The City Sewers is a smelly, dirty, disgusting place to visit. Not many pets can live here, but its home to a lot of insects and bugs. The Crevice is a giant gap in the walls of the sewers, where hundreds of different bugs live. The gap is too small for you or your pet to get into, but with a Trap you should be able to catch a bug. The better the trap, the rarer the bug!
Use any Trap from your Inventory to catch a bug. Once you catch a bug, you will lose the trap.