In the county of Essex in England there is a rhyme:
the moon is at the full
Mushrooms you may freely pull.
But when the moon is on the wane
Wait ere you think to pluck again.
Quite mistakenly it implies that the moon influences fungal toxicity! But here is another explanation of why some fungi are poisonous:
A Bohemian folk tale tells of Jesus and Peter sharing some alms as they walked through a forest. As they ate, a few crumbs of bread fell to the forest floor. The crumbs of brown bread became poisonous mushrooms, while those of white bread became edible ones.