Understanding the Inner-workings of Carnivorous Mushrooms

In the 1980s, scientists discovered that oyster mushrooms are carnivores. The delicious, inescapable inference is that they’re the only vegan food that can itself eat meat.

The meat in question is definitely meat, too. Nematodes, also called roundworms, are little animals complete with guts, nerves, muscles and their own primitive form of hopes and dreams. Oyster mushrooms poison and paralyze nematodes within minutes of contact, inject their filaments into the corpses, dissolve the contents and absorb the slurry.

What was not known was how this fungal poison worked, or how extensive its powers were. A team of Taiwanese scientists that sought to answer those questions published their results last March in the Proceedings of the National Academy of Sciences. They discovered that the fungus targets a part of the worms so indispensable that nematode species separated by more than 280 million years of evolution were equally susceptible.

Before proceeding, however, it’s important to emphasize that oyster mushrooms are far, far from alone among fungi in their eating habits, probably because nematodes are the most abundant animals in soil. The little worms are so common that were the entire planet except nematodes dissolved, a dimly visible Earth-shaped shell of nematodes would be left floating in space. So, it is perhaps not surprising that this embarrassment of high-quality protein spurred an outburst of fungal evolution. Even so, the sheer devious ingenuity, diversity and abundance of the devices with which fungi responded to the challenge is grimly awe-inspiring. For example, a few species in a group of fungus-like organisms called oomycetes send nematode-sniffing hunter cells in pursuit of the worms, as do a few species of true fungi called chytrids (the same group that produced the pathogen that has decimated amphibians). They’re like something out of The Matrix, except in swimmy fungus form. Once their target is acquired, they “encyst” near the mouth or anus before injecting themselves into the worm and attacking its internal organs.

A second group of oomycetes in the genus Haptoglossa manufactures infective “harpoon cells.” These prey-seeking, pressurized nematode guns are programmed to glue themselves to a surface, barrel pointed upward. When a nematode blunders into it, a line of weakness snaps, deploying a harpoon that injects enough of the Haptoglossa spore to seal the worm’s demise. Although a similar apparatus is famously found in the stinging cells of jellyfish and coral, this appears to be a completely independent invention of pretty much the same equipment.

Some fungi produce booby-trapped bonbons. These spores have various irritating shapes like sickles, stilettos or—no kidding—chick-shaped marshmallow peeps, all of which seem calculated to lodge in nematode esophagi like fish bones in a diner’s throat. They must be tasty because nematodes swallow them anyway.