I've been watching the tiny black-clawed crabs in my tank. The female is still only about a centimetre (1/2 inch) across, and weighs about 2 grams, according to my food scale*. She has chosen the base of a large stone as her preferred hiding place, kicking out the larger male who lived there earlier. Yesterday, the stone was tipped almost onto its side. This morning, it was straightened up again, but turned at a right angle from its previous position.
I took the stone out and weighed it. A little over 250 grams, more than half a pound, That's over 100 times the weight of the crab that's shifting it around.
|Two legs to hold the rock, four to lift it, and two pincers to wave at intruders.|
(*I weighed her in a plastic cup, with a bit of water for comfort, and then the cup and water alone. The crab made barely any difference.)