branching filaments. These swellings are packed with fats, carbohydrates, and other nutrients and serve as the primary food source for the entire colony. Developing larvae and brood eat nothing else.
The most studied of these cultivated fungi is a species called Leucoagaricus gongylophorus, grown exclusively by the most advanced lineage of fungus-farming ants. This is a true agricultural partnership: the ants provide the fungus with a substrate it couldn’t colonize alone, and the fungus converts plant biomass into a concentrated food the ants can digest.
Slugs and Snails as Fungal Grazers
Slugs and snails are widespread consumers of mushrooms and other fungal fruiting bodies. Genera such as Arion, Limax, Ariolimax, and Meghimatium have all been documented feeding on a variety of fungal species. But their role goes beyond simple consumption. Slugs also serve as spore dispersers: fungal spores pass through their digestive tracts and are deposited in new locations through fecal matter.
Research on the slug Meghimatium fruhstorferi found that spores of several mushroom genera actually had higher germination rates after passing through a slug’s gut compared to spores that were never consumed. Field tracking showed individual slugs traveling over 10 meters in five hours across forest floors, litter layers, and tree trunks, potentially carrying spores of wood-decaying, soil-dwelling, and root-associated fungi to new sites where those fungi can establish colonies. This means slugs don’t just eat fungi. They help them reproduce.
Mammals That Depend on Fungi
Many mammals eat fungi, but few depend on them as heavily as the northern flying squirrel. In studies from the Black Hills of South Dakota, underground truffles appeared in over 98% of flying squirrel scat samples during peak summer months, with fungi composing up to 99% of the material found. Plant and animal components didn’t come close. This makes the northern flying squirrel one of the most fungus-dependent mammals documented.
Eurasian red squirrels can meet up to half their daily energy needs from fungi alone. North American red squirrels regularly eat mushroom gills. White-tailed deer are among the most prolific mammalian fungivores, reported to eat as many as 580 fungal species. Deer in the family Cervidae as a whole rely heavily on fungi as a significant portion of their diet. Among primates, Japanese macaques eat at least 67 fungal species, and langurs in Southeast Asia have been observed eating mushrooms as well. For many small forest mammals, fungi represent a critical source of calories and nutrition that bridges gaps between other seasonal food sources.
Microscopic Fungivores in the Soil
Below the forest floor, an invisible army of organisms feeds on fungi. Soil nematodes, tiny roundworms typically less than a millimeter long, include species specialized for piercing and consuming fungal filaments. These fungal-feeding nematodes have mouthparts completely different from those that eat bacteria or plants, with stylets designed to puncture fungal cell walls and extract the contents. Their feeding helps regulate fungal populations in soil and influences the balance between fungi and bacteria in the microbial community.
The composition of nematode communities in soil can actually indicate how healthy or disturbed an ecosystem is. Fields dominated by short-lived, fast-reproducing nematode species tend to have higher levels of soil-borne fungal pathogens, while those with longer-lived, more specialized species signal a more stable and balanced soil food web.
Fungi That Eat Other Fungi
Some of the most effective fungal predators are other fungi. This process, called mycoparasitism, involves one fungus attacking and consuming another. The attacking fungus uses two main strategies: it secretes enzymes that dissolve the host’s cell walls, and it produces toxic secondary metabolites that kill host cells from the inside. Key enzymes include chitinase and glucanase, which break down chitin and glucan, the structural components that give fungal cell walls their rigidity. Once the cell wall is breached, the contents leak out and the parasitic fungus absorbs the nutrients.
Species in the genus Trichoderma are among the best-known mycoparasites and are widely used in agriculture as biological pest control agents. Other mycoparasitic fungi include Aureobasidium pullulans and Ampelomyces quisqualis, which specifically targets powdery mildew. Microscopic examination of one such interaction showed the parasitic fungus wrapping its filaments around the host’s spores, disrupting cell walls and causing the internal contents to leak out. This is not passive competition. It is active predation, fungus consuming fungus.
Humans and the Global Appetite for Fungi
Humans are, collectively, among the most significant consumers of fungi on the planet. Cultivated species like button mushrooms, shiitake, and oyster mushrooms form the bulk of commercial production, but wild-harvested species carry enormous cultural and economic importance. Porcini (Boletus edulis), chanterelles, and truffles (Tuber species) are prized in cuisines worldwide. Chanterelles are particularly marketable because they have a longer viable period after harvest than many other wild species. Porcini’s flavor actually intensifies when dried.
In Asia, demand for medicinal fungi like reishi (Ganoderma) and cordyceps (Cordyceps sinensis) has long driven a significant commercial market. The nutritional profile of edible fungi varies by species but generally includes protein, dietary fiber, B vitamins, and minerals. Despite their widespread use, the full nutritional range of wild edible fungi has not been thoroughly analyzed, and relatively little is known about how nutrient content varies within a single species growing in different regions.
How Fungi Fight Back
Fungi are not passive targets. Like plants, their primary defense strategy is chemical. Fungi produce a range of toxins, including secondary metabolites, specialized peptides, and defensive proteins that target the biology of whatever is trying to eat them. The strategy differs depending on the threat. Compounds aimed at competing bacteria or fungi are typically secreted outward into the surrounding environment. Toxins aimed at animals, by contrast, are stored inside fungal cells and only released when the tissue is consumed.
The death cap mushroom and its relatives in the genera Amanita, Galerina, Conocybe, and Lepiota produce alpha-amanitin, a potent toxin that enters the digestive tract lining upon consumption and shuts down a critical enzyme needed for gene expression in animal cells. The mold Aspergillus nidulans takes a subtler approach, producing compounds that mimic insect hormones and disrupt normal development. The ink cap mushroom Coprinopsis cinerea produces enzymes that degrade the chemical signals bacteria use to coordinate group behavior, effectively silencing bacterial communication. These defenses haven’t stopped the long list of organisms that eat fungi, but they’ve shaped which species can do so safely and which cannot.
Why Eating Fungi Matters for Ecosystems
Fungivores do more than just consume. They reshape how nutrients move through ecosystems. Fungi are the primary drivers of nutrient cycling in soil, breaking down organic matter and making nitrogen and phosphorus available to plants. When animals eat fungi and deposit spores in new locations, they help fungi colonize fresh territory and maintain the networks of root-associated fungi that most trees and plants depend on for nutrient uptake. Flying squirrels eating underground truffles and depositing spores across the forest floor are performing an ecological service the trees themselves rely on.
In grassland and forest soils, fungal communities directly influence the abundance of genes involved in nitrogen mineralization and phosphorus cycling. As ecosystems recover from disturbance, fungal communities reassemble in ways that increase carbon storage and nutrient availability. The organisms that eat, disperse, and regulate those fungal communities are integral to the process. Every slug trailing spores across a log, every beetle burrowing through a mushroom cap, and every squirrel caching a truffle is participating in a nutrient cycle that sustains the broader ecosystem.