By Lorelle Sherman, OSU Extension Forester
It’s mushroom season! If you’re like me, you’ve been out in the woods searching for edible wild mushrooms at every free moment. While mushrooms can fruit year-round, fall is the undisputed season of fungal abundance. And we aren’t the only ones who notice. Many forest creatures take advantage of this seasonal bounty. Mushroom hunters often see telltale signs of wildlife nibbling, scratching, or taking generous bites out of mushrooms.
The consumption of fungi is called mycophagy, and animals that eat fungi are known as fungivores. Though mushrooms are mostly water (70–90%), they also contain proteins, amino acids, vitamins, and minerals. For some wildlife, fungi are a year-round dietary staple; for others, they’re a seasonal snack that provides essential nutrients when other foods are scarce or low in quality.
Let’s take a look at some of the wildlife that share our taste for mushrooms.
Rodents
Rodents are gnawing animals and have large, chisel-like incisors which often leave teeth marks on mushroom caps. They don’t usually consume an entire mushroom fruiting body, but will target the gills where protein-dense spores increase the caloric value. Structural parts of a mushroom, like the stipe, are mostly made of chitin and water which lacks the same nutrition. Chipmunks and squirrels (family Sciuridae) consume a remarkable variety of fungi. For some species, fungi make up over 70% of their yearly diet by volume.
In northern latitudes, squirrels even harvest and dry mushrooms for later use. I was elated to witness this in the Yukon Territories this past summer. After noticing one odd mushroom hanging in a tree, I started seeing dozens of mushrooms decorating trees like ornaments. Nature’s dehydrator! Once the mushrooms are dried out, the squirrels collect them for storage through the winter. Drying concentrates food value; fresh mushrooms contain only 0.1–0.7 kcal per gram, compared to 4–6 kcal per gram when dried. (Curious about truffle-loving rodents? Check out this blog post.)
Bears
Black bears are omnivorous and opportunistic, meaning they will eat whatever is available. Black bears in the Pacific Northwest are known to eat truffles (hypogeous) and mushrooms that fruit above ground (epigeous). In fact, I’ve seen clear signs of black bears chowing down on Matsutake (Tricholoma murrillianum) right along the coast. Historical accounts from coastal Washington describe bears as heavily feeding on fungi (Poelker and Hartwell 1973).
Grizzly Bears in the Rockies obtain most of their energy from the seeds of whitebark pine (Pinus albicaulis), or from bison or elk carrion. In years when whitebark pine seed availability is low, grizzly bears will consume more mushrooms to fill the protein deficit. With whitebark pine now listed as endangered, fungi may become an increasingly important food source for these bears.
Birds
While mammals get most of the attention, some birds are also mycophagists. Turkeys and grouse scratch through leaf litter in search of food and often encounter fungi. They are opportunistic feeders which will consume whatever they uncover. Studies have found truffles in wild turkey (Meleagris gallopavo) stomachs and identified 31 fungal taxa in the digestive tracts of spruce grouse (Falcipennis canadensis). As any mushroom hunter will know, there are many species of mushrooms that readily become infested with insect larvae. Crows and jays tear apart mushrooms to reach the insect larvae inside, while gray jays (Perisoreus canadensis) sometimes eat fungi and slime molds directly.
Birds secondarily consume fungi by eating fungus-loving insects. There are also raptors that love to eat mushroom-loving rodents. Birds are likely acting as indirect fungal spore dispersers by consuming other creatures that eat fungi.
Some birds that that nest in cavities in standing dead trees, like woodpeckers, rely on wood decay fungi to soften the wood enough to facilitate cavity excavation. In turn, spores from the wood decay fungi get trapped in their feathers and are dispersed to new trees as they fly around. This act of fungal spore dispersion facilitates future cavity excavation for themselves or other woodpeckers.
Slugs & Snails
Slugs are true mycophagists, fungivores, mushroom lovers. Their feeding damage is easily recognized by their mining habits which sometimes create holes through the cap. You can often see the remnants of slime trails on or around the mushroom. Sometimes slugs eat the mushroom entirely and all that’s left are slime trails. The Pacific Northwest’s banana slug (Ariolimax columbianus) especially favors boletes, oyster mushrooms, and Agaricus species. Slugs play an ecological role, too. They act as small-distance dispersers of truffle spores and actually stimulate mycorrhizal growth between truffles and tree roots when fungal spores germinate in their guts.
Slugs aren’t the only Mollusk that feed on mushrooms. Snails are less studied, but community science platforms like iNaturalist have revealed many records of snail mycophagy.
Turtles
Box turtles are opportunistic feeders and will feed on whatever is available and abundant, including mushrooms. Instead of teeth, turtles have beaks made out of keratin. The beak shape varies by species depending on their diet. Box turtles, like the one in the photo, have triangular beaks that leave a very distinctive triangular bite mark in the mushroom. A series of these bites can leave a crown-like pattern—an unmistakable sign of turtle dining.
Ungulates (Deer & Elk)
Deer and elk often encounter mushrooms while foraging, and in some regions and seasons they actively seek them out. Fruiting bodies of mycorrhizal fungi such as Russula, Lactarius, Amanita, and Boletus species have been documented in their diets. These fungi are rich in protein, minerals, and moisture, which can be especially beneficial during dry summer months when forage quality declines. Fungal consumption also supplies micronutrients such as phosphorus, potassium, and trace elements that may be limited in plant tissues. Fungi generally have higher protein by volume than plant tissue and are easier to digest, making them a high-quality food source for ungulates. One study noted that elk always consumed mushrooms when encountered and sometimes had a taste for leafy lichens as well.
Despite its ecological importance, fungal foraging by wildlife remains under-studied. Seasonal availability, habitat type, and individual preference all influence how much fungi contribute to diet. But diet study methods often miss fungal remnants because soft mushroom tissue readily breaks down in the gut. Fungal spores are often missed when researchers use sieves to sort diet contents that are too large and allow the spores to pass through. Researchers are now using techniques such as DNA metabarcoding of scat samples to improve understanding of the complex relationships between fungi, wildlife, and forest ecosystems.
Next time you’re out mushroom hunting, look closely… those nibbled edges, bite marks, or slime trails might tell you who got there first. Who ate your mushroom?
