at least 1850, when
the magnificently named bibliophile the Comte de Bastard theorised that a particular marginal image of a snail was intended to represent the Resurrection, since he discovered it in two manuscripts close to miniatures of the Raising of LazarusAlas, he failed to convince anyone else. (Two from the Gorleston Psalter, made in Suffolk, England c. 1310-1320.
Hunting for Snails, a blog devoted to snails in art. Really.
That's enough amusement for now. Go do something serious and important.