Beavers build their houses, or "lodges," under the banks of rivers and lakes, and always select those of such depth of water that there is no danger of their being frozen to the bottom.
When such cannot be found, and they are compelled to build in small rivulets of insufficient depth, these clever little creatures dam up the waters until they are deep enough.

The banks thrown up by them across rivulets for this purpose are of great strength, and would do credit to human engineers.

Their lodges are built of sticks, mud, and stones, which form a compact mass; this freezes solid in winter, and defies the assaults of that housebreaker, the wolverine, an animal which is the beaver's implacable foe.

From this lodge, which is capable often of holding four old and six or eight young ones, a communication is maintained with the water below the ice, so that, should the wolverine succeed in breaking up the lodge, he finds the family "not at home," they having made good their retreat by the back-door.

When man acts the part of housebreaker, however, he cunningly shuts the back-door _first_, by driving stakes through the ice, and thus stopping the passage.