>>I think people tend to seriously underestimate the potential dangers of a lot of rear-fanged colubrids, particularly Hydrodynastes, Boiga, Psammophis and Leioheterodon. Some of these are known to possess a venom that has the potential to be dangerous to humans, particularly those that may be hyper-sensitive to some of the protiens and other compounds in them.
I have heard of cases of anaphylaxis after garter snake bites. Anaphylaxis is a whole different ball game, and has very little to do with the strength of the venom. After all, a bee sting is trivial to a non-sensitive individual.
>> Others are simply not understood well enough yet. It may also be that there are variations in toxicity from locale to locale, and the possibility of some of them being in the process of evolving more toxic venoms. The only way that you know if you are hypersensitive is to get bitten. As a rule, there is no Antivenin for these venoms. It may well be that there are no recorded human fatalities for a particular species, but there was always a first one for every species that is known to kill people. As Wolfgang pointed out, at one time Thelatornis and Dispholidus were considered "harmless" and had even reportedly appeared in pet stores for sale. Any rear fanged colubrid MUST be handled and treated as a potentially dangerous animal.
It's basically a matter of considering how much or how little we know about the snake in question, both from the point of view of the toxins and itneractions with humans. For some colubrids, there has been a long history of intensive interaction without major problems - for instance, Thamnophis have been kept in their hundreds of thousands by kids, and once in a while, someone got a sore hand. However, after so many interactions, we can be reasonably confident that we have seen the full envelope of what Thamnophis can do to us. I would be truly amazed to hear of a life-threatening Thamnophis bite. One could argue the same for Heterodon nasicus - very nasty swollen arms, yup, but fatal? - very unlikely.
However, for many other colubrids, we don't have a sufficiently extensive history of human interaction to be sure of the worst-case potential. Psammophis aren't kept all that commonly by herpetoculturists, so the fact that there have been some bites with minimal envenomation cannot be taken as an indication that more serious bites are impossible. South African field guides generaly recommend caution when dealing with larger species, and we know that they have a large venom yield and some pretty hot toxins, including neurotoxins. That should certainly ring some alarm bells.
The same applies to other rare species, or those that have only recently become available. After all, Rhabdophis subminatus was a popular pet snake in the 70's and 80's, until a series of life-threatening bites woke everyone up. I suspect that there are a number of "next Rhabdophis" out there in the wonderful world of colubrids, and someone, somewhere, will one day have a very unpleasant surprise. Point is, don't be first to find out.
Cheers,
Wolfgang
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