I don't think it matters in most contexts. When people are casually talking about it, venomous and poisonous are both stand-ins for "it has venom." They're not telling other people, "actually, don't eat spiders." I was just joking about the classic pedant line about spiders.

But it does make a difference on paper. I'm curious how you would express this in German: A black widow is venomous and in theory a healthy human can eat a dead black widow with no ill effects.