Toxin, as far as I can tell, specifically means a pure substance that is toxic, like botulinum toxin (the molecule). A venom can have multiple toxins.
Anyway, to labour the point about usage, it’s always been normal to refer to animals that can poison you by biting you as “poisonous”. Here’s an example in a published book from every century from the 17th to the 21st:
1668, John Wilkins, chapter V, in An Essay Towards a Real Character, and a Philosophical Language, London: […] Sa[muel] Gellibrand, and for John Martyn printer to the Royal Society, →OCLC, 2nd part (Conteining a Regular Enumeration and Description of All Those Things and Notions to which Names are to be Assigned), page 161:
SERPENT … either that which is not poiſonous: or that which is counted poiſonous, having two long, hollow, moveable teeth, …
1787, F.S. Clavigero, The History of Mexico[2], London: G. G. J. and J. Robinson, page 60:
The Cencoatl (o), which is alſo a poiſonous ſnake, is about five feet long, and eight inches round at the thickeſt part.
1895, Leonhard Stejneger, The Poisonous Snakes of North America[3], Washington: U.S. Government Printing Office, page 475:
Evidently the first thing to ascertain is whether the case is really that of a bite by a poisonous snake…
1963, United States. Navy Department. Naval Operations Office, Poisonous Snakes of the World[4], U.S. Government Printing Office, page 29:
The characteristics which separate the dangerously venomous groups from their non-poisonous relatives are emphasized.
2002, B. Kalman and K. Smithyman, The Life Cycle of a Spider[5], Crabtree Publishing Company, page 31:
These antivenins make living near poisonous spiders much safer.
Toxin, as far as I can tell, specifically means a pure substance that is toxic, like botulinum toxin (the molecule). A venom can have multiple toxins.
Anyway, to labour the point about usage, it’s always been normal to refer to animals that can poison you by biting you as “poisonous”. Here’s an example in a published book from every century from the 17th to the 21st:
1668, John Wilkins, chapter V, in An Essay Towards a Real Character, and a Philosophical Language, London: […] Sa[muel] Gellibrand, and for John Martyn printer to the Royal Society, →OCLC, 2nd part (Conteining a Regular Enumeration and Description of All Those Things and Notions to which Names are to be Assigned), page 161:
1787, F.S. Clavigero, The History of Mexico[2], London: G. G. J. and J. Robinson, page 60:
1895, Leonhard Stejneger, The Poisonous Snakes of North America[3], Washington: U.S. Government Printing Office, page 475:
1963, United States. Navy Department. Naval Operations Office, Poisonous Snakes of the World[4], U.S. Government Printing Office, page 29:
2002, B. Kalman and K. Smithyman, The Life Cycle of a Spider[5], Crabtree Publishing Company, page 31: