The more we learn about nature, the more distressingly clear it is that nature doesn’t pay that much attention to the stuff we’ve spent decades writing about it. Recently it was established that animals play for sheer enjoyment – it’s not an evolutionary ruse to get them to practice real life, as we asserted for hundreds of years. Real life includes jubilant fun for the majority of animal species.
We once held up “mate for life” critters like penguins and swans as exemplars of marital fidelity, only to later realize that while couples do stay together, you can bet the farm that in nesting season, both partners are slutting around like James Bond on ecstasy. And whitetail deer jumped out of the “herbivore” box we assigned them, caught on video with mouths full of carrion, or pulverizing mice to death for a snack. Despite lacking decent equipment to kill and consume prey, hippos, giraffes, and other “strict herbivores,” as we had described them, routinely break their vows of vegetarianism.
Fungi, whose job it is to decompose organic matter, also flunked biology class, because many common species hunt or trap live prey and then eat them. If I was vegan, I’d worry that chicken-of-the-woods (Laetiporus sulphureus), which has a texture and flavor similar to that of chicken, or beefsteak shelf fungi (Fistulina hepatica), with the look and feel of raw beef, might be gateway foods back to meatland. What would really blow my mind, though, would be deciding whether it was OK to eat mushrooms that thoughtlessly kill and consume animals.
I suppose it’s generous to call minute roundworms with rudimentary nervous systems “animals,” but technically they are. Actually, four of every five animals on Earth are nematodes. Without exaggeration, they live all over –– in soil, water, plants, animals, and elsewhere. Microscopic for the most part, their ecological roles are legion: beneficial, pathogen, parasite, and detritus eater, to name but a few nematode careers. As USDA researcher Nathan Cobb wrote in 1915, “If all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes.” Yikes. Maybe it’s alright if fungi take a few nematodes out of the picture.
Fungi have invented truly devious methods to kill nematodes. They scatter pressurized spore-harpoon capsules that spear a nematode and inject it with fungal spores when it blunders into one of these minefields. Snares are popular with many species, filament hoops that instantly inflate to garrote nematodes out for a casual slither. Sticky traps are also common, and a few species deploy flagellated, nematode-seeking “hunter cells” that aim for a nematode’s mouth or butt to get fungal spores inside. And of course there are poisons. Almost seems like fungi took a few pages from Agatha Christie where nematode murder is concerned.
Fungal-based nematode toxins are of special interest to agronomists, as a small but significant number of nematodes damage soybeans, rice, and other critical crops, as well as trees. The newly discovered and worrisome beech-leaf disease is caused by nematodes. A major problem is that pathogenic nematodes are becoming resistant to the chemicals meant to control them. This is where fungi might help provide new options.
Native and widespread, the oyster mushroom (Pleurotus ostreatus) can be wild-harvested, and is one of the easiest mushrooms to cultivate because it will grow on toilet paper, sawdust or any kind of wood product. As its name implies, it is roughly shellfish-shaped, and cream-colored. I think it tastes quite good, though it doesn’t have the status or mystique of a shiitake or winecap mushroom.
I’m guessing (and hoping) there aren’t nematodes in toilet paper, but oyster mushrooms in the forest get to meet nematodes all throughout a rotted tree. When they encounter an oyster mushroom hypha (thread) in a decayed stump, the fungus exudes a toxin to paralyze nearby nematodes. Maybe it’s their version of fishing with rotenone, a natural compound that immobilizes fish. Then the worms are invaded by hyphae, their innards slurped up like in some creepy sci-fi film.
Apparently this chemical affects calcium-ion channels, which is the mechanism by which some blood-pressure drugs and anesthetics work. Calcium ion flow is carefully managed in muscle cells, kind of pumped around to various cellular processes depending on what the muscle is being asked to do. In this case, the nematodes’ muscle movement is short-circuited and the little worms turn to mushroom food.
Research has found that this oyster-mushroom toxin is distinct from any known commercial nematicides. Hopefully the world will soon benefit from new fungal-based control methods for nematode plant pathogens. I also hope we will continue to eat mushrooms even if those delectable fungi are partly made of worms.
Paul Hetzler is an arborist and former Cornell Cooperative Extension educator. He likes mushrooms, worm-fed or otherwise.
Oyster mushroom photo courtesy of Cornell Cooperative Extension/Almanack archive