Put this in deep water, load it up with 5 of any type of bait, and wait... Come back and check the trap by punching it occasionally. It may be days before an animal will wander in! You just better hope they don't wander back out with your bait.
The Lobster Trap is an unsplicable non-solid foreground block which was added as part of the Gone Crabby! update on March 3, 2016.
Function
To use a Lobster Trap, place five of any bait inside the trap. It can take anywhere between 1-2 days before the trap is ready, the more Water Buckets placed on and above the Lobster Trap, the higher the lb. (max of 3 Water Bucket placed above). However, there is a chance that the "The bait was eaten" text will appear in red when you punch it and no crab will be obtained. If a Lobster Trap remains unharvested for approximately 24 hours after it is ready, upon harvesting, the "You left the trap for too long, the baits are gone!" text will appear in red, with no crab being awarded. The location of where the trap is placed in the world does not matter, as long as it has its necessary depth. Punching it will give any of the following:
The given sizes above indicate what is the max possible size you can obtain from the trap. For example, a Lobster Trap with 0 depth and baited with 5 Wiggly Worm will only yield a size from 1lb. to 5lb.
Trivia
Lobster Trap only consider the placed Water Buckets on top of it. Even if there are some foreground blocks placed above it, the traps will ignore them and function normally.