Parasite ecologists spend copious time studying parasitic fungi. For instance, we’re interested in controlling the fungal pathogens responsible for the wildlife diseases that have decimated populations of amphibians, bats, and snakes. And we’re fascinated by the Cordyceps fungi that manipulate the behavior of ants and other insects. But how often do we study parasites that infect fungi (i.e., host = fungus)? Before I tackle this question, here’s a little backstory:
Last week, I went grocery shopping and bought some baby portabella mushrooms. I was feeling lazy, so I bought them pre-sliced and packaged in a cardboard box, which had an open top and was clearly labelled “sliced baby portabella mushrooms”. When I was checking out, the adult human bagging my groceries picked up the box and asked, “Are these vegetables?”
Yes, a piece of my soul died. But the educator inside me immediately announced, without distress or pause, “Oh, no, they aren’t. We generally eat three types of organisms: (1) Animals, where meat comes from, (2) plants, where vegetables come from, and (3) fungi, where mushrooms come from.” And while the woman nodded, seeming to confirm this information from some previous memory, a different, dark voice in my head added, “…and they all have worms.”
Fortunately, some intelligent internal filter kept me from saying the last bit out loud. But as I made my way to my car, I became increasingly concerned that even though I could tell you what kinds of parasites infect most plant and animal host taxa, and I knew that fungi must have parasites, I didn’t know which parasites infected fungi.
I did some googling as soon as I arrived home, and I learned that fungi have fungal, bacterial, and nematode parasites. Larval flies in mushroom gills can also be considered parasites of fungi. But overall, I didn’t find much information about parasites of fungi in my (admittedly not exhaustive) search. It might be that (1) I gave up too soon, (2) we don’t use classical parasitological terms for parasites of fungi, and/or (3) we study parasites of fungi less than those of animals and plants.
If you’re an expert on the parasites of fungi, please share your wisdom with us!
Parasite Ecology 
I am far from an expert of parasites of fungi, but here’s a few I really like.
Entoloma abortivum is a hyperparasite of Armillaria mellea, a species of mushroom that causes white rot in woody plants. Along with being a very cool parasite, one of its claims to fame is that one of the largest living organisms is an individual fungus in the same genus covering around 9 square miles in Oregon (individuals of A. mellea can also reach massive sizes). E. abortivum attacks A. mellea, causing it to abort its fruiting bodies and produce odd, lumpy, white, sterile structures instead. For a very long time it was thought that A. mellea was attacking E. abortivum, since Armillaria was already known to be a parasitic genus and Entoloma was not thought to be, but that does not appear to be the case. See more here–http://www.mushroomexpert.com/entoloma_abortivum.html–in particular in the paper at the end.
Boletus (or sometimes Pseudoboletus) parasiticus attacks Scleroderma citrinum, a mycorrhizal puffball fungus. It is found as boletes–stalked mushrooms with pores–popping out of a deflated puffball.
Hypomyces lactifluorum is a fungus that attacks russulaceous mushrooms, appearing as an orange crust of sorts on their surface. It is known as the “lobster mushroom” among mushroom collectors, despite not being a mushroom, because it makes the mushrooms it parasitizes take on a rust red color. It makes several mushroom species more desirable for eating.
Tremella fuciformis attacks wood decay fungi, and spends part of its life cycle in yeast form until it encounters its preferred host, at which point it switches to a hyphal growth form and produces fruiting bodies. It is important in Chinese cuisine.
There are oodles more, and some can be found on this page: http://mushroomexpert.com/mycotrophs.html
Thanks for posting about fungal mycotrophs–they get so little attention, and they’re so cool.
Wow, thanks for sharing!
Was researching the very question and came across this as well: https://www.popsci.com/parasitic-plant-fungi-new-species/