https://youtu.be/NO1LXg1Puj8
Crabs walk for miles in the wild, they migrate in large groups at certain times of the year, and mine LOVE to get exercise. Obviously I can't let them walk for miles in western New York, but the wheel is the closest I can get to that.
To modify it, I took a (flat-backed) hamster wheel and drilled holes all around the perimeter. Then I attached pieces of craft mesh using tiny zip ties with the square part on the outside of the wheel. I made sure to extend the craft mesh an inch or so beyond the width of the wheel as my bigger crabs couldn't walk easily in the narrower confines of the unmodified wheel. (One was so determined before I modified it, she would hook a walking leg over the center post and hang on with that leg while the other legs walked the wheel.) The craft mesh (sold in single sheets--very cheap--in any craft store or even Wal-Mart) also gives them some traction which they seem to appreciate. Hope this helps.
