I grow shiitake mushrooms on oak logs in my basement. Last week, I noticed two small mushrooms budding on one of them. The next day, one was larger but the other was gone. A couple of days later, I noticed that the cap of the mushroom seemed to be deformed or missing on one side. The next day, more was gone, and finally, there was just the stalk. I wondered if mice were eating my mushrooms, but our two cats have access to the basement all day and night, so I doubted if it were mice.
The next day, when I went to water them, I noticed something strange on the stalk; it was a slug who was eating the stalk. That slug must have eaten the cap a little at a time each day. I'll put some slug bait under the shelves, out of reach of the cats of course, and hope that solves the problem.
Paul