Viperids feed chiefly on small vertebrates, particularly rats, mice, and lizards, and less often on frogs and birds, paralyzing or killing their prey by biting it. Some of the smallest vipers prefer locusts, and various other vertebrate and invertebrate prey types are known. Many viperids are ambushers and generally lie in wait for their prey, sitting quietly in one spot for long periods of time. Other species may forage actively or employ a combination of active and ambush foraging. The most specialized ambushers may feed quite infrequently. Many species show an ontogenetic shift in prey preference, feeding on small ectotherms (e.g., lizards and frogs) as juveniles and taking endotherms (e.g., rodents) when they are adults. Caudal luring has been observed in juveniles of several viperid species (e.g., Bitis peringueyi and Agkistrodon contortrix), and this behavior is retained in adults of Bothriop-sis bilineata. Associated with caudal luring is a distinctive coloration of the tail tip—from black to brown to bright yellow or bright green, depending on the species. Many species with draw the head immediately after striking prey and subsequently locate the prey by using their Jacobson's organ. Other species, including many arboreal species, hold the prey until it is immobilized and then swallow it. Many vipers are useful for controlling rodent pests.
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