The tropics are lush because they are often awash in rain. Tropical ants must adapt to the sometimes-soggy conditions, even those that live in trees, as they may be dropped into the drink.
Not surprisingly, dozens of different tropical ant species independently evolved the ability to swim, though some do so better than others. Some ants swim with front and middle legs in a synchronized manner. Others are less coordinated. A few species can stand up and literally walk on water. Once dunked, all ants proceed in a determined and directed way.