Yeah they are big. I saw several of them when I lived on the capitol atoll, Majuro, of the Marshall Islands. I saw some that were relatively small (abut 12" across) and some that were much bigger. One time I came across one in the middle of the night and I wasn't sure who was more frightened. I quickly ran around it hoping it couldn't run faster than me.
I read that the coconut crabs break open coconuts by smashing them against rocks then pulling the meat out of the nut. They have to be stong to do that. Anybody ever try to pry a coconut open with your hands without cutting the outside shell? Lets just say it is near impossible.
I just wonder what they taste like.