This open mouth threat display has led to the widespread belief that cottonmouths are aggressive snakes. Some people believe cottonmouths lie in wait on tree limbs overhanging water so they can drop into boats. These are usually cases of mistaken identity. The harmless brown watersnake often basks on tree limbs over the water, and when frightened by a rapidly approaching boat, they will escape by throwing themselves off the limb and into the water. Occasionally the watersnake's attempt to flee comes too late and it falls not into the water, but into the boat.
Cottonmouths feed on fish, frogs, mice, rats, and other small mammals.
Juvenile cottonmouths have a bright, sulfur-colored tail which they hold erect and wiggle like a caterpillar to attract prey within striking range. Though the cottonmouth occurs throughout Florida, it is not as abundant as the many species of harmless watersnakes that occur in the same habitats. Many Florida residents do not even realize that watersnakes exist. As a consequence, every large dark-colored snake found near water is counted, and usually killed, as a cottonmouth. There is little justification for this error for cottonmouths can easily be distinguished from watersnakes .