I have needed to catch a crab in my tank for about 3 yrs now but just didn't want to rip apart my tank to do it. so I built a trap out of acrylic, it is glued with weld-on on all sides except the top, that is just rubber banded for easier removal of any thing caught. it has been 2 nights now and no crab but I was sitting here this morning and did catch something!!!!