Differences Between Buccal Gland Secretion and Associated Delivery Systems of “True” Venomous Snakes and “Colubrid” Snakes: Low- Versus High-Pressure Gland Function and Canaliculated Versus Solid Dentition

An unknown number of non-front-fanged colubroid snakes possess Duvernoy’s glands that produce variably toxic secretions released under low pressure (due to a lack of muscular compression of the glands). This is in marked contrast to the highly muscular and thus pressurized glands of front-fanged colubroids such as viperids, elapids, and atractaspidids. While pressurized venom glands release a bolus of stored venom under high pressure (that may exceed 30psi), non-front-fanged colubroids inoculate their secretions into wounds produced by maxillary teeth that may be enlarged, posterior or mid-maxillary, and may or may not be grooved; but unlike those of front-fanged colubroids, they are never canaliculated (e.g., never hollow, or with a lumen). Dispholidus typus (boomslang), and possibly other members of the tribe, Dispholidini, have limited striated muscle insertion into the gland and thus may be considered to have a partially pressurized venom delivery system. Several hypotheses have been considered that attempt to address the evolution of the venom apparatus and the selection for venom delivery systems. The definition and use of the terms “venom,” and “venom gland” require evidence of biological use of the oral secretion in prey subjugation and/or defense. The possible clinical effects of ophidian oral secretions do not constitute criteria for use of the term “venom.” As evidence of biological use of Duvernoy’s secretion becomes established, some of these complex mixtures may be termed “prey-specific venoms” in order to clarify their medical insignificance, while others, such as those of Dispholidus typus, the African twig, bird, or vine snakes, Thelotornis spp., the keel-backs, Rhabdophis spp., and, possibly, the Montpellier or hooded malpolon, Malpolon monspessulanus, have oral secretions that are used biologically and have concomitant medical importance. Others [such as the Puerto Rican racer, Alsophis (Borikenophis) portoricensis] may have secretions that are demonstrably used to subjugate a variety of prey, and also have occasional medical significance (e.g., a reasonable number of documented bites have caused significant local effects). Thus, the term “venom” may be used for the oral secretions of these taxa without any qualification.