I caught this pair of Sally Lightfoot Crabs clashing head to head. Perhaps they were tussling over food, or simply because of their aggressive nature. The crab on the top is pushing the bottom crab backwards, and within thirty seconds after I made this picture both of them tumbled out of sight into a deep crevice on this lava field battleground. I saw hundreds of these crabs during my two week visit to the Galapagos, and this was the only time I observed such aggressive behavior.