However, crabs can survive for long periods out of water, and some live almost exclusively on land. As long as a crab can keep its gills moist, oxygen from the air will diffuse into the moisture, and then into the gills. One way to keep their gills from drying out is to seek out cool, dark and moist hiding places when on land. This way they can keep breathing and stay hidden from predators. Also, they have articulating plates around their gills that help seal them in and prevent drying out.
Land crabs have even more adaptations to prevent drying out.
They drink water from dew and the ground, they get it from food, and even from water vapor. They also store water in their bladder, blood, and specialized pockets throughout their bodies. Crabs cannot see very well and usually only use their vision when their prey is very close. This is kind of like our sense of smell. Click here for more information.