Short version: When did people start the nitpickery?
It seems that for most of the 900 or so years of the history of these two words they could be used interchangeably with regard to animals that injected a toxic substance, the main idea, as I understand it, that venom is a subset of poison.
But at some point, someone decided that it needed to be pointed out that they were two different things, more or less falling along the lines of venom/injection, poison/ingestion.
How far back did this idea of the delivery method being a distinction go? 50 years? 100 years? 14th century?
I think it’s even more limited than that. Venomous is the term for an animal that injects a toxin with a pointy bit. Scorpions, snakes and lion fish are venomous. Tree frogs, expired yogurt and blow gun darts are poisonous even if they get into you different ways (absorption through the skin, ingestion and injection in this case)
When I worked in a venom lab in the 1970s, we used the words interchangably in conversation, but we did refer to our company as a venom lab, not a poison lab. I never ran into nitpickery on this topic until I started reading SDMB, and it makes me roll my eyes every time I see it.
They seem to have been used with almost equal frequency until about 1880, when poisonous snake began to be preferred. Interestingly, this is the opposite of the change one would expect if people were starting to apply the nitpicking definition. They begin to run in parallel after 1940.
When I took herpetology in 1972, I don’t ever recall a distinction being made. I’ve only heard this supposed distinction within the past decade or so.
I took herpetology in maybe 1989 or 1990 and I don’t really recall it being brought up then either - I’m pretty certain we used the terms interchangeably. But I do recall it being brought it up roughly around that time in relation to marine invertebrate biology ( i.e. “Conus snails are venomous, not poisonous” ). Apparently the invertebrate folks won the semantic war ;).
I think many of us in the USA treated Roger Conant’s Field Guide to Reptiles and Amphibians as sacred scripture when we were in our formative years. He labels the sections of the book that cover snakes “Harmless Snakes” and “Poisonous Snakes”. In the section about snakebite, he uses venomous and poisonous about equally.