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Untill recently, Colubridae has been a family which was used to dump into all advanced snakes that were not cobras, vipers or pitvipers. This made Colubridae the largest family of snakes, albeit with disputable taxonomic relationships. This group was heavily polyphyletic: a group that consist of species that are not all descended from one common ancestor, but from two or more. The contrary is monophyletic: a group that consist of species all descended from one common ancestor. The latter is, off course, is what we look for in order to resolve taxonomic relationships.
Some colubrids were later found to be more closely related to cobras (Elapidae), others to vipers and pitvipers (Viperidae). Nicolas Vidal and collegaues have examined this taxonomic dump and came up with a new tree of relationships that more closely resembles the truth. This meant that Colubridae as dump family, was no more. Many species in Colubridae deserved their own family. And they were give so by Vidal and collegaues.
But over the years, the term 'colubrids' was so heavily graved into snake biology that it is now still used to talk about all those advanced snakes that are not cobras, vipers or pitvipers. But this must not be confused with the family Colubridae.
Colubrids are often slender, agile snakes that can be found all over the world. They come in all sizes and colors, and many of them have fascinating behavioural adaptations. For example, the snakes of the genus Chrysopelea, or flying snakes, launch themselves from one treetop to the other in Asian rainforests, gliding through the air through flattening their bodies to serve as parachutes.
Many colubrids feed on small, non-dangerous prey like lizards and frogs. They kill their prey through constriction, often helped by injecting some venom. Many colubrids are technically venomous, although harmless for man. Their fangs are located in the back of the upper jaw, in contrast with cobras, vipers and pitvipers, which are front-fanged. Colubrids need to chew venom into their prey, and thus they cannot inject much venom in short time. Their venom-system is much less advanced as that of the front-fanged snakes, not only in terms of fangs, but also in terms of venom glands. Colubrids lack the compressor muscles that cause rapid venom expulsion in front-fanged snakes, and they lack a lumen (storage room) for the venom. There are exceptions, however. African boomslangs (Dispholidus) and the African cape file snakes (Mehelya), both colubrids, have some muscle attachment to their venom glands. The boomslang is, in addition, also the most dangerous colubrid snake that we know of to date. People have died from bites by this species. The most famous case is that of renowned snake expert Karl P. Schmidt, who got bit by a boomslang in 1957 and died.
With a few exceptions, most colubrid snakes are completely harmless to man. I have been bitten by numerous colubrid snakes, and never suffered from any envenomation symptom. That said, I am very carefull around the exceptions and the colubrid snakes that we know little about. I don't want to be the first to find out that a certain species is capable of causing severe envenomation symptoms!