The water of the sea comes and goes in tides. Twice each day the water rises—then it is high tide. After each high tide the water goes back—then it is ebb tide. Each tide lasts six hours.
When the snow melts in the spring, or when much rain falls, the water rises high in the brook. In the dry, hot days the water is low in the bed of the stream. If the stream or brook were full and low twice each day, the change would be like the high and low tides of the sea.
When the tide is low, Mr. Crab digs out his house. He scoops out the sand with his big claw. Then he folds his claw to carry the sand, as you can carry grass or leaves on your arm. Some kinds of crabs carry the sand in three of their feet, bent to form a basket.
Mr. Crab takes the sand to the top of his hole. Then, with a jerk, he throws the sand into a heap. The crab is very strong. He can lift and carry things larger than his body.
He digs out a long hall. He makes rooms in his house. Then he goes with his wife to look for food. They keep near their home.
They eat flies, gnats, ants, lady-birds, and other little insects. They also eat sea-weed. When beach-flies light on the sand or on sea-weed, the crabs jump at them, and catch them as cats catch mice. But the cats do not move so quickly as the crabs. Mr. and Mrs. Crab put the bugs they catch into their pantry.
For six hours, while the tide is high, they stay in their house; and while they stay in the house they eat insects and sea-weed they have stored away.
The crab acts as though he knew about the tide. He knows when it will be high over his house. He knows when it will be low, so that he can come out.