Hi bros,
Sharing a personal experience I had recently.
After so many months of having my tank, I saw a crab in it for the first time 2 weeks back after the lights were out. I decided to leave it for the night and immediately regretted after doing a Google research the next day and finding out that crabs can be harmful. So, I was determined to get that crab out.
Googled some ideas and decided to use a glass bottle at home as a crab trap. The idea was to lean the bottle against the rock and put a bait (prawn meat) inside. When the crab climbs in to eat at night, it will not be able to climb out because there is no grip on the glass for it. Left the trap there for 2 nights but the crab was not caught. Fortunately, spotted the crab again one of the nights and manage to spear it with a chopstick!
Nevertheless, really liked the DIY crab trap and was just glad to have gotten the crab out whether by the trap or the spearing