I’ve often come upon mushrooms in the wild that appear to have been chewed by some fungivore (a species that consumes fungi). Yet, the only critters I’ve been able to find actively feeding on fungi have been slugs — terrestrial gastropods that are common here in the mountains of Virginia.
This spring was too dry for many fungi to bloom, with only a few ubiquitous species showing up here on Briar Ridge or at my former digs in Old Hollow, which is much damper. Then late-summer rains hit, and kept coming through early autumn, and several species of fungus perked up and bloomed — producing mushrooms, their reproductive organs. I found some had semicircle-shaped bites taken out of the edge of their caps, which indicated to me that slugs had likely dined on them, although none of the culprits were present.
With their anatomy, slugs aren’t exactly speedy diners. These gastropods often glue themselves to a mushroom cap with its slime, then munch away at the edge in an arc, leaving what looks like a single bite of a larger animal.
In the woods near the cabin where I’m staying, I found a group of more than a dozen mushrooms that I later identified as Bicolor Boletes (Boletus bicolor). They had chunks gnawed out of them not just along the edges but all over the caps. Some of the caps had been totally consumed, with just a bit of stalk left. Could slugs have done this? Are there other fungivores competing for these colorful ’shrooms?
While I’ve often seen slugs eating mushrooms, they don’t like dry, sunny weather, which was the case when I found this bolete group. I decided to come back in the evening, when it would be cooler and damper.
Near dark, I grabbed my cameras and headed for the boletes. Sure enough, one of the larger ones was covered with slugs, stripping the spongy caps from the mushrooms’ stalks. By the next morning, most of the boletes were significantly damaged. Within a few hours, all that was left of them were a few stalks, some chewed to the ground.
Still curious about what else eats mushrooms besides slugs (and we humans), I did more research. Turns out many species across the globe engage in fungivory (also known as mycophagy). Among them are mammals (including 22 primates), birds, insects, amoebas, gastropods, nematodes, bacteria, and plants as well as other fungi. While I’ve found a bug or two crawling on mushrooms from time to time, none appeared to be eating them.
Taking a break from my research, I serendipitously watched a nature documentary featuring Boreal Woodland Caribou (Rangifer tarandus caribou) in Canada. In the process of following and photographing this rare subspecies, the filmmakers discovered its fondness for mushrooms, which apparently had not been documented before. All caribou are predominantly herbivorous—eating grasses, sedges, leaves and mosses—but the boreal subspecies prefers ’shrooms when they can find them.
While I’ve forgotten the name of the show I was watching, I found another video, on the Wildlife Society website, of boreal woodland caribou foraging for mushrooms. This shouldn’t be too much of a surprise. Many cold-climate herbivores, including these caribou, eat a lot of lichen, which is a mutualistic combination of algae or cyanobacteria that live among filaments of some fungus species. But, as the filmmakers show, these caribou will pass by lichen to get to fungi when they are available.
While slugs seem to be the prominent animal fungivore, I have also encountered some odd-looking fungi that turned out to be hyphomycetes, a fungal form that doesn't have fruiting bodies (mushrooms)—consuming one that does.
As I was working on this column, I finally spotted one more possible fungivore — a woodlouse — when I was going through my photos. Woodlice are terrestrial crustaceans that eat dead organic matter on the ground, including fungi, although this particular woodlouse appeared to just be traveling across the underside of a polypore’s cap.
Despite slugs being a prominent fungivore, little has been written about their association with fungi, as two Canadian scientists studying the literature on this wrote in a 2010 article in the journal Fungi: “Indeed, most literature addressing the subject of slug-mushroom interaction is decidedly uninformative…, noting merely that certain slugs eat ‘fungi.’”