Colubrids feed on a wide variety of prey. Some species are prey generalists, feeding on virtually any animals within an appropriate size range. The racer (Coluber constrictor), for example, is known to feed on a wide variety of prey, including mammals, lizards, frogs, baby turtles, and insects. Some wideranging species, such as the ring-necked snake (Diadophis punc-tatus), consume different prey in different parts of their range, while in others with varied diets, such as the common garter snake (Thamnophis sirtalis), prey preference is influenced by early experience with a particular prey. Location of prey frequently involves the use of chemical cues, which are picked up by the tongue and delivered to the vomeronasal organ. However, many terrestrial and arboreal snakes are also strongly dependent upon vision to locate prey.
More often, however, colubrids are prey specialists, preferring either a general class of prey, such as fishes, frogs, or mammals, or a very specific diet, such as lizard eggs or skinks. Unlike lizards, few snakes feed regularly on insects. Among colubrids, only a few lineages take large numbers of insects or other terrestrial arthropods, of which the sonorines are the largest. Even within that group, some (such as Sonora) take a variety of arthropods, whereas others specialize on particular arthropods, such as centipedes (Tantitta). Stenorrhina preys primarily upon scorpions, tarantulas, and grasshoppers. Some snakes specialize on prey of a certain shape. Often these are fossorial snakes, whose narrow heads limit them to relatively elongate prey. For smaller species these may be worms, whereas large species may feed on snakes or elongate lizards. Within the aquatic genus Farancia, the rainbow snake (F. ery-trogramma) feeds mainly on eels, whereas the red-bellied mudsnake (F. abacura) feeds primarily on elongate aquatic amphibians, such as sirens (Siren). Eggs are a rich, if seasonal, source of food for many snakes. The arboreal cat-eyed snakes (Leptodeira), of the Neotropics, feed both on frogs and on frog eggs that are laid on vegetation overhanging water, such as those of the red-eyed treefrog (Agalychnis callidryas). The soft-shelled eggs of lizards and snakes are eaten by a variety of snakes, including the scarletsnake, Cemophora, a North American colubrine, the Asian kukrisnakes (Oligodon), and several Neotropical xenodontine genera, such as Umbri-vaga and Enulius. An extreme case of specialization involves the egg-eaters (Dasypeltis), African colubrines that feed only on bird eggs. They consume eggs that may be several times the diameter of their own heads, forcing their nearly toothless jaws around the egg. Once in the esophagus, the eggs are cracked on ventral projections of the vertebrae; the shell is regurgitated and the liquid contents are swallowed. A few snakes possess hinged teeth, which fold back when their hard-bodied prey are consumed. Among these are several lineages of skink-eating snakes, including the neck-banded snake (Scaphiodontophis), a Neotropical colubrine, and some that feed on hard-shelled crayfish, including the striped crayfish snake (Regina alleni), a natricine from southeastern North America.
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