Nobody would say „trujący wąż” (poisonous snake) or „jadowity grzyb” (venomous mushroom). The distinction is similar to English. There are exceptions and contexts where it can be used interchangeably but arguably the same is true for English.
Italy, the core remnant of the Roman Empire, has unmatched language diversity, often varies even from town to town. It's a colorful mosaic of micro cultures and customs where people from one region using different words for venom/poison is completely normal, in their local dialect. Everyone speaks standard Italian though.
You've never visited Italy ? They're not that far away and I'm sure you'll love it.
