Duvernoy's Glands and "Warm" Herping
©2001 Michael Smith, Cross Timbers Herpetologist, September 2001, DFWHS
Every reptile keeper has his or her favorite herp. Some keep tortoises, others bearded dragons, and many have their favorite group of milk snakes or kingsnakes. A few herpers are drawn to venomous reptiles, and some of those wear it like a badge. Some of these folks consider that the pinnacle of herping is hot-keeping, and to this small group, working with hots places them a cut above the average hobbyist. A small sect, and not representative of all those with an interest in venomous reptiles, but nevertheless they have an influence on the hobby.
So, in my early days of herping, imagine my shame as I acknowledged my garter snake habit only to my most trusted friends. My self-esteem plummeted as I realized how much I was drawn to these lowly reptiles, dismissed by herper and non-herper alike with oh, its just a garter snake. I walked through reptile expos feigning interest in gray-banded kingsnakes and making vendors think I might shell out the money for a green tree python. If a vendor had a kindly face or seemed non-judgmental, I might lean over and whisper, You got any checkereds?
To my further shame, in the field with friends we would see speckled kingsnakes or western massasaugas, but my secret wish was to see a Texas garter snake. A friend might roll a log and find a Louisiana milk snake, and I could appreciate the pretty colors. We might drive the roads and find an exceptionally pretty copperhead, but my thoughts were elsewhere. I longed to flip a board and see the orange dorsal stripe of a Texas garter, and while I had come out about my attraction to garter snakes, I often wished Id been born a normal guy whose first love was rattlesnakes.
And then one day a miracle occurred: I learned that garters had Duvernoys gland secretions that were toxic, so that a person bitten could suffer swelling, bleeding, and bruising. My shame melted as I stood straight and tall and said to myself, Im a hot herper! Well, at least a warm herper! Lo and behold, the object of my long-term affections was at least a little bit venomous.
Many snakes have a long strip of tissue, the superior labial gland, running from snout to behind the angle of the upper jaw. This gland is beneath the labial (lip) scales on either side of the head, and secretions are discharged into the furrow between the lip and gum. In many colubrid snakes, the back part of the superior labial gland is differentiated into a separate gland, called the Duvernoys gland. While the labial gland produces mucus secretions, the Duvernoys gland produces proteins, the substances that make up venom. Duvernoys glands come in three types, with Type I being the least harmful. Type III glands are found in lethal rear-fanged snakes such as boomslangs.
Generally, it appears that many snakes developed one or another strategy for immobilizing prey, either constriction or envenomation. Being a legless animal without claws to hold prey and without the kind of teeth and jaws that can rip and tear, it was to the snakes advantage to develop some way to subdue a prey animal. Those that constrict generally did not develop any venom apparatus. Those that have some sort of venom generally do not constrict. Pough, et al. (1998) note that those colubrids that later evolved constriction, like the rat snakes and kingsnakes, have reduced Duvernoys glands.
There have been many reports concerning the venomous status of hognose snakes. (Hey, I have one of those, too!) The genus name, Heterodon, means different-toothed and refers to the enlarged teeth at the back of the upper jaw of the hognose. Steve Grenard (1994) reviewed these reports, with symptoms ranging from mild swelling, pain, and tenderness to profuse bleeding, swelling so that the hand could not be closed, numbness of the bitten hand (possibly from the swelling), nausea, dizziness, pain and bruising. The victims of these bites did not go to the hospital and no lab studies were done regarding their injuries, and so we cant conclusively say that they were envenomated, but it certainly seems that way. None of those bitten had any long-lasting problems from it.
Its important to add that, regardless of all this, hognose snakes are among our most inoffensive snakes. Many readers will know that hognose snakes are famous for not biting in self-defense, but go through an elaborate bluff to scare intruders off. Wild hognoses flatten and hiss and jerk their heads around in a way that suggests striking, but if a hand is offered they do not bite it. If hissing does not work, eventually they go into a spasm of contortions, ultimately flipping themselves onto their backs, as if dead. Turned back over, the snake will roll back over into the correct dead position with mouth hanging open.
