I found several (I thought) of these beetle larvae inside the stems of an annual patch of vivid orange mushrooms that arise from a ground-level stump. I placed several mushrooms in a open leftover container with 10 - 15 mm or soil on the bottom, figuring the larvae would leave the fungi and pupate in the soil once the rotting/fermentation reached a certain point.

(Bitter experience has taught me that placing mushrooms in a closed or even narrow-mouthed container quickly kills any critters living in them. Decomposing mushrooms apparently give off a great deal of carbon dioxide and maybe other gases.)