Dear Hannah and Maddie,

April showers may bring May flowers, but as you have noticed, rain at almost any time of the year can bring mushrooms! And not just in the yard either, though they are easy to spot out in the grass. If you ever go walking in the woods after a good rain, you will see an amazing variety of sizes, shapes and colors of mushrooms. Mushrooms are an important part of the ecosystem, breaking down dead plant matter and making the nutrients available for new plants to use.

Although it looks like mushrooms appear out of nowhere, they really don't. A mushroom is only a small part of a large fungus, an organism that mostly lives underground. Even when there is no mushroom visible above ground, the fungus is living and growing in the soil of the yard. In fact, some fungi are believed to be among the biggest living organisms on Earth. There was a lot of publicity in 1992 when researchers found a fungus in Michigan that covered more than 30 acres. Since then, other examples of "humungous fungus" have been found, with some estimated to cover more than three square miles!

You can imagine an underground mushroom fungus as a vast web of very tiny threads weaving through the soil, breaking down organic matter in the soil for its food. If you dig through the soil, you may not see the fungus at all, since the threads are microscopic, or virtually invisible without the aid of a microscope. A mushroom grows when the fungus threads begin to grow together and form a large structure that sticks up out of the ground. This happens a lot after it rains because the fungus threads are delicate and very prone to drying out. A lot of moisture is needed to produce a mushroom, and so they tend to form only when the soil is very wet, like just after it rains. Temperature also plays a role in regulating mushroom formation.

Why does the fungus make a mushroom? It's how it reproduces. Just like a plant makes flowers and seeds, a fungus makes mushrooms and spores. Spores are the "seeds" of a fungus. If you turn a mushroom over, you can usually see what are called "gills" on the underside of the cap (the part on the top that spreads out). These are membranes that look a lot like fish gills. Each gill is lined with cells that make spores. They fall out of the bottom of the cap of the mushroom and are picked up by the wind so they can spread to other places far away. Spores can travel very far and high. Living fungus spores can be found at altitudes above 10,000 feet and thousands of miles away from land over the ocean.

It is very important that you NEVER eat any mushroom you find growing in your lawn, or any other wild mushroom, unless you know exactly what you are doing. Every year, people die from eating poisonous wild mushrooms they mistakenly thought were edible. It takes years of practice and teaching from an expert teacher to be able to tell edible wild mushrooms from poisonous ones. Stick to your store-bought mushrooms, which are grown specifically for eating by mushroom farmers, when you feel like eating a fungus.

Thanks for your question,
Aubie and Dr. Han