Squirrels - numbering around 270–280 species - are agile, tree-dwelling mammals found nearly worldwide. Known for scatter-hoarding food across vast territories, they possess an excellent spatial memory and use landmarks to retrieve hidden caches. Their front teeth grow continuously (up to 6 inches per year), requiring constant gnawing. To aid tree movement, squirrels can rotate their hind ankles 180°, allowing them to descend headfirst, an adaptation cats lack. Some species migrate to better territories, even swimming rivers in long, coordinated lines. Socially, squirrels have been observed adopting orphaned young, revealing a surprising layer of adaptability and care within their communities.