They grow to about 2 inches. I like these crabs a lot. but they tend to hide out in caves most of the day and arent too active, when they are active it tends to be at night. They prefer slightly brackish water (a little salt) and need a large space out of water. They like to spend 50% of the time in and 50% of time out of water so need an island, I wouldn't recommend putting them in a planted tank because they could easily destroy it so should generally go in a rock scaped tank. As Paulo says the tank needs to be covered. They are relatively easy to keep though.