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ST. JOSEPH, MO (CNN) -- Some mushroom hunters in Saint Joseph, Missouri say they're making some really big finds.

They're called giant puffballs. Usually, they're the size of a grapefruit. but a retired Missouri Western State University professor and another man in St. Joseph have found several much larger than that recently.

Professor Richard Crumley says they are edible when they're young, but you have to do your homework. He says, "Well these are not. Now there are some puffballs that you wouldn't want to eat, they kind of look like this, but if you cut it them open and they have purple in the inside, you don't want to eat those. They're nasty."

Crumley says they're very common in Missouri and throughout the Midwest. He planned on taking home the big one he found on Wednesday, cutting it open, and eating it.