Behavior

As expected, behaviors are extremely diverse among Col-ubridae and generally poorly known, with the exception of a few common or unusual species. The behavior of a species often reflects its environment, and arboreal, cryptozoic, and fossorial species are especially difficult to study behaviorally. Defensive behavior, in particular, seems to reflect both coloration and habitat. Many species are cryptically colored (camouflaged) and, in the various vinesnakes, similarity to the snake's surroundings is enhanced by the narrow body and pointed head. More active defenses include threat displays, which may involve flattening the body, as in many North American watersnakes (Nerodia); spreading of a horizontal hood reminiscent of cobras, as seen in the xenodontine false water-cobras (Hydrodynastes); or vertical inflation of the neck, as in the colubrine tiger ratsnake (Spilotes). In general, horizontal displays characterize terrestrial species, whereas arboreal ones have vertical displays. Tail displays also occur in some species, such as the xendontine ring-necked snakes (Di-adophis), in which the tail is upturned to show the bright ventral coloration and is moved in a distinctive spiral action. Other species gape when confronted by a predator and many bite, although others simply attempt to escape. Asian natricine snakes of the genera Rhabdophis and Balanophis have glands on the dorsal surface of their neck or along their entire back that exude a noxious compound when the snakes are threatened. Tail loss is rare among snakes, but a few taxa apparently lose the tail freely to escape predators, including the neck-banded snake (Scaphiodontophis), a Neotropical colubrine. Unlike the tails of some lizards, those of snakes do not regenerate if lost. Mimicry is common among snakes. Some species, such as the false pitvipers (Xenodon), mimic vipers, while in the Neotrop-ics many species of xenodontines and a few colubrines mimic the elapid American coral snakes (Micrurus).

Colubrid snakes do not appear to be territorial. Instead, the males of some species, especially among the colubrines, are known to engage in ritual combat to obtain access to mates. Such combat generally resembles that of vipers and elapids, with the individuals intertwining their bodies and attempting to topple each other. That behavior may have served as the inspiration for the caduceus, the staff with entwining snakes that was said to have been carried by the god Hermes and that now is emblematic of the medical profession. In some species biting may also occur during combat. Species with male combat generally exhibit sexual size dimorphism in which males are larger than females, reflecting the fact that larger males generally are more successful in combat and therefore are favored to reproduce. Some other species exhibit the opposite pattern of sexual size dimorphism, in which females are larger than males. That condition reflects selection in which larger female size is associated with greater numbers of offspring.

Courtship behavior is known in a number of colubrid species, and it generally involves the male tongue-flicking and pressing his head along the back of the female. If the female is receptive, the male inserts one of his paired hemipenes into the female's cloaca to inseminate her. Males often locate females by following pheromone trails, a behavior mediated by the vomeronasal organ located in the roof of the mouth. That w «REr

The common egg-eater snake (Dasypeltis scabra) must unhinge its jaw to eat an egg. (Illustration by Barbara Duperron)

organ receives cues from the environment by means of the tongue tips. In some species courting males aggregate around females and compete for matings, as in certain Canadian populations of the common gartersnake (Thamnophis sirtalis).

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