The poison effect harms pufferfish

It's a kind of animal🙂 Any natural living beings can be poisoned if the poison is enough toxic.

But spiders and cave spiders have poison immunity in minecraft.

Realistically, the spiders probably shouldn't be immune to poisons either... What's the first thing 90% of people reach for when they find a big, black, hairy spider in their loungeroom? A can of - you guessed it - poison. Additionally, the idea of spiders being immune to their venom is probably wrong. Spiders are certainly capable of killing other spiders, even in the same species.

As for the puffer fish - yep... They're actually immune to their own toxin. That's actually how they have it. It's not created in the fish itself, but by bacteria. But as far as spider venom or other poisons - they're going to die like any other animal.

Can confirm for 1.13-pre4.

I think spiders have immunity to poison has its reason. In Minecraft, they are unrealistically large and appear on the land when darkness comes; therefore they're more similar to some kind of mutated spiders. But pufferfish are natural.