Welcome to Friday Fiction Facts: sciency things that fiction writers need to know.

Some spiders are venomous, but not this wolf spider. Photo: Chris Buddle)

All spiders produce venom, but most, like this wolf spider, are not venomous to humans.* (Photo: Chris Buddle)

Alright fiction writers, what’s wrong with these sentences?

“… indeed, who could distinguish the two little dark punctures which would show where the [snake’s] poison fangs had done their work. ”  – Sir Arthur Conan Doyle, “The Adventure Of The Speckled Band

“And it is observed, that the Pike will eat venomous things (as some kind of Frogs are) and yet live without being harmed by them” — Izaak Walton “The Compleat Angler”

I’m sure my title gave it away. Snakes are venomous. Frogs are poisonous. Confusing these two things is a common mistake, but the difference between them is pretty straightforward. Put simply  —

Venomous — a creature or thing is venomous if it injects poison by way of fangs, barbs or a stinger.

Poisonous — a creature or thing is poisonous if it poisons you when you touch it, eat it or inhale its fumes.

While the difference may seem pedantic or prescriptive to English scholars and linguists, who trace the more general use of poisonous as a synonym of venomous back to the 1600’s, this is not a grammar distinction, but a scientific one. To argue it based on historical usage is a bit like saying that, because Melville referred to a whale as a fish, then the sentence “A whale is a fish” is acceptable. Yes it is grammatically correct. No, it is not scientifically correct.

Here is a wonderful explainer by Rose Eveleth, animated by Celeste Lai —

* edited caption 7/12/14

** Update 7/22/14: Here is a delightfully illustrated explanation.