Colubrid snakes represent the largest and most diverse family of snakes, encompassing approximately two-thirds of all known snake species. This expansive group is found across nearly every continent, showcasing an incredible range of adaptations to various environments.
Understanding Colubrid Classification
The classification of colubrid snakes has historically been complex due to its role as a “wastebasket taxon.” This meant many species that did not fit neatly into other established families were grouped under Colubridae. This historical approach resulted in the family containing a wide array of snakes with diverse forms and behaviors, rather than a strictly natural evolutionary grouping.
Recent advances in molecular phylogenetics have begun to stabilize the classification within Colubridae. While the family is now considered a monophyletic clade, ongoing research continues to refine the relationships among the numerous genera and species. Eight subfamilies are recognized, with ongoing reclassification efforts occasionally moving certain groups into their own distinct families.
General Characteristics
Despite their immense diversity, some general physical and behavioral traits are common among colubrids. They lack any vestiges of hind limbs and do not possess external ear openings. Most species have broad scales on their bellies and often feature nine enlarged scales on the tops of their heads.
Colubrid snakes exhibit a wide range of sizes, from species as small as 6 inches (15.2 centimeters) to those reaching up to 12 feet (3.7 meters) in length. Their diets are varied, including insects, rodents, amphibians, and other reptiles. These snakes occupy diverse ecological niches, with many being terrestrial, others arboreal (tree-dwelling), fossorial (burrowing), or aquatic.
Venom and Defensive Strategies
Many colubrids are non-venomous, but some possess venom. Those that are venomous often have “rear-fanged” or opisthoglyphous dentition, meaning their venom-delivering fangs are located at the back of their upper jaw. Unlike front-fanged snakes, which can inject venom quickly, rear-fanged colubrids need to chew on their prey to deliver venom effectively.
The venom produced by most rear-fanged colubrids is mild and not medically significant to humans, often causing only localized swelling or bruising. However, a few species, such as the boomslang (Dispholidus typus) and twig snakes (Thelotornis species), are exceptions and possess venom potent enough to cause serious envenomations and even fatalities in humans. Beyond venom, colubrids employ various defensive behaviors, including bluffing displays, secreting foul-smelling musk, or mimicking more dangerous snakes. Hognose snakes may flatten their heads and hiss like cobras or even feign death when threatened.
Habitats and Global Distribution
Colubrid snakes inhabit nearly every continent except Antarctica and the extreme northern latitudes of Eurasia and North America. Their adaptability allows them to thrive in a vast array of environments. These habitats include arid deserts, dense forests, expansive grasslands, and mountainous regions.
Some colubrids are also well-adapted to aquatic life, residing in freshwater bodies and even some brackish (slightly salty) waters.
Notable Colubrid Species
A few well-known examples illustrate the diversity of colubrids. Garter snakes (genus Thamnophis), found across North and Central America, are generally slender with keeled scales and often display longitudinal stripes. Some garter snakes produce a mild neurotoxic venom, though it is not considered harmful to humans.
King snakes (genus Lampropeltis) are constrictors known for their striking patterns and ability to prey on other snakes, including venomous ones. Rat snakes (genus Pantherophis), found globally, are also constrictors and are often kept as pets due to their manageable size and docile nature. The boomslang (Dispholidus typus), an arboreal species native to sub-Saharan Africa, is recognized for its potent venom, which can be medically significant to humans. Hognose snakes (genus Heterodon) are characterized by their upturned snouts, used for digging, and their dramatic defensive displays, such as playing dead when threatened.