Snail

Snails are picky about where they show up. They avoid Ice, Hallow and both evil biomes, stick to ordinary Underground and Cavern stone, and will not spawn in the lower half of the world at all. Nearby town NPCs suppress them the same way they suppress enemies, which is why they feel rare around a base.

Put up a patch of unsafe Living Wood Walls somewhere below the surface. Snails appear in front of them far more often than they do anywhere else, and those spawns ignore town NPCs entirely, so you can build the wall right beside your house and check it whenever you walk past.

As bait it is close to useless and only worth burning if you have nothing else in the box. The better uses are a Snail Cage for a room or cooking it into Escargot. Do not bother setting up a Snail Statue expecting free stock either, since statue-spawned critters cannot be netted at all and vanish in a puff of smoke the moment you try.