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.