A few weeks ago, we got 3.7 inches of rain in Fifield from a tropical storm originating in the Gulf of Mexico. This was only the fourth time a tropical storm hit Wisconsin since weather records began in 1851. We also had some warm and humid weather during that time conducive for growing mushrooms on horse dung.

A mushroom, sometimes called a toadstool, is the fleshy, spore-bearing fruiting body of a fungus typically produced above ground, on soil, or on its food source — in this case horse dung. After that rain event, hundreds of mushrooms spouted profusely within a short period of time on horse manure that had been leveled out over soil. This, along with the rain and warm weather, created perfect growing conditions for a specific type of mushroom called the egghead mottlegill. The rather sudden appearance of mushrooms at this time of year when most appear in late summer or fall, piqued my interest, so I decided to find out more about them.

Grazing herbivores like horses and cattle swallow thousands of mushroom spores. Some mushroom spores have a special coating on them that make them impervious to stomach enzymes that easily digest other spores. Once the dung is voided, digest-resistant spores germinate like seeds, grow, and produce more mushrooms that produce more spores. When those spores are eaten by herbivores the whole interesting process begins all over again.

Did you know that the traditional substrate for commercial mushroom cultivators is well-rotted horse manure, the organic matter that has already undergone its primary decomposition by passing through the digestive tract of a horse? Secondary decomposition by other fungi and insects occurs after the dung leaves the horse.

The egghead mottlegill is a buff, or whitish-colored, saprophytic mushroom that is widely distributed and is present in many temperate zones of the world. A saprophytic mushroom is one that lives on dead or decaying organic matter. It is native to North America and can appear at any time of year when the ground isn’t frozen. It is sticky when wet and wrinkled when dry. It grows quickly and disappears just as fast.

The egghead mottlegill mushroom gets its name from the mottling of its gills and looking like the top half of an eggshell. Perhaps a better descriptive name for it would have been, ‘half eggshell mottlegill’! The gills, located on the underside of the mushroom, are off-white to start with becoming mottled brown and darkening to black as the spores mature. Spore prints can help identify mushrooms by placing mushroom caps on white and black paper for a day or two.

A word of caution, the egghead mottlegill is regarded as inedible, so it is not for chewing and should be viewed only.

Nicholls can be reached at nicho002@umn.edu.