“Can you eat them?” is the question I’m inevitably asked when we find dense mats of mushrooms growing up from our wood mulch after a good rain.
And while these ones look quite showy and fleshy, you’d easily walk by them without a second glance. Each mushroom is no more than the size of a pinky nail, just a few millimeters wide and tall. In their immature state, the mushrooms are inconspicuous nubs with spiky sides, fully enclosed to protect the “eggs” inside. As they age, the caps break away to reveal a nest of eggs denotive of the mushrooms’ common name: bird’s nest fungi.
These are not the bird’s nest in Chinese bird’s nest soup (which are actual birds’ nests from the edible-nest swiftlet and black-nest swiftlet). Bird’s nest fungi are considered inedible due to their tiny size, though no study has ever shown them to be poisonous.
Harold J. Brodie, a Canadian mycologist who studied bird’s nest fungi extensively, concluded in his 1975 book, The Bird’s Nest Fungi, that the mushrooms were “not sufficiently large, fleshy, or odorous to be of interest to humans as food,” though some species have been used by native peoples to stimulate fertility. The 1910 publication Minnesota Plant Studies suggests they are “not edible owing to their leathery texture.”
Bird’s nest fungi are part of the Nidulariaceae family of fungi, known for their fruiting bodies that resemble egg-filled birds’ nests. The fungi that show up most frequently in my garden are Cyathus striatus, which have flared, tan-colored cups holding dark gray eggs.
The eggs are almost metallic looking, and up close they resemble shiny river stones. The periodoles, as the eggs are called, serve as protective sacs for the mushroom’s spores. When drops of water land in the cup, they eject the periodoles up to four feet away. At the scale of several millimeters, even a single raindrop can exert enough force to launch the periodoles like a water cannon. This method of dispersal is why you’ll sometimes hear the mushrooms referred to as “splash cups.”
This is where it gets really interesting: each periodole is connected to a funicular cord, essentially a long, fine thread with a sticky tail that unwinds several inches. As the periodole sails through the air, the cord may come in contact with, say, a twig or a blade of grass. It gets caught by its tail and rapidly wraps around the twig, much like a high-flying game of tetherball. Here it remains until the right conditions present themselves for the periodole to release the spores.
When they germinate, they grow into branching filaments called hyphae. The mass of hyphae (mycelium) weaves through moist woody debris and consumes the wood to fuel its growth. This process is largely how wood decomposes. When two different mating strains of mycelia fuse together, they form a new bird’s nest fungus.
Bird’s nest fungi spring up in dead tree trunks, rotted timber, wood mulch, bark chips, sawdust, or humus-rich soil, and you’ll often find them in animal dung as the periodoles can survive a journey through the digestive tracts of cows and horses.
They’re a fairly common sight in damp, woodsy environments in temperate climates. And though they don’t catch your eye right away or make for good eatin’, the biology of these tiny shrooms is truly fascinating.