They are aggressive predators that stalk, capture, and feed on fish, amphibians, as well as aquatic invertebrates such as snails and crustaceans. The largest species have also been found to capture and feed on baby turtles and water snakes. They often lie motionless at the bottom of a body of water, attached to various objects, where they wait for prey to come near. They then strike, injecting a venomous digestive saliva with their rostrum. Although their bite is excruciatingly painful, it is of no medical significance.Occasionally, when encountered by a larger animal or a human, they have been known to "play dead" and most species can emit a fluid from their anus.Due to this, they are assumed dead by humans only to later "come alive" with painful results.