Those rare bites that occur from hognoses tend to involve feeding. While the common name refers to the upturned hog-like snout, these snakes arent affectionately called hogs just for their noses! Well-established hognose snakes love to eat, and mine used to consider swallowing the tip of my finger; a pinkie is a pinkie, after all. A keeper who has been handling the snakes food could end up being chewed on and envenomated. Grenard even suggests that this might be the only way it would happen, as a frightened snake might get dry mouth from the action of epinephrine the ducts of the salivary glands would be constricted. So, even if a hognose were to bite defensively, the bite might be free of venom.
As to biting, garter and water snakes are a different story! How many of us have been chewed up one side and down the other by a water snake that weve picked up to examine or photograph? These little buzzsaws generally have no hesitation to bite. A number of the garter snakes will bite when initially caught, as well. Grenard cites a case from 1985 in which a 13-year-old received a prolonged bite from an eastern garter snake. The child had swelling, bruising of the skin, and coolness (temperature, not social status!) and was hospitalized. Lab values were normal and the child recovered without problems. Evidently this same child was subsequently bitten by garter snakes without symptoms, showing that the original symptoms were not the result of an allergic reaction but apparently the result of mild venom. (The fact that this child continued to be bitten by garter snakes also demonstrates that he must have been a dedicated garter-lover!) Reports of the bite of a separate species, the wandering garter snake, also suggest toxicity. Symptoms from the bite of this species (Thamnophis elegans) have included swelling, pain, and localized bleeding but not systemic symptoms.
As with the hognose snakes, there is no cause to call Steve Irwin to come and remove your pet garter snake. Of the countless children who have started their interest in reptiles by picking up garter snakes and sometimes being bitten by them it seems that a very few have reported any problem from their bites. Stay calm; there is no need to organize a Sweetwater-style garter snake roundup, with cowboys strutting around in a pit with hundreds of garters, or bravely trying to milk the Duvernoy secretions into an ice-packed flask (We take it to the laboratories, where the scientists an doctors are!). Some might be tempted to watch one of those roundup daredevils get into a sleeping bag with hundreds of garter snakes, but really there is no need for a garter snake roundup.
So, garter and hognose snakes are examples of basically harmless but not quite non-venomous snakes. It appears that the simple distinction venomous or non-venomous is an oversimplification. Even adding the third category rear-fanged venomous doesnt quite get it. There seems to be a range from non-venomous, to snakes with toxic Duvernoys secretions of type I, II, or III (with or without enlarged rear teeth or grooved rear fangs), to snakes with specialized venom glands and front fangs.
Regardless of the harmlessness of garter snakes, my newfound status as a warm keeper has led me to take certain steps. Ive got shift boxes in those cages now, and the garters all get handled on hooks no more of that daredevil free-handling! Theres a Sawyer extractor on the wall, and 9-1-1 is taped on the phone so I wouldnt forget in case of emergency. I called the zoo to check on supplies of antivenin, but they laughed at me. Nevertheless, Im writing Wyeth Pharmaceutical to see if I can interest them in producing, for the first time, North American polyvalent natricine* antivenin!
References and further reading:
Bellairs, A. (1970). The life of reptiles: Volume I. Universe Books, NY.
Grenard, S. (1994). Medical Herpetology. Reptile & Amphibian Magazine, Pottsville, PA.
Pough, F.H., R.M. Andrews, J.E. Cadle, M.L. Crump, A.H. Savitzky, & K.D. Wells (1998). Herpetology. Prentice-Hall, Upper Saddle River, NJ.
(Disclaimer: While the information about Duvernoys gland secretions is true, there really isnt any need for garter snake or hognose snake keepers to worry as long as they do not purposefully allow the snake to chew on them. On the other hand, some snakes make it into the pet trade that may be a real problem, such as some of the keelbacks. Know your snakes!)
* natricine refers to the subfamily of snakes that includes garter and water snakes.
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