Are mushrooms kosher?

Why it's not that simple

A mushroom is neither a plant nor an animal, which puts it in an odd halachic position:

• There is no species question at all. The signs that decide whether an animal is kosher have nothing to work on here, and no fungus appears anywhere in the Torah’s lists. A mushroom is inherently permitted.
• It is a genuine halachic curiosity: a fungus does not count as ground-grown for the purposes of its bracha, which is why the bracha on mushrooms is shehakol rather than borei pri ha’adamah.
• For insects, though, it is treated exactly like any other produce. The worms that grow in mushrooms and truffles are forbidden despite that bracha status — the mushroom counts as attached to the ground, and the prohibition on “the creeping thing that creeps on the earth” reaches it. How produce is checked →
• Mushrooms grown on wood or on a prepared medium rather than in soil still need checking. What they are growing on does not exempt them.
• Cultivated is not the same as clean. Rav Moshe Feinstein addresses exactly the modern case — mushrooms grown under conditions, including spraying, meant to keep insects out — and holds that checking is still required l’chatchila. An industrial growing process is a reason to expect a clean mushroom, not a reason to skip looking.
• Where mushrooms actually need a hechsher is once they stop being mushrooms: canned, dried, powdered, in a stock or an extract. There the question is the brine, the carrier, the processing aids and the equipment — not the fungus.