Largest structure built by a terrestrial animal

The largest structure built by a land animal is that of a beaver's lodge and dam. Beavers (genus Castor) of North America and Eurasia use mud, wood, vegetation and stones to dam up water to form a pond and then build a lodge for winter refuge. The longest beaver dam in the world measures some 850 m (2,788 ft) long. It is located in the far south of Wood Buffalo National Park in Alberta, Canada. This massive structure, which is more than twice the length of the Hoover Dam, was first spotted in 2007 by researcher Jean Thie (Canada) while studying satellite photos of the region. Its existence was confirmed by rangers from Parks Canada, who took pictures from a helicopter in May 2010. After reviewing old satellite and aerial photos, Thie concluded that the dam is the work of several generations of beavers, who have probably been working at the site since the mid-1970s.

Lodges typically measure 3-4 m (10-13 ft) across, 3 m (10 ft) high, and take 20 days to build using 3 tonnes (6,600 lb) of materials. On average, a family of four beavers can build 1.5 m (5 ft) of dam wall per day. The design of the dam usually reflects the rate of the water flow, i.e., the faster the water flows, the more curved the dam will be. Once the pond has been created, canals are excavated for the beavers to reach safely into the wooded areas (to collect more wood) by water and not on land where predators dwell. The longest documented canal measured 400 m (1,312 ft).

Beavers cut their own trees to strip it of branches and leaves. The largest documented tree to have been felled by a beaver was a cottonwood measuring 37 in (0.9 m) in diameter and 110 ft (33.5 m) tall.